Signetics: Microcontroller Users' Guide

INTEGRATED CIRCUITS
Signetics
Microcontroller
Users'
Guide
PHILIPS
SCN8031 AH/SCN8051 AH SC80C31B/SC80C51B SC87C51 S83C751
~ INDEX
"""tj
Pl.D 1 40 Vee 40 Vee P3A 1 24 Vee
39 PO.O/ADO 23 P3.5
P1.1~ 39 PO. alA DO 7 0 39 P3.3~
P3.2~ 22 P3.6
:::!~
38 PO.t/ADt
Lec 21 P3.7
:~:~+
~ PO.2/AD2
20 P1.7/TO
PtA 5 ~ PO.3/AD3
17 29 PO.2 6 DIP ~ P1.6/INTl
P1.5 6 35 POA/AD4
Pl.B 7 34 PO.5/AD5 18 28 PO.l/SDA 7 18 P1.S/INTO
Pt.? 8 33 PO.S/AD6 TOP VIEW PO.O/SCL 8 17 P1A
15 P1.3
RST~ 32 PO.l/AD? Pin Function Pin Function RST , ;
DIP 15 P1.2
~~ ~
RxD/P3.0~ DIP 31 EA 1 NC 23 NC
2 PloD 24 P2.0/A8 14 Pl.1
,~~~;:~:: ~
30 ALE 3 P1.1 P2.lIA9
25
29 PSEN 4 Pl.2 26 P2.2/Al0 Vss 12 13 P1.0
M1/P3.313 ~ P2.7/A15
5
6
P1.3
Pl.4
27
28
P2.3/Al1
P2.4/A12
28 P2.7IA1S -
TOP VIEW
TO/P3.4 14
Tl/P3.515
27 P2.S/A14
26 P2.5JA13
,
7 Pl.5
P1.6
29
30
P2.5/A13
P2.6/A14 Tl/P3.5 15
27 P2.6/A14
26 P2.5/A13 INDEX
~/P3.6~ 25 P2.4/A12
9
10
Pl.?
RST
31
32
P2.7/A15
PSEN
WR/P3.6 16 25 P2.4/A12 CORNER 4 ~ 2. 25
11 RxD/P3.0 33 ALE RD/P3.7 17 24 P2.3/A11
R~~~:*
24 P2.3/Al1 G5
12 NC 34 NC XTAL2 18 23 P2.2/Al0
23 P2.2/Al0 13 TxD/P3.1 EA
35 PLCC
XTAl119 14 mT6/P3.2 PO.7/AD? XTAL1 19 22 P2.1/A9
22 P2.1/A9 36
Vss 20 15 iiii'i"i/P3.3 37 PO.6/ADe Vss 20 21 P2.0/A8
21 P2.0/A8 11 19
16 TOJP3.4 38 PO.5/AD5
"ToPViEW 17 T1/P3.S 39 POAIAD4 TOP VIEW
:r
18 WR/P3.6 40 PO.3/AD3 12 18
INDEX INDEX
19 1m!?3.? 41 PD.2/AD2 TOP VIEW
CORNER 6 1 40 XTAL2
20 42 PO.l/AD'
r~J 00"") ,:
21 XTALl 43 PO.C/ADO PI" Function Pin Function
Vee
'cr
22 V" 44 1 P3.4 15 Pl.0
2 P3.3 1. Pl.l
6 1 40
PLee 3 P3.2 17 Pl.2
4 P3.1 18 Pl.3
17 29 17 29 5 N.C. 19 P1.4_
,•
P3.0 20 Pl.S/INTO
18 28 QF? 18 28 7 PO.2 21 N.C.
PO.1/SDA 22 N.C.
TOP VIEW TOP VIEW 9 PO.O/SCL 23 Pl.6/INTl
PI" Function PI" Function 17 0 29 Pin FUnction Pin Function 10 N.C.
RST
24
25
P1.7/TO
P3.7
1
2
NC
P1.0
23
24
NC
P2.0/A8 18 28
1
2
3
NC
Pl.0
Pl.l
23
24
NC
P2.0/A8 "
12
13
X2
Xl
26
27
P3.6
P3.5
3 Plot 25 P2.t/A9 TOP VIEW 25 P2.1/A9
4 P1.2 P2.2/Al0 4 P1.2 26 P2.2/A10 14 V" 28 Vee
26 Pin Function Pin Function
5 Pl.3 27 P2.3/Al1 5 Pl.3 27 P2.3/Al1
6 Pl.4 P2A/A12 1 NC 23 V" 6 P1A 28 P2A/Al2
28
7 P1.S 29 P2.5/A13 2
3
PloD
Pl.1
24
25
P2.D/A8
P2.1/A9
7 Pl.5 29 P2.5/A13 S87C752
8 P1.6 30 P2.6/A14 8 Pl.6 30 P2.6/A14
4 P1.2 26 P2.2/Al0 9 Pl.? 31 P2.7IA15
9 Pt.? 31 P2.7/A15 P2.3/Al1
RST PSEN
5 Pl.3 27 10 RST 32 ~
10 32 P2.4/A12
6 Pl.4 28 11 RxD/P3.0 33 ALE/i'i1WG
11
12
13
RxD/P3.0
NC
IxD/P3.1
33
34
35
ALE
NC
EA
,
7
9
P1.5
Pl.6
Pl.?
29
30
P2.5/A13
P2.6/A14
P2.7/A15
12
13
NC
TxD/P3.1
34
35
NC
~lVpp
31 14 iNIo/P3.2 36 PO.7/AD7
14 mro/P3.2 36 PO.l/AD?
10 RST 32 ~ 15 mfi/P3.3 37 PO.6/AD6
15 INTt IP3.3 37 PO.B/ADS 11 RxD/P3.0 ALE
33 1S TO/P3A 38 PO.5/ADS
16 TO/P3.4 38 PO.S/ADS NC
12 NC 34 17 T1/P3.S 39 POAfAD4
17 Tl/P3.5 39 POA/AD4 13 TxD/P3.1 ~
35 18 WF'l/P3.6 40 PO.3/AD3
18 WR/P3.6 40 PO.3/AD3 14 ilimi/P3.2 PO.7/AD?
36 19 1'IT5/P3.7 41 PO.2/AD2
19 AD/P3.? 41 PO.2IAD2 15 INn/P3.3 37 PO.s/ADe
20 XTAL2 42 PO.t/ADt 20 XTAL2 42 PO.lIADl
16 TO/P3.4 38 PO.5/AD5 21 XTAL1
21 XTAL1 43 PO.D/ADO 43 PO.O/ADO
17 T1/P3.S 39 PO.4/AD4 22 Vss 44 Vee
22 V" 44 Vee 18 WR/P3.6 40 PO.3/AD3
19 M/P3.? 41 PO.2/AD2
20 XTAL2 42 PO.l/ADl S87C751
21 XTALl 43 PO.a/ADO
22 V" 44 Vee
P3AIA4 1
SC80C31B/SC80C51B P3.3/A3 2
P3.2/;~b 3
P1.0 1 40 Vee
P3.1/A~~ 4
Pl,' 2 ~ PO.a/ADO
Pl.2 3 38 PO.l/ADl P3.0/A~£ S
Pl.3 4 37 PO.2/AD2
PO.21Vpp 6 TOP VIEW
P1.4 5 36 PO.3/AD3
PO.l/SDAI
OE-PGM 7 INDEX
P1.5 6 35 POA/AD4
P1.6 7 ~ PO.5/AD5 Po.O/!~~L 8 eORNER
1 G26
4 25
Pl.7 8 33 PO.6/ADS
RST 9 32 PO.71AD7
PLCC
RxD/P3.0 10 DIP 31 EA
TxD/P3.1 11
~~~~N
11 19
INTO/P3.2 12
12 18
iNTI/P3.3 13 28 P2.7/A1S
TOP VIEW
TO/P3.4 14 27 P2.6/A14 TOP VIEW
Tl/P3.S 1S 26 P2.S/A13 INDEX Pin Function Pin Function
1 P3.4/A4 15 Pl.2/ADC2/D2
WR/P3.6 16 2S P2A/A12 CORNE,R 4 : 2. 25 2 P3.3/A3 16 Pl.3/ ADC3/o3
M/P3.7 17 24 P2.3/Al1 3 P3.2/A2fAl0 17 Pl.4/ADC4/D4
G5 4 P3.1/Al/AS 18 AVss
XTAL2 18 23 P2.2/Al0 19 AVee_
PLCC 5 P3.0/AO/A8
20 Pl.5/INTO/D5
XT:~: t¥o
22 P2.1/A9 6 PO.21Vpp
7 PO.1/SDA/ 21 Pl.6/INT1/D6
21 P2.0/A8 11 19 22 Pl.7/TO/D7
OE-PGM
TOP VIEW 8 po.o/seLl 23 PO.3
12 18 ASEL 24 PO.4/PWM
9 RST OUT
TOP VIEW
10 X2 25 P3.7/A7
Pin Function Pin Function 11 Xl 26 P3.6/A6
1 P3.4/A4 15 Pl.D/oO 12 Vss 27 P3.5/AS
2 P3.3/A3 16 P1.1/Dl 13 P1.0/ADCO/DO 28 Vee
3 P3.2/A2/A10 17 Pl.2/D2 14 P1.1/ADC1!D1
See inside of back cover for additional pins. 4 P3.1/Al/A9 18 Pl.3/D3
NOTE:
5 N.C. 19 Pl.4/D4
6 P3.0/AO/A8 20 Pl.siiNf'O/DS AO-A10 and 00-07 available for EPROM
7 PO.21Vpp 21 N.C. verify only.
8 PO.l/SDAI 22 N.C.
DE-PGM 23 P1.6/INT1/D6
PO.O/SCLI 24 Pl.7/TO/D7
ASEL 25 P3.7/A7
10 N.C. 26 P3.6/A6
11 RST 27 P3.S/AS
12 X2 28 Vee
13 Xl
14 Vss
Signefics Microcontroller
Users' Guide
Microprocessor Products
Signetics reserves the right to make changes, without notice, in the products, including
circuits, standard cells, and/orsoftware, described or contained herein in order to improve
design andlor performance. Signetics assumes no responsibility or liability for the use of
any of these products, conveys no license or title under any patent, copyright, or mask
work right to these products, and makes no representations or warranties that these prod-
ucts are free from patent, copyright, or mask work right infringement, unless otherwise
specified. Applications that are described herein for any of these products are for illustra-
tive purposes only. Signetics makes no representation or warranty that such applications
will be suitable for the specified use without further testing or modification. Portions of this
users' guide are printed under a license from Intel Corporation.
LIFE SUPPORT APPLICATIONS
Signetics Products are not designed for use in life support appliances, devices, or systems
where malfunction of a Signetics Productcan reasonably be expected to result in a person-
al injury. Signetics customers using or selling Signetics' Products for use in such applica-
tions do so at their own risk and agree to fully indemnify Signetics for any damages result-
ing from such improper use or sale.
Signetics registers eligible circuits under

the Semiconductor Chip Protection Act.
© Copyright 1989 Signetics Company

a division of North American Philips Corporation
All rights reserved.

Signefics Contents
Section 1 - 8051 Family

Family Overview. .. . . .. . ........................................................................ 1-1
Arch itectu re . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1-4
Hardware Description ............................................................................ 1-20
Programmers' Guide and Instruction Set ............................................................. 1-4B
EPROM Products .............................................................................. 1-111
SCNB031 AH/SCNB051AH Data Sheet .............................................................. 1-115
SCBOC31 B/SCBOC51 B Data Sheet ................................................................ 1-123
SCB7C51 Data Sheet ........................................................................... 1-133
Section 2 - 8051 Family Derivatives

B032/B052 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-1
SCNB032AH/SCNB052AH Data Sheet ................................................ . . . . . . . . . .. 2-11
BXC451 Overview ............................................................................... 2-1B
SCBOC451/SC83C451 Data Sheet .............................................................. 2-21
SCB7C451 Data Sheet ....................................................................... 2-35
BXC552 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-53
SB3C552/SBOC552 Data Sheet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-112
BXC652 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-123
SB3C652/SBOC652 Data Sheet ................................................................ 2-127
BXC751 Overview .............................................................................. 2-137
S83C751 Data Sheet ........................................................................ 2-144
SB7C751 Data Sheet ........................................................................ 2-151
8XC752 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-162
S87C752 Data Sheet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-16B
Section 3 - Application Notes

AN408 SCBOC451 Operation of Port 6 ............................................................... 3-1
AN417 256K Centronics Printer Buffer - Using the SC87C451 Microcontroller . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 3-12
AN418 CounterlTimer 2 of the 83C552 ............................................................. 3-26
AN420 Using up to 5 External Interrupts on 8051 Family Microcontrollers .................................. 3-33
Section 4 -Inter-Integrated (FC) Circuit Bus

12C Bus Specification ............................................................................. 4-1
12C Peripheral Selection Guide. . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . .. . . . . . . . . . . . . . . ................ 4-13
Section 5 - Development Support Tools

Development Support Tools ........................................................................ 5-1
In-Circuit Emulator for 8051 or 8052 Microcontroller ..................................................... 5-2
In-Circuit Emulator for 80C451 Microcontroller ......................................................... 5-4
In-Circuit Emulator for 80C652 Microcontroller ........................................................ 5-10
In-Circuit Emulator for B3C751 Microcontroller ........................................................ 5-12
ASM51 8051 Macro Cross Assembler ............................................................... 5-14
SPGM-100 EPROM Microcontroller and Standard EPROM Programmer ................... , ................ 5-16
Section 6 - Additional Microcontroller Data Sheets

BX305 Microcontroller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 6-3
8X401 Microcontroller ............................................................................ 6-2B
SCNB049 Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 6-4B
Section 7 - Sales Offices, Representatives & Distributors ................................................. 7-3
April 1989 v
Signetics Section 1
8051 Family
INDEX
Family Overview .......................................... 1-1
8051 .................................................. 1-1
8051AH ................................................ 1-1
80C51 BH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1-1
8052AH ................................................ 1-1
83C451 ................................................ 1-1
~C~ ............................................... 1~
83C652 ................................................ 1-3
83C751 ................................................ 1-3
83C752 ................................................ 1-3
Architecture . . . . . . . . . . . . ...................... 1-4
Members of the Family .................................... 1-4
8051 ................................................ 1-4
8051AH .............................................. 1-4
80C51 BH ............................................ 1-4
8051 Family Devices Memory Organization .................... 1-4
Program Memory ........................................ 1-4
Data Memory ............................................ 1-6
8051 Family Instruction Set ................................. 1-8
Program Status Word ..................................... 1-8
Addressing Modes ....................................... 1-8
Direct Addressing ........................................ 1-8
Indirect Addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1-8
Register Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1-8
Register-Specific Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1-8
Immediate Constants ..................................... 1-9
Indexed Addressing ...................................... 1-9
Arithmetic Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1-9
Logical Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1-10
Data Transfers ......................................... 1-11
Internal RAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1-11
External RAM . ....................................... 1-12
LookupTables ........................................ 1-12
Boolean Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1-13
Relative Offset ....................................... 1-14
Jump Instructions ..................................... 1-14
CPU Timing ............................................ 1-15
Machine Cycles ......................................... 1-15
Interrupt Structure ....................................... 1-16
Interrupt Enables ..................................... 1-16
Interrupt Priorities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1-16
Simulating a 3rd Priority Level in Software .................. 1-18
Hardware Description
Special Function Registers ................................ 1-21
Accumulator ......................................... 1-21
B Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1-21
Program Status Word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1-21
Stack Pointer ........................................ 1-21
Data Pointer ......................................... 1-21
Ports 0 to 3 .......................................... 1-21
Serial Data Buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1-22
Timer Registers Basic to 8051 ........................... 1-22
Control Registers for the 8051 ........................... 1-22
Microcontroller Users' Guide
INDEX (Continued)
Port Structures and Operation ................................... 1-22

I/O Configurations .......................................... 1-22
Writing to a Port ............................................ 1-24
Port Loading and Interfacing .................................. 1-25
Read-Modify-Write Feature ................................... 1-25
Accessing External Memory ..................................... 1-25
Timer/Counters ............................................... 1-26
Timer 0 and Timer 1 ......................................... 1-26
Mode 0 ................................................... 1-27
Mode 1 ................................................... 1-27
Mode2 ................................................... 1-27
Mode 3 ................................................... 1-27
Standard Serial Interface ....................................... 1-27
Multiprocessor Communications ............................... 1-29
Serial Port Control Register ................................... 1-29
Baud Rates ................................................ 1-30
Using Timer 1 to Generate Baud Rates .......................... 1-30
More About Mode 0 ......................................... 1-30
More About Mode 1 ......................................... 1-31
More About Modes 2 and 3 ................................... 1-34
Interrupts .................................................... 1-34
Priority Level Structure ....................................... 1-37
How Interrupts are Handled ................................... 1-38
Externallnterrupts .......................................... 1-38
Response Time ............................................ 1-39
Single-Step Operation ......................................... 1-39
Reset ...................................................... 1-39
Power-On Reset ............................................. 1-40
Power-Saving Modes of Operation ............................... 1-40
CHMOS Power Reduction Mode ............................... 1-40
Idle Mode ................................................. 1-41
Power-Down Mode ......................................... 1-41
On-Chip Oscillators ........................................... 1-42
HMOS Versions ............................................ 1-42
CHMOS Versions ........................................... 1-43
Internal Timing ............................................... 1-43
Pin Descriptions .............................................. 1-43
8051 Programmers' Guide and Instruction Set ...................... 1-48
Memory Organization .......................................... 1-48
Program Memory ............................................. 1-48
Direct and Indirect Address Area ................................. 1-48
Interrupts .................................................... 1-52
Timer Set-Ups ............................................... 1-55
8051 Family Instruction Set ...................................... 1-59
EPROM Products ............................................. 1-111
Programming the 87C51 , 87C451, 87C552 ........................ 1-111
Programming Verification ... , .................................. 1-112
EPROM Erasure ..... " ...................................... 1-113
Programming the 87C751, 87C752 .............................. 1-113
SCN8031 AH/SCN8051 AH Data Sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-115
SC80C31 B/SC80C51 B Data Sheet .............................. 1-123
SC87C51 Data Sheet ........................................ 1-133
Section 1
8051 FAMILY OVERVIEW
The Signetics 8051 family of products is based on the 8OC5lBH

industry standard for 8-bit high performance micro-
controllers. The architecture for the family has been The 80C51BH is the CHMOS version of the 805l.
optimized for sequential real time control applications. Functionally it is fully compatible with the 8051, but
The 8051 family of products are used in a wide range of being CMOS it draws less current than its HMOS coun-
applications from those that are relatively simple to terpart.
applications in medical instrumentation and automobile
control systems. All of the devices included in the family The ROMIess version of the 80C51BH is the 80C31BH.
are available in versions that have either internal ROM, The EPROM version is the 87C5l.
EPROM, or CPU only. With the exception of the
83C751 and 752 (which are limited to on-board memory) 8052AH
all of the devices in the family c an address up to 64k
bytes of both program and data memory. The 8052AR is an enhanced version of the 805l. It is
fabricated with HMOS II technology, and is upwards
The 8051 family of microcontrollers includes the devices compatible with the 805l. Its enhancements over the
listed in Table 1. The basic architecture of these devices 8051 include:
is shown in Figure l.
• 256 bytes of on-chip data RAM
8051 • Three counter/timers
• A 6-source interrupt structure
The 8051 is the original member of the family. Among • 8K bytes of on-chip program memory
the features of the 8051 are: • 40-pin DIP and 44-pin PLCC packages
• 8-bit CPU optimized for control applications
• Extensive Boolean processing (single bit logic) capa- The ROMIess version of the 8052AH is the 8032AR.
bilities
• 32 bi-directional and individual addressable I/O lines 83C4S1
• 128 bytes of on-chip data RAM
• Two 16-bit timer/counters The 83C451 is an extended I/O version of the 80C51
• Full duplex UART with the following features:
• 5-source interrupt structure with 2 priority levels • Seven 8-bit quasi-bidirectional I/O ports (PLCC ver-
• On-chip clock oscillator sion).
• 4K bytes of on-chip program memory • Six 8-bit and one 4-bit quasi-bidirectional I/O
• 64K bytes program memory address space ports (DIP version).
• 64K bytes data memory address space • Mailbox port (port 6) features:
• 40-pin DIP and 44-pin PLCC packages tI Operation as normal quasi-bidirectional I/O port
tI 4 handshake control pins
The 8031 is a CPU only version of the 8051 and only tI Control status register
differs from the 8051 in that it does not have on-chip tI Input and output buffer registers making port 6
ROM. The 8031 fetches all instructions from external suitable for:
memory. • direct MPU interface
• parallel printer interface
805lAH • 64-pin DIP and 68-pin packages.
The 8051AH is identical to the 8051, but is fabricated All other aspects of the 83C451 are identical to the
with HMOS II technology. It is pin-for-pin compatible 80C5l. The 87C451 is the EPROM version of this de-
with the 805l. The ROMless version of the 8051AH is vice.
the 8031AH.
Table 1. 8051 Family of Microcontrollers

Device ROM less EPROM ROM RAM 16-Blt Circuit
Name Version Version Bytes Bytes Timers Type
8051 8031 - 4K 128 2 HMOS
8051AH 8031AH - 4K 128 2 HMOS
80C51BH 80C31BH 87C51BH 4K 128 2 CHMOS
8052AH 8032AH - 8K 256 3 HMOS
83C451 80C451 87C451 4K 128 2 CHMOS
83C552 80C552 87C552 8K 256 3 CHMOS
83C652 80C652 87C652 8K 256 2 CHMOS
83C751 - 87C751 2K 64 1 CHMOS
83C752 - 87C752 2K 64 1 CHMOS
February 1989 1-1

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TXD RXD
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(63C552)
o
,PO P2, P1 P3 P~P5-P8
01
-L
FIXED RATEj •
ADDRESS/DATA
TIMER ~
(83C751/2) NOTES:
Po-P3 FOR 8051. 8052. 83C852
3
Po-P5 FOR 83C552 '<
PO-P6 FOR 83C451
PART OF PO. AND Pl. P3 FOR 83C75l AND 83C752
2
CD
c
~en-
<
~.
G)
c:
a:CD
Signetics Microprocessor Products User's Guide
Section 1 8051 Family Overview
83C552 • 19 I/O lines

• Single level interrupt structure
The 83C552 is an extended function 80C51 with the • One counter/timer with 16-bit autoload
following features: • No external memory expand ability (data memory can
be expanded using the I2C serial port and I2C com-
• 8k bytes of ROM patible memory devices).
• 256 bytes of RAM
• lO-bit 8 channel AID Note that since there is no external expandability, the
• Counter/timer array with high speed outputs and cap- external memory addressing signals: WR, RD, PSEN,
ture inputs EA, and ALE are not present. Because of. these differ-
• 4 counter/timers (including a watchdog timer) ences, instructions UMP, LCALL, and MOVX have no
• 2 PWM outputs meaning.
• 2 serial ports
• 6 8-bit I/O ports For all other instructions the 83C751 is 100% code
• I2C serial port compatible with the 80CS1 and operates at full 80CS1
• 68-pin PLCC package speed.
The 83C552 is 100% code compatible with the 80C5l. The EPROM version of the 83C751 is the 87C75l.
The ROMless version of the 83C552 is the 80C552 and
the EPROM version is the 87C552. 83C752
83C652 The 83C752 is a derivative version of the 80C51 that is

intended for use in automotive, electro-mechanical, and
The 83C652 is an 80C51 with the following additions: an consumer applications. The emphasis of the device is on
8k ROM, 256 bytes RAM and I2C serial port. high integration and small packaging. The 83C752 con-
tains most of the features of the 80C51 with the following
The 83C652 is pin-for-pin compatible with the 80C51 exceptions:
except for minor DC specifications on the l2C serial
port pins. • 2K bytes ROM
• 64 bytes RAM
The ROMless version of the 83C652 is the 80C652. • Single level interrupt structure
• One 16-bit counter/timer. (mode 2 only) with 16-bit
83C751 autoload
• Two 8-bit and one 5-bit bidirectional I/O ports
The 83C751 is a 24-pin version of the 80C51, where • I2C serial interface
small size and cost are of· prime consideration. The • One PWM with timer, including overflow interrupt
83C751 is packaged in a 24-pin "skinnydip" (.300 wide) capability
and in a 28-pin PLCC package. • 5 channels of 8-bit AID
• 28-pin packages, .both DIP and SMD
The following differences exist between the 83C751 and
the 80C5l. The 83C751 has: The 83C752 does not have external memory expand-
ability. The EPROM versions of the 83C752 is the
• 2K bytes ROM 87C752.
• 64 bytes RAM
• I2C serial port (no UART)
Table 2. 80C51 Derivative Comparisons

Device AID Ports PWM Timers UART
80C51 - 4 - Two standard Standard
83C451 - 7 - Two standard Standard
83C552 8 channel/ 6 2 Two standard, Standard, 12C
10 bit timer 2,
watchdog
(4 total)
83C652 - 4 - Two standard Standard, 12C
83C751 - 2-3/8 - One standard, 12C
extended to
16-bit autoload
83C752 5 channel/ 2-5/8 1 One standard, 12C
8 bit extended to
16-bit autoload
February 1989 1-3

Section 1 8051 Family Architecture
8051 ARCHITECTURE 8051 FAMILY DEVICES

MEMORY ORGANIZATION
MEMBERS OF THE FAMILY
All 8051 devices have separate address spaces for pro-
The basic architecture of the 8051 devices is as follows: gram and data memory, as shown in Figure 3. The
logical separation of program and data memory allows
8051 the data memory to be accessed by 8-bit addresses,
which can be more quickly stored and manipulated by an
The 8051 is the original member of the family (see 8-bit CPU. Nevertheless, 16-bit data memory addresses
Figure 2). Among the features of the 8051 are: can also be generated through the DPTR register.
• 8-bit CPU optimized for control applications Program memory can only be read, not written to.
• Extensive Boolean processing (single-bit logic) There can be up to 64K bytes of program memory. In
capabilities the 8051, 8051AH, 80C51BH, and their EPROM ver-
• 32 bi-directional and individually addressable I/O lines sions, the lowest 4K bytes of program memory are on-
• 128 bytes of on-chip data RAM chip. In the ROMless versions (8031, 8031AH,
• Two 16-bit timer/counters 80C31BH) all program memory is external. The read
• Full duplex UART strobe for external program memory is the !'SEN (pro-
• 5 source interrupt structure with 2 priority levels gram store enable).
• On-chip clock oscillator
• 4K bytes of on-chip program memory Data Memory occupies a separate address space from
• 64K program memory address space Program Memory. Up to 64K bytes of external RAM can
• 64K data memory address space be addressed in the external Data Memory space.. The
CPU generates read and write signals, RD and WR, as
The 8031 differs from the 8051 in not having the on-chip needed during external Data Memory accesses.
program ROM. Instead, the 8031 fetches all instructions
from external memory. External Program Memory and external Data Memory
may be combined if desired by applying the RD and
8051AH PSEN signals to the inputs of an AND gate and using
the output of the gate as the read strobe to the external
The 8051AH is identical to the 8051, but is fabricated Program/Data memory.
with HMOS II technology. It is pin-for-pin compatible
with the 8051. The ROMless version of the 8051AH is PROGRAM MEMORY
the 8031AH.
Figure 4 shows a map of the lower part of the Program
8OC51BH Memory. After reset, the CPU begins execution from
location OOOOH. As shown in Figure 4, each interrupt is
The 80C5IBH is the CHMOS version of the 8051. assigned a fixed location in Program Memory. The inter-
Functionally, it is fully compatible with the 8051, but rupt causes the CPU to jump to that location, where it
being CMOS it draws less current than the HMOS commences execution of the service routine. External
counterpart. To further exploit the power savings avail- Interrupt 0, for example, is assigned to location 0003H.
able in CMOS circuitry, two reduced power modes are If External Interrupt 0 is going to be used, its service
added: routine must begin at location 0003H. If the interrupt is
not going to be used, its service location is available as
1. Software-invoked idle mode, during which the CPU general purpose Program Memory.
is turned off while the RAM and other on-chip pe-
ripherals continue operating. In this mode, current The interrupt service locations are spaced at 8-byte
draw is reduced to about 15% of the current drawn intervals: 0003H for External Interrupt 0, OOOBH for
when the device is fully active. Timer 0, 0013H for External Interrupt 1, 00IBH for
2. Software-invoked power down mode, during which all Timer 1, etc. If an interrupt service routine is short
on-chip activities are suspended. The on-chip RAM enough (as is often the case in control applications), it
continues to hold its data. In this mode the device can reside entirely within that 8-byte interval. Longer
typically draws less than 1O~. service routines can use a jump instruction to skip over
subsequent interrupt locations, if other interrupts are in
Although the 80C51BH is functionally compatible with its use.
HMOS counterpart, specific differences between the two
types of devices must be considered in the design of an The lowest 4K bytes of Program Memory can either be
application circuit if one wishes to ensure complete in the on-chip ROM or in an external ROM. This
interchangeability between the HMOS and CHMOS de- selection is made by strapping the EA (External Access)
vices. The ROMless version of the 80C51BH is the pin to either Vee, or Vss.
80C3IBH. The EPROM version is the 87C51.
February 1989 1-4

EXTERNAL
INTERRUPTS
128 COUNTER
RAM INPUTS
TXD RXD
,!O
.
ADDRESS/DATA
P2, PI P3
Figure 2. 8051 Block Diagram
PROGRAM MEMORY
(READ ONLY)
_________ DATA MEMORY
J!~2~~~~~ ________ _
.------------------------
• FFFFH: , . . - - -... FFFFH: r----,
EXTERNAL
INTERNAL
FFH:~------I""'"'';;'''--'
••
EA=O
EXTERNAL
EA=!
INTERNAL
••
00 _ _ __
....."'T'.....I~OOOO -+11-.._.....1 OOOO""~-r"
._-------------------
Figure 3. 8051 Memory Structure
February 1989 1-5

In the 8051, if the EA pin is strapped to Vcc, then the

program fetches to addresses OOOOH through OFFFH are
directed to the internal ROM. Program fetches to ad-
dresses 1000H through FFFFH are directed to external
ROM.
002BH
If the EA pin is strapped to Vss, then all program
fetches are directed to external ROM. The ROMless 0023H
parts (8031, 80C31, etc .. ) must have this pin externally
INTERRUPT
strapped to Vss to enable them to execute from external LOCATIONS 00lBH]
Program Memory. 8 BYTES
0013H
The read strobe to external ROM, PSEN, is used for all
OOOBH
external program fetches. PSEN is not activated for
internal program fetches.
The hardware configuration for external program execu-

tion is shown in Figure 5. Note that 16 I/O lines (Ports
_
...... .......
0003H
OOOOH
o and 2) are dedicated to bus functions during external Figure 4. 8051 Program Memory
Program Memory fetches. Port 0 (PO in Figure 5) serves
as a multiplexed address/data bus. It emits the low byte
of the Program Counter (PCL) as an address, and then
goes into a float state awaiting the arrival of the code
byte from the Program Memory. During the time that
the low byte of the Program Counter is valid on Port 0,
the signal ALE (Address Latch Enable) clocks this byte 8051 EPROM
into an address latch. Meanwhile, Port 2 (P2 in Figure
5) emits the high byte of the Program Counter (PCH).
Then PSEN strobes the EPROM and the code byte is
read into the microcontroller.
LATCH
Program Memory addresses are always 16 bits wide,
even though the actual amount of Program Memory used
may be less than 64K bytes. External program execution P21======~
sacrifices two of the8-bit ports, PO and P2, to the
function of addressing the Program Memory.
DATA MEMORY Figure 5. Executing from External

Program Memory
The right half of Figure 3 shows the internal and exter-
nal Data Memory spaces available to the 8051 user.
Figure 6 shows a hardware configuration for accessing
up to 2K bytes of external RAM. The CPU in this case
is executing from internal ROM. Port 0 serves as a
multiplexed address/data bus to the RAM, and 3 lines of
Port 2 are being used to page the RAM. The CPU
generates RD and WR signals as needed during external
RAM accesses. There can be up to 64K bytes of exter-
nal Data Memory. External Data Memory addresses can
be either 1 or 2 bytes wide. One-byte addresses are
often used in conjunction with one or more other I/O
lines to page the RAM, as shown in Figure 6.
Two-byte addresses can also be used, in which case the

high address byte is emitted at Port 2.
Internal Data Memory is mapped in Figure 7. The Figure 6. Accessing External Data Memory.
memory space is shown divided into three blocks, which If the Program Memory is Internal, the other
are generally referred to as the Lower 128, the Upper
Bits of P2 are Available as 110
128, and SFR space.
February 1989 1-6

7rH
rrH ·--------r----, rrH

: ACCESSIBLE ACCESSIBLE
UPPER ,BY INDIRECT BANK 2rH
BY DIRECT
128 'ADDRESSING SELECT T-ADDRESSABLE SPACE
ADDRESSING } BI
BITS IN {B IT ADDRESSES 0-7r)
BOH: ONLY
BOH PSW~ 20H
7rH
ACCESSIBLE lrH
~
LOWER BY DIRECT " ' - SPECIAL } PORTS { 18H
11
12B AND INDIRECT rUNCTION STATUS AND
17H
ADDRESSING REGISTERS CONTROL BITS 10 { BANKS or
0'--_ _--' 10H
TIMER REGISTERS
OrH
REGISTERS 01 { O-R7
STACK POINTER OBH
ACCUMULATOR 07H RESET VALUE or
(ETC.)
00 {0 STACK POINTER
Figure 7. Internal Data Memory Figure 8. Lower 128 Bytes of Internal RAM
Internal Data Memory addresses are always one byte

wide, which implies an address space of only 256 bytes.
However, the addressing modes for internal RAM can in
fact accommodate 384 bytes, using a simple trick. Di- rrH
rect addresses higher than 7FH access one memory
space, and indirect addresses higher than 7FH access a
different memory space. Thus Figure 7 shows the Upper
128 and SFR space occupying the same block of ad- NO BIT-ADDRESSABLE
SPACES
dresses, 80H through FFH, although they are physically
separate entities.
The Lower 128 bytes of RAM are present in all 8051

devices as mapped in Figure 8. The lowest 32 bytes are
grouped into 4 banks of 8 registers. Program instructions
call out these registers as RO through R7. Two bits in
the Program Status Word (PSW) select which register BOH
bank is in use. This allows more efficient use of code
space, since register instructions are shorter than in-
structions that use direct addressing. Figure 9. Upper 128 Bytes of Internal RAM
The next 16 bytes above the register banks form a block
of bit-addressable memory space. The 8051 instruction
set includes a wide selection of single-bit instructions,
and the 128 bits in this area can be directly addressed
rrH
· REGISTER-MAPPED PORTS
EOH ACC
by these instructions. The bit addresses in this area are ADDRESSES THAT END IN
OOH through 7FH.
All of the bytes in the Lower 128 can be accessed by BOH

··
PORT 3
OH OR 8H ARE ALSO
BIT-ADDRESSABLE
either direct or indirect addressing. The Upper 128 -PORT PINS

(Figure 9) can only be accessed by indirect addressing.
AOH
·
PORT 2
-ACCUMULATOR
-PSW
{ETC.}
Figure 10 gives a brief look at the Special Function
Register (SFR) space. SFRs include the Port latches, 90H PORT 1
timers, peripherals controls, etc. These registers can
only be accessed by direct addressing. Sixteen addresses
in SFR space are both byte- and bit-addressable. The
bit-addressable SFRs are those whose address ends in BOH
·
PORT 0
OH or 8H. The bit addresses in this area are 80H

through FFH.
Figure 10. SFR Space
February 1989 1-7

8051 FAMILY INSTRUCTION SET ADDRESSING MODES

The 8051 instruction set is optimized for 8-bit control The addressing modes in the 8051 instruction set are as
applications. It provides a variety of fast addressing follows:
modes for accessing the internal RAM to facilitate byte
operations on small data structures. The instruction set DIRECT ADDRESSING
provides extensive support for one-bit variables as a
separate data type, allowing direct bit manipulation in In direct addressing the operand is specified by an 8-bit
control and logic systems that require Boolean proc- address field in the instruction. Only internal Data RAM
essing. and SFRs can be directly addressed.
PROGRAM STATUS WORD INDIRECT ADDRESSING
The Program Status Word (PSW) contains several status In indirect addressing the instruction specifies a register
bits that reflect the current state of the CPU. The PSW, which contains the address of the operand. Both internal
shown in Figure 11, resides in SFR space. It contains and external RAM can be indirectly addressed.
the Carry bit, the Auxiliary Carry (for BCD operations),
the two register bank select bits, the Overflow flag, a The address register for 8-bit addresses can be RO or
Parity bit, and two user-definable status flags. R1 of the selected bank, or the Stack Pointer. The
address register for 16-bit addresses can only be the 16-
The Carry bit, other than serving the function of a Carry bit "data pointer" register, DPTR.
bit in arithmetic operations, also serves as the "Accumu-
lator" for a number of Boolean operations. REGISTER INSTRUCTIONS
The bits RSO and RS1 are used to select one of the four The register ·banks, containing registers RO through R7,
register banks shown in Figure 8. A number of instruc- can be accessed by certain instructions which carry a 3-
tions refer to these RAM locations as RO through R7. bit register specification within the opcode of the in-
The selection of which of the four is being referred to is struction. Instructions that access the registers this way
made on the basis of the RSO and RS1 at execution are code efficient, since this mode eliminates an address
time. byte. When the instruction is executed, one of the eight
registers in the selected bank is accessed. One of four
The Parity bit reflects the number of 1s in the Accumu- banks is selected at execution time by the two bank
lator: P = 1 if the Accumulator contains an odd number select bits in the PSW.
of 1s, and P = 0 if the Accumulator contains an even
number of 1s. Thus the number of 1s in the Accumulator REGISTER-SPECIFIC INSTRUCTIONS
plus P is always even. Two bits in the PSW are un-
committed and may be used as general purpose status Some instructions are specific to a certain register. For
flags. example, some instructions always operate on the Accu-
mulator, or Data Pointer, etc., so no address byte is
needed to point to it. The opcode itself does that.
Instructions that refer to the Accumulator as A assemble
as accumulator specific opcodes.
I CY I AC I fO I RS,j Rsol OV I I P I
PSW 7 J L PSW 0
CARRY fLAG RECEIVES CARRY OUT PARITY Of ACCUWULATOR SET
fROW BIT 7 Of AlU OPERANDS BY HARDWARE TO 1 If IT CONTAINS
AN ODD NUWBER Of 1S. OTHERWISE
IT IS RESET TO 0
.-
PSW 6
AUXilIARY CARRY fLAG RECEIVES
' - - - PSW 1
USER DEfiNABLE fLAG
CARRY OUT fROW BIT 3 Of
ADDITION OPERANOS
PSW 5 PSW 2
GENERAL PURPOSE STATUS fLAG OVERflOW fLAG SET BY
ARITHWETIC OPERATIONS
PSW 4 PSW 3
REGISTER BANK SELECT BIT 1 REGISTER BANK SELECT BIT 0
Figure 11. PSW (program Status Word) Register in 8051 Devices
February 1989 1-8

IMMEDIATE CONSTANTS ARITHMETIC INSTRUCTIONS

The value of a constant can follow the ope ode in Pro- The menu of arithmetic instructions is listed in Table J.
gram Memory. For example, The table indicates the addressing modes that can be
used with each instruction to access the <byte> oper-
MOV A, #100 and. For example, the ADD A,<byte> instruction can
be written as:
loads the Accumulator with the decimal number 100.
TIle same number could be specified in hex digits as ADD A, 7FH (direct addressing)
64H. ADD A, @RO (indirect addressing)
ADD A, R7 (register addressing)
INDEXED ADDRESSING ADD A, #127 (immediate constant)
Only program Memory can be accessed with indexed The execution times listed in Table J assume a 12MHz
addressing, and it can only be read. TIlis addressing clock frequency. All of the arithmetic instructions exe-
mode is intended for reading look-up tables in Program cute in If15 except the INC DPTR instruction, which
Memory. A 16-bit base register (either DPTR or the takes 2f15, and the Multiply and Divide instructions,
Program Counter) points to the base of the table, and which take 4f15.
the Accumulator is set up with the table entry number.
The address of the table entry in Program Memory is Note that any byte in the interual Data Memory space
formed by adding the Accumulator data to the base can be incremented without going through the Accumu-
pointer. lator.
Another type of indexed addressing is used in the "case One of the INC instructions operates on the 16-bit Data
jump" instruction. In this case the destination address of Pointer. The Data Pointer is used to generate 16-bit
a jump instruction is computed as the sum of the base addresses for external memory, so being able to incre-
pointer and the Accumulator data. ment it in one 16-bit operation is a useful feature.
Table 3. 8051 Arithmetic Instructions
Addressing Modes Execution

Mnemonic Operation
Ind Reg Imm Time (ILS)
Dir
ADD A.<byte> A = A + <byte> X X X X 1
ADDC A, <byte> A = A + <byte> + C X X X X 1
SUBB A, <byte> A = A - <byte> - C X X X X 1
INC A A=A+1 Accumulator only 1
INC <byte> <byte> = <byte> + 1 X X X 1
INC DPTR DPTR = DPTR + /1 Data Pointer only 2
DEC A A=A-1 Accumulator only 1
DEC <byte> <byte> = <byte> - 1 X X X 1
MUL AB B:A = BxA ACC and B only 4
DIV AB A = Int [AlB] 4
ACC and B only
B = Mod [AlB)
DA A Decimal Adjust Accumulator only 1
February 1989 1-9

The MUL AB instruction multiplies the Accumulator by ANL A, <byte>

the data in the B register and puts the l6-bit product
into the concatenated B and Accumulator registers. will leave the Accumulator holding OOOlOOOlB.
The DIV AB instruction divides the Accumulator by the The addressing modes that can be used to access the
data in the B register and leaves the 8-bit quotient in the <byte> operand are listed in Table 4.
Accumulator, and the 8-bit remainder in the B register.
The ANL A, <byte> instruction may take any of the
Oddly enough, DIV AB finds less use in arithmetic forms:
"divide" routines than in radix conversions and program-
mable shift operations. An example of the use of DIV ANL A,7FH (direct addressing)
AB in a radix conversion will be given later. In shift ANL A,@Rl (indirect addressing)
operations, dividing a number by 2n shifts its n bits to ANL A,R6 (register addressing)
the right. Using DIV AB to perform the division com- ANL A,#53H (immediate constant)
pletes the shift in 4j.1S and leaves the B register holding
the bits that were shifted out. The DA A instruction is All of the logical instructions that are Accumulator-
for BCD arithmetic operations. In BCD arithmetic, specific execute in lj.lS (using a 12MHz clock). The
ADD and ADDC instructions should always be followed others take 2j.1S.
by a DA A operation, to ensure that the result is also in
BCD. Note that DA A will not convert a binary number Note that Boolean operations can be performed on any
to BCD. The DA A operation produces a meaningful byte in the internal Data Memory space without going
result only as the second step in the addition of two BCD through the Accumulator. The XRL <byte>, #data in-
bytes. struction, for example, offers a quick and easy way to
invert port bits, as in XRL PI, #OFFH.
LOGICAL INSTRUCTIONS
If the operation is in response to an interrupt, not using
Table 4 shows the list of 8051 logical instructions. The the Accumulator saves the time and effort to stack it in
instructions that perform Boolean operations (AND, OR, the service routine.
Exclusive OR, NOT) on bytes perform the operation on a
bit-by-bit basis. That is, if the Accumulator contains The Rotate instructions (RL A, RLC A, etc.) shift the
OOllOlOlB and byte contains OlO]OOl1B, then: Accumulator 1 bit to the left or right. For a left
rotation, the MSB rolls into the LSB position. For a
right rotation, the LSB rolls into the MSB position.
Table 4. 8051 Logical Instructions
Mnemonic Addressing Modes Execution

Operation Time (p.s)
Dlr Ind Reg Imm
ANL A,<byte> A = A .AND. <byte> X X X X 1
ANL <byte> ,A <byte> = <byte>.AND.A X 1
ANL <byte> , # data <byte> = <byte> .AND. #data X 2
ORL A,<byte> A = A .OR. <byte> X X X X 1
ORL <byte> ,A <byte> = <byte> .OR.A X 1
ORL <byte>,#data <byte> = <byte> .OR. #data X 2
XRL A,<byte> A = A .XOR. <byte> X X X X 1
XRL <byte> ,A <byte> = <byte>.XOR.A X 1
XRL < byte> , # data <byte> = <byte>.XOR.#data X 2
CRL A A = OOH Accumulator only 1
CPL A A = .NOT.A Accumulator only 1
RL A Rotate ACC Left 1 bit Accumulator only 1
RLC A Rotate Left through Carry Accumulator only 1
RR A Rotate ACC Right 1 bit Accumulator only 1
RRC A Rotate Right through Carry Accumulator only 1
SWAP A Swap Nibbles in A Accumulator only 1
February 1989 1-10

The SWAP A instruction interchanges the high and low TIle Upper 128 are not implemented in the 8051,
nibbles within the Accumulator. This is a useful opera- 8051AH, or 80C51BH, nor in their ROMless or EPROM
tion in BCD manipulations. For example, if the Accu- counterparts. With these devices, if the SP points to the
mulator contains a binary number which is known to be Upper 128, PUSHed bytes are lost, and POPed bytes
less than 100, it can be quickly converted to BCD by the are indeterminate.
following code:
The Data Transfer instructions include a 16-bit MOV
MOV B,#lO that can be used to initialize the Data Pointer (DPTR)
DIV AB for look-up tables in Program Memory, or for 16-bit
SWAP A external Data Memory accesses.
ADD A,B
The XCH A, <byte> instruction causes the Accumula-
Dividing the number by 10 leaves the tens digit in the tor and addressed byte to exchange data. The XCHD A,
low nibble of the Accumulator, and the ones digit in the @Ri instruction is similar, but only the low nibbles are
B register. TIle SWAP and ADD instructions move the involved in the exchange.
tens digit to the high nibble of the Accumulator, and the
ones digit to the low nibble. To see how XCH and XCHD can be used to facilitate
data manipulations, consider first the problem of shifting
DATA TRANSFERS an 8-digit BCD number two digits to the right. Figure
12 shows how this can be done using direct MOVs, and
INTERNAL RAM for comparison how it can be done using XCH instruc-
tions. To aid in understanding how the code works, the
Table 5 shows the menn of instructions that are avail- contents of the registers that are holding the BCD
able for moving data around within the internal memory number and the content of the Accumulator are shown
spaces, and the addressing modes that can be used with alongside each instruction to indicate their status after
each one. With a 12MHz clock, all of these instructions the instruction has been executed.
execute in either 1 or 2)lS.
After the routine has been executed, the Accumulator
The MOV <dest>, <src> instruction allows data to be contains the two digits that were shifted out on the right.
transferred between any two internal RAM or SFR loca- Doing the routine ,vith direct MOVs uses 14 code bytes
tions without going through the Accumulator. Remember and 9)lS of execution time (assuming a 12MHz clock).
the Upper 128 byes of data RAM can be accessed only The same operation with XCHs uses less code and exe-
by indirect addressing, and SFR space only by direct cutes almost twice as fast.
addressing.
To right-shift by an odd number of digits, a one-digit
Note that in all 8051 devices, the stack resides in on- shift must be executed.
chip RAM, and grows upwards. The PUSH instruction
first increments the Stack Pointer (SP), then copies the Figure 13 shows a sample of code that will right-shift a
byte into the stack. PUSH and POP use only direct ad- BCD number one digit, using the XCHD instruction.
dressing to identify the byte being saved or restored, but Again, the contents of the registers holding the number
the stack itself is accessed by indirect addressing using and of the Accumulator are shown alongside each in-
the SP register. TIlis means the stack can go into the struction.
Upper 128, if they are implemented, but not into SFR
space.
Table 5. Data Transfer Instructions that Access Internal Data Memory Space

Mnemonic Operation
Reg Time (/-Ls)
Dir Ind Imm
MOV A,<src> A= <src> X X X X 1
MOV <dest>,A <dest> =A X X X 1
MOV <dest>, <src> <dest> = <src> X X X X 2
MOV DPTR,#data16 DPTR = 16-bit immediate constant. X 2
PUSH <src> INC SP: MOV "@SP",<src> X 2
POP <dest> MOV <dest>, "@SP" : DEC SP X 2
XCH A, <byte> ACC and < byte> exchange data X X X 1
XCHD A,@Ri ACC and @Ri exchange low nibbles X 1
February 1989 1-11

EXTERNAL RAM
Table 6 shows a list of the Data Transfer instructions

that access external Data Memory. Only indirect ad-
dressing can be used. The choice is whether to use a
2A 2B 2C 20 2E ACC one-byte address, @Ri, where Ri can be either RO or
MOV A,2EH 00 12 34 56 78 78 Rl of the selected register bank, or a two-byte address,
MOV 2EH,20H 00 12 34 56 56 78 @DPTR. The disadvantage to using 16-bit addresses if
MOV 20H,2CH 00 12 34 34 56 78
MOV 2CH,2BH 00 only a few K bytes of external RAM are involved is that
12 12 34 56 78
MOV 2BH,#0 00 00 12 34 56 78 16-bit addresses use all 8 bits of Port 2 as address bus.
(a) Using direct MOVs: 14 bytes, 9 /Ls On the other hand, 8-bit addresses allow one to address
a few bytes of RAM, as shown in Figure 6, without hav-
2A 2B 2C 20 2E ACC ing to sacrifice all of Port 2. All of these instructions
CLR A 00 12 34 56 78 00 execute in 2iJS, with a 12MHz clock.
XCH A,2BH 00 00 34 56 78 12
XCH A,2CH 00 00 12 56 78 34 Table 6. 8051 Data Transfer Instructions that
XCH A,20H 00 00 12 34 78 56 Access External Data Memory Space
XCH A,2EH 00 00 12 34 56 78
(b) Using XCHs: 9 bytes, 5 "'S Address Execution
MnemoniC Operation
Width Time (",s)
Figure 12. Shifting a BCD Number Read external
8 bits MOVXA,@Ri 2
RAM@Ri
Two Digits to the Right
Write external
8 bits MOVX@Ri,A RAM@Ri 2
Read external
16 bits MOVXA,@OPTR 2
RAM@DPTR
Write external
16 bits MOVX @DPTR,A 2
RAM@DPTR
MOV Rl,#2EH Note that in all external Data RAM accesses, the Ac-
MOV RO,#2DH
cumulator is always either the destination or source of
loop for R1 = 2EH: the data.
LOOP: MOV A,@Rl 00 12 34 56 78 78
XCHD A,@RO 00 12 34 58 78 76 The read and write strobes to external RAM are acti-
SWAP A 00 12 34 58 78 67 vated only during the execution of a MOVX instruction.
MOV @R1,A 00 12 34 58 67 67 Normally these signals are inactive, and in fact if
DEC R1 00 12 34 58 67 67 they're not going to be used at all, their pins are avail-
DEC RO 00 12 34 58 67 67 able as extra I/O lines. More about that later.
CJNE R1,#2AH,LOOP
:~~~:~~=~ : 2BH:
loop for R1
~g~;
=
Iggl ~~I~~I:~I~~I ~~
08 01 23 45 67 01
LOOKUP TABLES
Table 7 shows the two instructions that are available for

reading lookup tables in Program Memory. Since these
CLR A 108101 1231451671 00
XCH A,2AH 00 01 23 45 67 08 instructions access only Program Memory, the lookup
tables can only be read, not updated.
Figure 13. Shifting a BCD Number
One Digit to the Right If the table access is to external Program Memory, then
the read strobe is PSEN.
First, pointers Rl and RO are set up to point to the two
bytes containing the last four BCD digits. 'Then a loop is Table 7. 8051 Lookup Table Read Instructions
executed which leaves the last byte, location 2EH, hold-
Mnemonic Operation Execution
ing the last two digits of the shifted number. The point- Time (/La)
ers are decremented, and the loop is repeated for loca-
MOVC A,@A+DPTR Read Pgm Memory 2
tion 2DH. The CJNE instruction (Compare and Jump if at (A+DPTR)
Not Equal) is a loop control that will be described later.
MOVC A,@A+PC Read Pgm Memory 2
The loop executed from LOOP to CJNE for Rl = 2EH,
at (A+PC)
2DH, 2CH and 2BH. At that point the digit that was
originally shifted out on the right has propagated to lo-
cation 2AH. Since that location should be left with Os,
the lost digit is moved to the Accumulator.
February 1989 1-12

TIle mnemonic is MOVC for "move constant". 11,e first Table 8. 8051 Boolean Instructions
MOVC instruction in Table 7 can accommodate a table
of up to 256 entries numbered 0 through 255. 11,e Execution
Mnemonic Operation
Time (f£8)
number of the desired entry is loaded into the Accumu-
lator, and the Data Pointer is set up to point to begin- ANL C,bit C = C .AND. bit 2
ning of the table. Then: ANL C,Ibit C = C .AND .. NOT. bit 2
ORL C,bit C = C.OR.bit 2
MOVC A,@A+DPTR
ORL C,Ibit C = C .OR. .NOT. bit 2
copies the desired table entry into the Accumulator. MOV C,bit C = bit 1
MOV bit,C bit = C 2
The other MOVC instruction works the same way, ex-
CLR C C=O 1
cept the Program Counter (PC) is used as the table
base, and the table is accessed through a subroutine. CLR bit bit =0 1
First the number of the desired entry is loaded into the SETB C C-l 1
Accumnlator, and the subroutine is called: SETB bit bit = 1 1
MOV A, ENTRY NUMBER CPL C C = .NOT.C 1
CALL TABLE CPL bit bit = .NOT. bit 1
JC rei Jump if C = 1 2
The subroutine "TABLE" would look like this:
JNC rei JumpifC = 0 2
TABLE: MOVC A,@A+PC JB bit,rel Jump if bit =1 2
RET JNB bit, rei Jump if bit =0 2
The table itself immediately follows the RET (return)

JBC bit,rel Jump if bit = 1; CLR bit 2
instruction in Program Memory. This type of table can
have up to 255 entries, numbered 1 through 255. The Carry bit in the PSW is used as the single-bit
Number 0 cannot be used, because at the time the Accnmnlator of the Boolean processor. Bit instructions
MOVC instruction is executed, the PC contains the ad- that refer to the Carry bit as C assemble as Carry-
dress of the RET instruction. An entry numbered 0 specific instructions (CLR C, etc). The Carry bit also
would be the RET ope ode itself. has a direct address, since it resides in the PSW regis-
ter, which is bit-addressable.
BOOLEAN INSTRUCTIONS
Note that the Boolean instruction set includes ANL and
8051 devices contain a complete Boolean (single-bit) ORL operations, but not the XRL (Exclusive OR) opera-
processor. The internal RAM contains 128 addressable tion. An XRL operation is simple to implement in soft-
bits, and the SFR space can support up to 128 other ad- ware. Suppose, for example, it is required to form the
dressable bits. All of the port lines are bit-addressable, Exclusive OR of two bits:
and each one can be treated as a separate single-bit
port. The instructions that access these bits are not just C = bill .XRL. bit2
conditional branches, but a complete menu of move, set,
clear, complement, OR, and AND instructions. These The software to do that could be as follows:
kinds of bit operations are not easily obtained in other
architectures with any amount of byte-oriented software. MOV C,bill
JNB bit2,OVER
The instruction set for the Boolean processor is shown in CPL C
Table 8. All bit accesses are by direct addressing. OVER: (continue)
Bit addresses OOH throngh 7FH are in the Lower 128, First, bill is moved to the Carry. If bit2 = 0, then C
and bit addresses 80H throngh FFH are in SFR space. now contains the correct result. That is, bill .XRL. bit2
= bill if bit2 = O. On the other hand, if bit2 = 1, C now
Note how easily an internal flag can be moved to a port contains the complement of the correct result. It need
pin: only be inverted (CPL C) to complete the operation.
MOV C,FLAG This code uses the JNB instruction, one of a series of
MOV Pl.O,C bit-test instructions which execute a jump if the ad-
dressed bit is set (JC, ID, mC) or if the addressed bit
In this example, FLAG is the name of any addressable is not set (JNC, JNB). In the above case, bit2 is being
bit in the Lower 128 or SFR space. An I/O line (the tested, and if bit2 = 0 the CPL C instruction is jumped
LSB of Port 1, in this case) is set or cleared depending over.
on whether the flag bit is 1 or O.
February 1989 1-13

mc executes the jump if the addressed bit is set, and an 11-bit constant. The instruction is 2 bytes long, con-
also clears the bit. Thus a flag can be tested and sisting of the opcode, which itself contains 3 of the 11
cleared in one operation. address bits, followed by another byte containing the low
8 bits of the destination address. When the instruction is
All the PSW bits are directly addressable, so the Parity executed, these 11 bits are simply substituted for the low
bit, or the general purpose flags, for example, are also 11 bits in the Pc. The high 5 bits stay the same. Hence
available to the bit-test instructions. the destination has to be within the same 2K block as
the instruction following the NMP.
RELATIVE OFFSET
In all cases the programmer specifies the destination
The destination address for these jumps is specified to address to the assembler in the same way: as a label or
the assembler by a label or by an actual address in Pro- as a 16-bit constant. The assembler will put the destina-
gram memory. However, the destination address as- tion address into the correct format for the given instruc-
sembles to a relative offset byte. This is a signed (two's tion. If the format required by the instruction will not
complement) offset byte which is added to the PC in support the distance to the specified destination address,
two's complement arithmetic if the jump is executed. a "Destination out of range" message is written into the
List file.
The range of the jump is therefore -128 to + 127 Pro-
gram Memory bytes relative to the first byte following The JMP @A+DPTR instruction supports case jumps.
the instruction. The destination address is computed at execution time as
the sum of the 16-bit DPTR register and the Accumula-
JUMP INSTRUCTIONS tor. Typically, DPTR is set up with the address of a
jump table, and the Accumulator is given an index to the
Table 9 shows the list of unconditional jumps with execu- table. In a 5-way branch, for example, an integer 0
tion time for a 12MHz clock. through 4 is loaded into the Accumulator. The code to
be executed might be as follows:
Table 9. Unconditional Jumps in 8051 Devices
Execution
MOV DPTR,#JUMP TABLE
Mnemonic Operation MOV A,INDEx..NUMBER
Time (I£S)
RL A
JMP addr Jump to addr 2 JMP @A+DPTR
JMP @A+DPTR Jump to A + DPTR 2
CALL addr Call subroutine at addr 2 The RL A instruction converts the index number (0
through 4) to an even number on the range 0 through 8,
RET Return from subroutine 2 because each entry in the jump table is 2 bytes long:
RETI Return from interrupt 2
NOP No operation
JUMP TABLE:
1
NMP CASE 0
AJMP CASE 1
AJMP CASE 2
AJMP CASE 3
AJMP CASE 4
The Table lists a single "JMP addr" instruction, but in
Table 9 shows a single "CALL addr" instruction, but
fact there are three SJMP, LJMP and NMP, which dif-
there are two of them, LCALL and ACALL, which differ
fer in the format of the destination address. JMP is a
in the format in which the subroutine address is given to
generic mnemonic which can be used if the programmer
the CPU. CALL is a generic mnemonic which can be
does not care which way the jump is encoded.
used if the programmer does not care which way the ad-
The SJMP instruction encodes the destination address as dress is encoded.
a relative offset, as described above. The instruction is 2
The LCALL instruction uses the 16-bit address format,
bytes long, consisting of the opcode and the relative off-
and the subroutine can be anywhere in the 64K Program
set byte. The jump distance is limited to a range of -128
Memory space. The ACALL instruction uses the ll-bit
to +127 bytes relative to the instruction following the
SJMP. format, and the subroutine must be in the same 2K block
as the instruction following the ACALL.
The LJMP instruction encodes the destination address as
In any case the programmer specifies the subroutine ad-
a 16-bit constant. The instruction is 3 bytes long, con-
dress to the assembler in the same way: as a label or as
sisting of the opcode and two address bytes. The destina-
a 16-bit constant. The assembler will put the address in-
tion address can be anywhere in the 64K Program Mem-
ory space. to the correct format for the given instructions.
Subroutines should end with a RET instruction, which re-

The NMP instruction encodes the destination address as
turns execution to the instruction following the CALL.
February 1989 1-14

RETI is used to return from an interrupt service routine. CPU TIMING

The only difference between RET and RETI is that
RETI tells the interrupt control system that the interrupt All 8051 microcontrollers have an on-chip oscillator
in progress is done. If there is no interrupt in progress which can be used if desired as the clock source for the
at the time RETI is executed, then the RETI is func- CPU. To use the on-chip oscillator, connect a crystal or
tionally identical to RET. ceramic resonator between the XTALI and XTAL2 pins
of the microcontroller, and capacitors to ground as
Table 10 shows the list of conditional jumps available to shown in Figure 14.
the 8051 user. All of these jumps specify the destination
address by the relative offset method, and so are limited
to a jump distance of -128 to + 127 bytes from the in-
struction following the conditional jump instruction. Im-
portant to note, however, the user specifies to the as- HMOS
sembler the actual destination address the same way as OR CHWOS
the other jumps: as a label or a 16-bit constant. ,........--IXTA'2

OUAR~ ~~~~~~~~-==
RESONA.TOR
There is no Zero bit in the PSW. The JZ and JNZ in-
structions test the Accumulator data for that condition. ~""-l-lXT'"
vss
The DJNZ instruction (Decrement and Jump if Not Ze-
ro) is for loop control. To execute a loop N times, load
a counter byte with N and terminate the loop with a
DJNZ to the beginning of the loop, as shown below for N Fignre 14. Using the On-Chip Oscillator
~ 10:
Examples of how to drive the clock with an external os-
MOV COUNTER,#10 cillator are shown in Figure 15. Note that in the HMOS
LOOP: (begin loop) devices (8051, etc.) the signal at the XTAL2 pin actually
• drives the internal clock generator. In the CHMOS de-
• vices (80C51BH, etc.), the signal at the XTALI pin
• drives the internal clock generator. The internal clock
generator defines the sequence of states that make up
(end loop)
DJNZ COUNTER,LOOP the 8051 machine cycle.
(continue)
MACIDNE CYCLES
The CJNE instruction (Compare and Jump if Not Equal)
can also be used for loop control as in Figure 13. Two A machine cycle consists of a sequence of 6 states,
bytes are specified in the operand field of the instruc- numbered SI through S6. Each state time lasts for two
tion. The jump is executed only if the two bytes are not oscillator periods. Thus a machine cycle takes 12 oscil-
equal. In the example of Figure 13, the two bytes were lator periods or IJ.1S if the oscillator frequency is
data in R1 and the constant 2AH. The initial data in R1 12MHz.
was 2EH. Every time the loop was executed, R1 was
decremented, and the looping was to continue until the Each state is divided into a Phase 1 half and a Phase 2
Rl data reached 2AH. half. Figure 16 shows that fetch/execute sequences in
states and phases for various kinds of instructions. Nor-
Another application of this instruction is in "greater mally two program fetches are generated during each
than, less than" comparisons. The two bytes in the oper- machine cycle, even if the instruction being executed
and field are taken as unsigned integers. If the first is doesn't require it. If the instruction being executed
less than the second, then the Carry bit is set (1). If the doesn't need more code bytes, the CPU simply ignores
first is greater than or equal to the second, then the the extra fetch, and the Program Counter is not
Carry bit is cleared. incremented.
Table 10. Conditional Jumps in 8051 Devices

MnemoniC Operation
Dlr Ind Reg Imm Time (,...s)
JZ rei Jump if A = 0 Accumulator only 2
JNZ rei Jump if A*"O Accumulator only 2
DJNZ <byte> ,rei Decrement and jump if not zero X X 2
CJNE A, < byte> ,rei Jump if A *" <byte> X X 2
CJNE < byte> ,# data, rei Jump if <byte> *" #data X X 2
February 1989 1-15

Ports 0 and 2, and of ALE and PSEN. ALE is used to

HWOS latch the low address byte from PO into the address
OR eMMOS
latch.
XT4L.2
txTtRN4L
When the CPU is executing from internal Program
CLOCK XTAl.l Memory, PSEN is not activated, and program addresses
SIGHAL
vss are not emitted. However, ALE continues to he activated
twice per machine cycle and so it is available as a clock
output signal. Note, however, that one ALE is skipped
A. HMOS or CHMOS during the execution of the MOVX instruction.
HIrotOS
ontRMAL
ONLY INTERRUPT STRUCTURE
CLOCK
SIGN..L
The 8051, 8051AH, 80C5IBH, 83C451, and their
ROMless and EPROM versions, provide 5 interrupt
)O'4LI
sources: 2 external interrupts, 2 timer interrupts, and the
vss
serial port interrupt.
='"----
B. HMOS Only What follows is an overview of the interrupt structure for
these devices. More detailed information for specific
CHWO$
ONL'I' members of the 8051 family is provided in later chapters
(JoIC) XTALl of this handbook.
[XTER ... AL INTERRUPT ENABLES

CLOCK XTALI
SIQiAI.
vss
Each of the interrupt sources can be individually enabled
='"---- or disabled by setting or clearing a bit in the SFR
C. CHMOS Only named IE (Interrupt Enable). This register also contains
a global disable bit, which can be cleared to disable all
Figure 15. Using an External Clock
interrupts at once. Figure 18 shows the IE register for
the 8051 devices.
Execution of a one-cycle instruction (Figure 16A and B)
begins during State 1 of the machine cycle, when the INTERRUPT PRIORITIES
opcode is latched into the Instruction Register. A second
fetch occurs during S4 of the same machine cycle. Exe- Each interrupt source can also be individually pro-
cution is complete at the end of State 6 of this machine grammed to one of two priority levels by setting or
cycle. clearing a bit in the SFR named IP Interrupt Priority).
Figure 19 shows the IP register in the 8051.
The MOVX instructions take two machine cycles to exe-
cute. No program fetch is generated during the second A low-priority interrupt can be interrupted by a high-
cycle of a MOVX instruction. This is the only time pro- priority interrupt, but not by another low-priority inter-
gram fetches are skipped. The fetch/execute sequence rupt. A high-priority interrupt can't be interrupted by any
for MOVX instructions is shown in Figure 16D. other interrupt source.
The fetch/execute sequences are the same whether the If two interrupt requests of different priority levels are
Program Memory is internal or external to the chip. Ex- received simultaneously, the request of higher priority
ecution times do not depend on whether the Program level is serviced. If interrupt requests of the same prior-
Memory is internal or external. ity level are received simultaneously, an internal polling
sequence determines which request is serviced. Thus
Figure 17 shows the signals and timing involved in pro-
within each priority level there is a second priority struc-
gram fetches when the Program Memory is external. If
ture determined by the polling sequence.
Program Memory is external, then the Program Memory
read strobe PSEN is normally activated twice per ma-
Figure 20 shows, for the 8051, how the IE and IP regis-
chine cycle, as shown in Figure 17(A).
ters and the polling sequence work to determine which if
any interrupt will be serviced.
If an access to external Data Memory occurs, as shown
in Figure 17(B), two PSENs are skipped, because the
In operation, all the interrupt flags are latched into the
address and data bus are being used for the Data Mem- interrupt control system during State 5 of every machine
ory access.
cycle. The samples are polled during the following ma-
chine cycle. If the flag for an enabled interrupt is found
Note that a Data Memory bus cycle takes twice as much
to be set (1), the interrupt system generates an LCALL
time as a Program Memory bus cycle. Figure 17 shows
to the appropriate location in Program Memory, unless
the relative timing of the addresses being emitted at
some other condition blocks the interrupt. Several con-
February 1989 1-16

05C.
(XTAL2)
I 51 I 52 1 53 I
~~~~~~~~~~~~~~~~~~~~~~~~~~
54 I 55 1 III 1 51 I 52 I 53 I 54 I 55 1 56 1 51 I
ALE
_[ _R:~O NEXT OPCOOE AGAIN.
------~~--_r--~Lo--_r~
I
(All.byte, l-cycle I n l _ , •.g., INC A.
I
I READ OPCODE.
I
: _ f _ R : NEXT OPCODE.
- - - - - - - - r-''--T---'-:-:-T-:':-t-=:-r-::-1
(BI2-byIe, l-cycle Inlltuc:llon, •.g., ADD A, .da..
(C) 1.byte, 2..,,.,18 lnoluellan, •.g., INC DPTR.

I
I
READOPCODE
I (MOVX).
I
I
------~~--_r--~Lo--_r--~~~~--,_~r_~--~
DATA
(01 MOVX (l-by1e, 2-cyc1e)
I ACCESS EXTERNAL MEMORY
Figure 16. State Sequence in 8051 Family devices
ditions can block an interrupt, among them that an in- the stack, not the PSW or any other register. Having
terrupt of equal or higher priority level is already in only the PC be automatically saved allows the program-
progress. mer to decide how much time to spend saving which
other registers. This enhances the interrupt response
The hardware-generated LCAlL causes the contents of time, albeit at the expense of increasing the program-
the Program Counter to be pushed into the stack, and mer's burden of responsibility. As a result, many inter-
reloads the PC with the beginning address of the service rupt functions that are typical in control applications
routine. As previously noted (Figure 4), the service rou- toggling a port pin for example, or reloading a timer, or
tine for each interrupt begins at a fixed location. unloading a serial buffer can often be completed in less
time than it takes other architectures to complete.
Only the Program Counter is automatically pushed onto
February 1989 1-17

, O N E MACHINE CYCLE-r--0NE MACHINE CYCLEi
1~1~1"1~1"IUI~~~I"I~I"IUI
ALE
PsEN
(A)
AD --------+-----------~-----------+------------T_----------~:----- WITHOUT A
I
I MOVX.
P2 p~......-P..:.C-'H-O-U-T~X'-+_'PC..:....H:...;O:...;U-T--JX PCH OUT X'-~-PC-H-O-U-T~~
PO
, I I
I I
tPCLOUT tPCLOUT tpCLOUT t.PCLOUT

VAllO VALID VALID VALID
ALE
PSEN
liD --,---;-----~'---- (B)
WITH A
MOVX.
lADDIIOUT t.PCLOUT
VALID VALID
Figure 17. Bus Cycles iu 8051 Family Devices Executing from External Program Memory
SIMULATING A THIRD PRIORITY LEVEL As soon as any priority interrupt is acknowledged, the
IN SOFTWARE Interrupt Enable (IE) register is redefined so as to dis-
able all but "priority 2" interrupts. Then a CALL to LA-
Some applications require more than two priority levels BEL executes the RETI instruction, which clears the
that are provided by on-chip hardware in 8051 devices. priority 1 interrupt-in-progress flip-flop. At this point
In these cases, relatively simple software can be written any priority 1 interrupt that is enabled can be serviced,
to produce the same effect as a third priority level. First but only "priority 2" interrupts are enabled.
interrupts that are to have higher priority than 1 are as-
signed to priority 1 in the Interrupt Priority (IP) regis- POPing IE restores the original enable byte. Then a
ter. The service routines for priority 1 interrupts that normal RET (rather than another RETI) is used to ter-
are supposed to be interruptable by "priority 2" inter- minate the service routine. The additional software adds
rupts are written to include the following code: 1OJ.lS (at 12MHz) to priority 1 interrupts.
PUSH IE
MOV IE,#MASK
CALL LABEL
**********
(execute service routine)
**********
POP IE
RET
LABEL: RETI
February 1989 1-18

(MSB) (LSB)
I EA Ix I x IES IET1 IEXI IETO I EXO I (MSB) (LSB)
Symbol Poaltlon Function I x Ix I X IPS IPTI IPXl IPTO I pxo I

EA IE.7 disables all interrupts. If EA = 0, no
interrupt will be acknowledged. If EA = 1, Symbol P081110n Function
each interrupt source is individually IP.7 reserved
enabled or disabled by setting or claaring IP.6 reserved
"s enable bit. IP.5 reserved
1E.6 reserved. PS IP.4 defines the Serial Port interrupt priority

1E.5 reserved. level. PS '"' 1 programs it to the higher
priority level.
ES lEA enables or disables the Sarial Port
PTI IP.3 defines the Timer 1 interrupt priority
interrupt If ES = 0, the Serial Port
interrupt is disabled. level. PT1 - 1 programs it to the higher
priority level.
ETI IE.3 enables or disables the Timer 1 Overflow
interrupt. If ETI = 0, the Timer 1 interrupt PXl IP.2 defines the External Interrupt 1 priority
is disabled. level. PX1 '"' 1 programs it to the higher
priority level.
EXI IE.2 enables or disables External Interrupt 1. If
EXI = 0, External Interrupt 1 is disabled. PTO IP.l defines the Timer 0 interrupt priority
level. PTO '"' 1 programs It to the higher
ETO IE.l enables or disables the Timer 0 Overflow priority level.
interrupt. If ETO = 0, the Timer 0 interrupt
is disabled. PXO IP.O defines the External interrupt 0 priority
level. PXQ - 1 programs it to the higher
EXO IE.O enables or disables External Interrupt O. If priority level.
EXO = 0, Externallnterrupl 0 Is disabled.
Figure 18. Interrupt Enable (IE) Register Figure 19. Interrupt Priority (lP) Register
HIGH PRIORITY
IE REGISTER IP REGISTER INTERRUPT
~~--~~~--~~~~
I
I
I
TFO------.t--<:~ ~>-t-IO-~~~I-.I INTERRUPT

POLLING
SEQUENCE
I
I
I
. ./
TF1----------------~~~~(>-t---~r<~~-l-----J~
I
I
I
r----~~~~_t~~_4~
RI
TI
TF2
EXF2 (8052 ONLY)
INDIVIDUAL GLOBAL LOW PRIORITY

ENABLES DISABtE INTERRUPT
Figure 20. Interrupt Control System
February 1989 1-19

Section 1 8051 Family Hardware Description
HARDWARE DESCRIPTION • The port drivers and how they function both as ports
and, for Ports 0 and 2, in bus operations
This chapter provides a detailed description of the 8051 • The Timers/Counters
microcontrollers (see Figure 21). Included in this de- • The Serial Interface
scription are: • The Interrupt System
• Reset
• The Reduced Power Modes in CHMOS devices
• The EPROM version of the 80C51BH
r
I
::EI'
I
Li~-----------
February 1989 1-20

SPECIAL FUNCTION REGISTERS PROGRAM STATUS WORD
A Map of the on-chip memory area called Special Func- The PSW register contains program status information as
tion Register (SFR) space is shown in Figure 22. detailed in Figure 23.
Note that in the SFRs not all of the addresses are occu- STACK POINTER
pied. Unoccupied addresses are not implemented on the
chip. Read accesses to these addresses will in general The Stack Pointer register is 8 bits wide. It is incre-
return random data, and write accesses will have no ef- mented before data is stored during PUSH and CALL
fect. executions. While the stack may reside anywhere in on-
chip RAM, the Stack Pointer is initialized to 07H after
User software should not write Is to these unimple- a reset. This causes the stack to begin at locations 08H.
mented locations, since they may be used in other 8051
Family products to invoke new features. The function of DATA POINTER
the SFRs are described in the text that follows.
The Data Pointer (DPTR) consists of a high byte (DPH)
ACCUMULATOR and a low byte (DPL). Its intended function is to hold a
16-bit address. It may be manipulated as a 16-bit regis-
ACC is the Accumulator register. The mnemonics for ter or as two independent 8-bit registers.
Accumulator-Specific instructions, however, refer to the
Accumulator simply as A. PORTS 0 TO 3
B REGISTER PO, PI, P2 and P3 are the SFR latches of Ports 0, I, 2,

and 3 respectively.
The B register is used during multiply and divide opera-
tions. For other instructions it can be treated as another
scratch pad register.
8 BYTES
F'8 F'F'
F'O a F'7
E8 EF'
EO ACC E7
08 OF'
DO PSW 07
C8 CF'
CO C7
B8 IP BF'
BO P3 B7
A8 IE AF
AO P2 A7
98 SCON SBUF 9F
90 P1 97
B8 TCON TMOD TLO TL1 THO TH1 8F
eo PO SP DPL DPH PCON 87
-
alT
ADDRESSABLE
Figure 22. 80S1 SFR Memory Map
February 1989 1-21

(MSB) (LSB)
AC FO RSl RSO OV P
Symbol PoeIllon Name and Slgnlflcllnca Symbol Poeltlon Name and SlpnlflCance
CY PSW.7 Carry flag. OV PSW.2 Overflow Ilag.
AC PSW.S Auxiliary Carry flag. PSW.l User definable flag.
(For BCD operations.) P PSW.O Parilyflag.
FO PSW.S Flag 0 Set/cleared by hardware each
(Available to the user for general ins1ruction cycle to Indicate an oddl
purposes.) even number Of "one" bits in the
RSl PSW.4 Register bank select control bits 1 & Accumulator. i.e•• even parity.
RSO PSW.3 O. Set/cl_ed by software to NOTE:
determine working register benk (_ The contents Of (RS1. RSO) aneble the working register banks as
follows:
Note). (O.O)-Bank 0 (OOH-07H)
(O.l)-Bank 1 (OBH-OFH)
(1.0)-8ank 2 (10H-17H)
(l.l)-Bank 3 (18H-1FH)
Figure 23. Program Status Word (pSW) Register
SERIAL DATA BUFFER All the Port 3 pins are multifunctional. They are not only
port pins, but also serve the functions of various special
The Serial Buffer is actually two separate registers, a features as listed below:
transmit buffer and a receive buffer register. When data
is moved to SBUF, it goes to the transmit buffer is held Port
for serial transmission. (Moving a byte to SBUF is what Pin Alternate Function
initiates the transmission.) When data is moved from P3.0 RxD (serial input port)
SBUF, it comes from the receive buffer. P3.1 TxD (serial output port)
P3.2 INTO (external interrupt)
TIMER REGISTERS BASIC TO 8051 P3.3 INTI (external interrupt)
P3.4 TO (Timer/Counter 0 external input)
Register pairs (TIm, TID), and (ml, 11..1) are the P3.5 Tl (Timer/Counter 1 external input)
16-bit Counting registers for Timer/Counters 0, and 1 P3.6 WR (external Data Memory write strobe)
respectively. P3.7 RD (external Data Memory read strobe)
CONTROL REGISTERS FOR THE 8051 The alternate functions can only be activated if the cor-
responding bit latch in the port SFR contains a 1. Oth-
Special Function Registers IP, IE, TMOO, TCON, erwise the port pin remains at O.
SCON, and PCON contain control and status bits for the
interrupt system, the Timer/Counters, and the serial I/O CONFIGURATIONS
port. They are described in later sections.
Figure 24 shows a functional diagram ofa typical bit
PORT STRUCTURES AND latch and I/O buffer in each of the four ports. The bit
OPERATION latch (one bit in the port's SFR) is represented as a
Type D flip-flop, which will clock in a value from the in-
All four ports in the 8051 are bidirectional. Each con- ternal bus in response to a "write to latch" signal from
sists of a latch (Special Function Registers PO through the CPU. The Q output of the flip-flop is placed on the
P3), an output driver, and an input buffer. internal bus in response to a "read latch" signal from the
CPU. The level of the port pin itself is placed on the in-
The output drivers of Ports 0 and 2, and the input buffers ternal bus in response to a "read pin" signal from the
of Port 0, are used in accesses to external memory. In CPU. Some instructions that read a port activate the
this application, Port 0 outputs the low byte of the exter- "read latch" signal, and others activate the "read pin"
nal memory address, time-multiplexed with the byte signal.
being written or read.
As shown in Figure 24, the output drivers of Port 0 and
Port 2 outputs the high byte of the external memory ad- 2 are switchable to an internal ADDR and ADDRI DA-
dress when the address is 16 bits wide. Otherwise, the TA bus by an internal CONTROL signal for use in exter-
Port 2 pins continue to emit the P2 SFR content.
February 1989 1-22

REAO
Vcc LATCH
WRITE
TO
WRITE LATCH
TO
LATCH
READ
PIN
B. Port·1 Bit
A. PortO Bit ALTERNATE
OUTPUT
FUNCTION
AOOR
VCC READ
READ LATCH
LATCH
tNT. BUS
INT. BUS WRITE

TO
WRITE LATCH
TO
LATCH
ALTERNATE
INPUT
FUNCTION
c. Port 2 Bit D. Port 3 B,t
Figure 24. 8051 Port Bit Latches and 110 Buffers

*See Figure 25 for details of the internal pullup.
nal memory accesses. During external memory accesses, FET in the PO output driver (see Figure 24) is used only
the P2 SFR remains unchanged, but the PO SFR gets 1s when the port is emitting 1s during external memory ac-
written to it. cesses. Otherwise the pullup FET is off. Consequently PO
lines that are being used as output port lines are open
Also shown in Figure 24, is that if a P3 bit latch con- drain. Writing a 1 to the bit latch leaves both output
tains a 1, then the output level is controlled by the signal FETs off, so the pin floats. In that condition it can be
labeled "alternate output function". The actual P3.X pin used a high-impedance input.
level is always available to the pin's alternate input func-
tion, if any. Because Ports 1, 2, and 3 have fixed internal pullups
they are sometimes called "quasi-bidirectional" ports.
Ports 1, 2, and 3 have internal pullups. Port 0 has open When configured as inputs they pull high and will source
drain outputs. Each I/O line can be independently used current (hL, in the data sheets) when externally pulled
as an input or an output. (Port 0 and 2 may not be used low. Port 0, on the other hand, is considered "true"
as general purpose I/O when being used as the ADDRI bidirectional, because when configured as an input it
DATA BUS). To be used as an input, the port bit latch floats.
must contain a 1, which turns off the output driver FET.
Then, for Ports 1, 2, and 3, the pin is pulled high by the All the port latches in the 8051 have 1s written to them
internal pullup, but can be pulled low by an external by the reset function. If a 0 is subsequently written to a
source. port latch, it can be reconfigured as an input by writing
a 1 to it.
Port 0 differs in not having internal pullups. The pullup
February 1989 1-23

VCC
ENHANCEMENT MODE FET
6D......... . . - - - - - - - -
A. HMOS Configuration. The enhancement mode transistor

Is turned on for 2 08C. perlod8 after Q make8 a 1-to-O tran8ltlon.
a
FROM PORT
LATCH
INPUT CI---C I-~-<

DATA
READ
PORT PIN
B. CHMOS Configuration. pFET 1 18 turned on for 2 08C. periods after Q

makes a 1-to-0 tran8ltlon. During this time, pFET 1 also turns on pFET 3
through the Inverter to form a latch which holds the 1. pFET 21s also on.
Figure 25. Ports 1 and 3 HMOS and CHMOS Internal Pullup Configurations
Port 2 is similar except that it holds the strong pullup on while emitting
is that are address bits. (See Accessing External Memory).
WRITING TO A PORT are field-effect transistors, not linear resistors. The

pullup arrangements are shown in Figure 25.
In the execution of an instruction that changes the value
in a port latch, the new value arrives at the latch during In HMOS versions of the 8051, the fixed part of the
S6P2 of the final cycle of the instruction. However, port pullup is a depletion mode transistor with the gate wired
latches are in fact sampled by their outpnt buffers only to the source. This transistor will allow the pin to source
during Phase 1 of any clock period. (During Phase 2 the about 0.25mA when shorted to ground. In parallel with
output buffer holds the value it saw during the previous the fixed pullup is an enhancement mode transistor,
Phase 1). Consequently, the new value in the port latch which is activated during Sl whenever the port bit does
won't actually appear at the output pin until the next a 0-to-1 transition. During this interval, if the port pin
Phase 1, which will be at SlP1 of the next machine cy- is shorted to ground, this extra transistor will allow the
cle. pin to source an additional 30mA.
If the change requires a 0-to-1 transition in Port 1, 2, In the CHMOS versions, the pullup consists of three
or 3, an additional pullup is turned on during SlP1 and pFETs. It should be noted that an n-channel FET
SlP2 of the cycle in which the transition occurs. This is (nFET) is turned on when a logical 1 is applied to its
done to increase the transition speed. The extra pullup gate, and is turned off when a logical 0 is applied to its
can source about 100 times the current that the normal gate. A p-channel FET (PFET is the opposite: it is on
pullup can. It should be noted that the internal pullups when its gate sees a 0, and off when its gate sees a 1.
February 1989 1-24

Si 9 netics M icroprocesso r Prod ucts User's Guide
pFET1 in Figure 25 is the transistor that is turned on It is not obvious that the last three instructions in this
for 2 oscillator periods after a 0-to-1 transition in the list are read-modifY-write instructions, but they are.
port latch. While it's on, it turns on pFET3 (a weak They read the port byte, all 8 bits, modify the addressed
pullup), through the inverter. TIlis inverter and pPET bit, then write the new byte back to the latch.
form a latch which hold the 1.
The reason that read-modifY-write instructions are di-
Note that if the pin is emitting a 1, a negative glitch on rected to the latch rather than the pin is to avoid a pos-
the pin from some external source can turn off pFET3, sible misinterpretation of the voltage level at the pin.
causing the pin to go into a float state. pFET is a very For example, a port bit might be used to drive the base
weak pullup which is on whenever the nFET is off, in of a transistor. Vllhen a 1 is written to the bit, the tran-
traditional CMOS style. It's only about 1/10 the strength sistor is turned on. If the CPU then reads the same port
of pFET3. Its function is to restore a 1 to the pin in the bit at the pin rather than the latch, it will read the base
event the pin had a 1 and lost it to a glitch. voltage of the transistor and interpret it as a O. Reading
the latch rather than the pin will return the correct val-
PORT LOADING AND INTERFACING ue of 1.
TIle output buffers of Ports 1, 2, and 3 can each drive 4 ACCESSING EXTERNAL
LS 1TL inputs. These ports on HMOS versions can be MEMORY
driven in a normal malller by any TTL or NMOS cir-
cuit. Both HMOS and CHMOS pins can be driven by Accesses to external memory are of two types: accesses
open-collector and open-drain outputs, but note that 0- to external Program Memory and accesses to external
to-1 transitions will not be fast. Data Memory. Accesses to external Program Memory
use signal PSEN (program store enable) as the read
In the HMOS device, if the pin is driven by an open- strobe. Accesses to external Data Memory use RD or
collector output, a 0-to-1 transition will have to be driv- WR (alternate functions of P3.7 and P3.6) to strobe the
en by the relatively weak depletion mode FET in Figure memory. Fetches from external Program Memory always
25(A). In the CHMOS device, an input 0 turns off use a 16-bit address. Accesses to external Data Memory
pullup pFET3, leaving only the very weak pullup pFET2 can use either a 16-bit address (MOVX @ DPTR) or an
to drive the transition. 8-bit address (MOVX @Ri).
Port 0 output buffers can each drive 8 LS TTL inputs. Whenever a 16-bit address is used, the high byte of the
TI,ey do, however, require external pullups to drive address comes out on Port 2, where it is held for the
NMOS inputs, except when being used as the AD- duration of the read or write cycle. Note that the Port 2
DRESS/DATA bus.
drivers use the strong pull ups during the entire time that
they are emitting address bits that are 1s. This is during
READ-MODIFY-WRITE FEATURE
the execution of a MOVX @DPTR instruction. During
Some instructions that read a port read the latch and this time the Port 2 latch (the Special Function Regis-
others read the pin. Which ones do which? The instruc- ter) does not have to contain 1s, and the contents of the
tions that read the latch rather than the pin are the ones Port 2 SFR are not modified. If the external memory
cycle is not immediately followed by another external
that read a value, possibly change it, and then rewrite it
to the latch. These are called "read-modify-write" in- memory cycle, the undisturbed contents of the Port 2
structions. The instructions listed below are read-modify- SFR will reappear in the next cycle.
'Write instructions. \\Thon the destination operand is a
If an 8-bit address is being used (MOVX @Ri), the con-
port, or a port bit, these instructions read the latch
tents of the Port 2 SFR remain at the Port 2 pins
rather than the pin:
throughout the external memory cycle. This will facili-
ANL tate paging.
(logical AND, e.g. ANL P1,A)
ORL (logical OR, e.g. ORL P2,A)
In any case, the low byte of the address is time-
XRL (logical EX-OR, e.g. XRL
multiplexed with the data byte on Port O. The ADDRI
P3,A)
JBC DATA signals drives both FETs in the Port 0 output
(jump if bit = 1 and clear
buffers. Thus, in this application the Port 0 pins are not
bit, e.g. JBC P1.1,LABEL)
open-drain outputs, and do not require external pull ups.
CPL (complement bit, e.g.
ALE (Address Latch Enable) should be used to capture
CPL P3.0)
the address byte into an external latch. The address byte
INC (increment, e.g. INC P2)
is valid at the negative transition of ALE. Then, in a
DEC (decrement, e.g. DEC P2)
write cycle, the data byte to be written appears on Port
DJNZ (decrement and jump if not
zero, e.g. DJNZ P3,LABEL)
o just before WR is activated, and remains there until
after WR is deactivated. In a read cycle, the incoming
MOV,PX.Y,C (move carry bit to bit Y of
byte is accepted at Port 0 just before the read strobe is
Port X)
deactivated.
CLR PX.Y (clear bit Y of Port X)
SET PX.Y (set bit Y of Port X)
February 1989 1-25

During any access to external memory, the CPU writes In the "Counter" function, the register is incremented in
OFFH to the Port 0 latch (the Special Function Regis- response to a I-to-O transition at its corresponding ex-
ter), thus obliterating whatever information the Port 0 ternal input pin, TO or Tl. In this function, the external
SFR may have been holding. input is sampled during SSP2 of every machine cycle.
External Program Memory is accessed under two condi- When the samples show a high in one cycle and a low in
tions: Whenever signal EA is active; or whenever the the next cycle, the count is incremented. The new count
program counter (PC) contains a number that is larger value appears in the register during S3Pl of the cycle
than OFFFH (in the 8051). following the one in which the transition was detected.
Since it takes 2 machine cycles (24 oscillator periods)
This requires that the ROMless versions have EA wired to recognize a I-to-O transition, the maximum count rate
low to enable the lower 4K program bytes to be fetched is 1124 of the oscillator frequency. There are no restric-
from external memory. tions on the duty cycle of the external input signal, but
to ensure that a given level is sampled at least once be-
When the CPU is executing out of external Program fore it changes, it should be held for at least one full
Memory, all 8 bits of Port 2 are dedicated to an output cycle. In addition to the "Timer" or "Counter" selection,
function and may not be used for general purpose I/O. Timer 0 and Timer 1 have four operating modes from
During external program fetches they output the high which to select.
byte of the Pc. During this time the Port 2 drivers use
the strong pullups to emit PC bits that are Is. TIMER 0 AND TIMER 1
TIMER/COUNTERS The "Timer" or "Counter" function is selected by control

bits CIT in the Special Function Register TMOD. These
The 8051 has two 16-bit Timer/Counter registers: Timer two Timer/Counters have four operating modes, which
o and Timer 1. Both can be configured to operate either are selected by bit-pairs (Ml, MO) in TMOD. Modes 0,
as timers or event counters (see Figure 26). 1, and 2 are the same for both Timers/Counters. Mode 3
is different. The four operating modes are described in
In the "Timer" function, the register is incremented eve- the following text.
ry machine cycle. Thus, one can think of it as counting
machine cycles. Since a machine cycle consists of 12
oscillator periods, the count rate is 1112 of the oscillator
frequency.
(MSB)
l GATE CIT Ml MO 1 GATE CIT J Ml
(lSB)
MO J
Timer 1
•
Timer 0
GATE Gating control when set. Timer/Counter "x" is enabled Ml MO Operating Mode
only while "INTx" pin is high and "TAx" control pin is o o 8048 Timer "TLx" se,:,ves as 5--blt prescaler.
set. When cleared Timer 'Ix" is enabled whenever o 16-bit Timer/Counter "THx" and "Tlx" are
"TAx" control bit is set.
cascaded; there is no prescaler.
CIT Timer or Counter Selector cleared for Timer operation
(input from internal system clock). Set for Counter
o 8-bit auto-reload Timer/Counter "THx" holds a
value which is to be reloaded into "Tlx" each
operation (input from "Tx" input pin).
time it overflows.
(Timer 0) TlO is an 8-bit TImer/Counter
controlled by the standard TImer 0 control bits.
THO is an 8-bit timer only controlled by Timer 1
control bits.
(Timer 1) Timer/Counter 1 stopped.
Figure 26_ Tlmer/Connter Mode Control (TMOD) Register
February 1989 1-26

MODE 0 Mode 2 operation is the same for Timer/Counter O.
Putting either Timer into Mode 0 makes it look like an MODE 3

8048 Timer, which is an 8-bit Counter with a divide-by-
32 prescaler. Figure 27 shows the Mode 0 operation as Timer 1 in Mode 3 simply holds its count. The effect is
it applies to Timer 1. the same as setting IR1 = O.
In this mode, the Timer register is configured as a 13- Timer 0 in Mode 3 establishes 1LO and 11f0 as two
bit register. As the count rolls over from all Is to all separate counters. The logic for Mode 3 on Timer 0 is
Os, it sets the Timer interrupt flag TF1. The counted in- shown in Figure 30. 1LO uses the Timer 0 control bits:
put is enabled to the Timer when IR1 = 1 and either CIT, GATE, IRO, INTO, and TFO. 11f0 is locked into a
GATE = 0 or INfl = 1. (Setting GATE = 1 allows the timer function (counting machine cycles) and takes over
Timer to be controlled by external input INf1, to facili- the use of IR1 and TF1 from Timer 1. Thus, 11f0 now
tate pulse width measurements). IR1 is a control bit in controls the "Timer 1" interrupt.
the Special Function Register TCON (Figure 28).
GATE is in TMOD. Mode 3 is provided for applications reqUlrmg an extra
8-bit timer on the counte~. With Timer 0 in Mode 3, an
The 13-Bit register consists of all 8 bits of 11f1 and the 8051 can look like it has three Timer/Counters. When
lower 5 bits of 1L1. The upper 3 bits of 1L1 are inde- Timer 0 is in Mode 3, Timer 1 can be turned on and off
terminate and should be ignored. Setting the run flag by switching it out of and into its own Mode 3, or can
(IR1) does not clear the registers. still be used by the serial port as a baud rate generator,
or in fact, in any application not requiring an interrupt.
Mode 0 operation is the same for the Timer 0 as for
Timer 1. Substitute IRO, TFO and INfO for the corre- STANDARD SERIAL INTERFACE
sponding Timer 1 signals in Figure 27. There are two
different GATE bits, one for Timer 1 (TMOD.7) and The serial port is full duplex, meaning it can transmit
one for Timer 0 (TMOD.3). and receive simultaneously. It is also receive-buffered,
meaning it can commence reception of a second byte
MODE 1 before a previously received byte has been read from the
register. (However, if the first byte still hasn't been read
Mode 1 is the same as Mode 0, except that the Timer by the time reception of the second byte is complete,
register is being run with all 16 bits. one of the bytes will be lost). The serial port receive
and transmit registers are both accessed at Special
MODE 2 Function Register SBUF. Writing to SBUF loads the
transmit register, and reading SBUF accesses a physi-
Mode 2 configures the Timer register as an 8-bit cally separate receive register.
Counter (1L1) with automatic reload, as shown in Fig-
ure 29. Overflow from 1L1 not only sets TF1, but also The serial port can operate in 4 modes:
reloads 1L1 with the contents of 11f1, which is preset by
software. The reload leaves 11f1 unchanged.
CIT. 0
INTERRUPT
T1 PIN
______-'1 elf·
-
1
Figure 27. Timer/Counter 1 Mode 0: 13-Bit Counter
February 1989 1-27

Si gnetics Microprocessor Products User's Guide
(MSB) (LSB)
TFI TAl TFO TFjO lEI ITI lEO ITO
Symbol Poallton Name and SignifICance Symbol PoaIlion Name and Slgnlllcance
TFI TCON.7 Timer I overflow Flag. Set by lEI TCON.3 Interrupt I Edge flag. Set by hardware
hardware on Timer/Counter overflow. when external Interrupt edge
Cleared by hardware when processor detected. Cleansd when Interrupt
vectors to interrupt routine. processed.
TRI TCON.6 Timer I Run control bit. Set/cleared In TCON.2 Interrupt I Type control bH. Set!
by software to turn Timer/Counter on/ cleared by software to specify failing
011. edge/low level triggensd external
Interrupts.
TFO TCON.5 Timer 0 overflow Flag. Set by
hardware on Timer/Counter overflow. lEO TCON.I Interrupt 0 Edga flag. Set by hardware
Cleared by hardware when processor when external interrupt edge
vectors to interrupt routine. detected. Cleared when interrupt
processed.
TRO TCON.4 Timer 0 Run control bH. Set/cleared
by software to turn Timer/Counter on/ ITO TCON.O Interrupt 0 Type control bit. Set/
011. cleared by software to specify falling
edge/low level triggered external
Interrupts.
Figure 28. Timer/Counter Control (TCON) Register
INTERRUPT
Figure 29. Timer/Counter 1 Mode 2: 8-Bit Auto-Load
February 1989 1-28

B--B-
1112 lose -------,
1' 1210SC
INTERRUPT
TO PIN------~
CONTROL
GATE
1'1210SC-----------1~f-! .~INTERRUPT
TR1 ____________ ~TROL
~
Figure 30. Timer/Counter 0 Mode 3: Two 8-Bit Counters
Mode 0: Serial data enters and exits through RxD. MULTIPROCESSOR COMMUNICATIONS
TxD outputs the shift clock. 8 bits are transmitted/re-
ceived (LSB first). The baud is fixed at 1112 the oscilla- Modes 2 and 3 have a special provision for multiproces-
tor frequency. sor communications. In these modes, 9 data bits are re-
ceived. The 9th one goes into RB8. Then comes a stop
Mode 1: 10 bits are transmitted (through TxD) or re- bit. The port can be programmed such that when the
ceived (through Rx D): a start bit (0), 8 data bits (LSB stop bit is received, the serial port interrupt will be ac-
first), and a stop bit (1). On receive, the stop bit goes tivated only if REB = 1. This feature is enabled by set-
into RB8 in Special Function Register SCaN. The baud ting bit SM2 in SCaN. A way to use this feature in
rate is variable. multiprocessor systems is as follows:
Mode 2: 11 bits are transmitted (through TxD) or re- When the master processor wants to transmit a block of
ceived (through RxD): start bit (0), 8 data bits (LSB data to one of several slaves, it first sends out an ad-
first), a programmable 9th data bit, and a stop bit (1). dress byte which identifies the target slave. An address
On Transmit, the 9th data bit (TB8 in SCaN) can be byte differs from a data byte in that the 9th bit is 1 in
assigned the value of 0 or 1. Or, for example, the parity an address byte and 0 in a data byte. With SM2 = 1, no
bit (P, in the PSW) could be moved into TB8. On re- slave will be interrupted by a data byte. An address byte,
ceive, the 9th data bit goes into RB8 in Special Func- however, will interrupt all slaves, so that each slave can
tion Register SCaN, while the stop bit is ignored. The examine the received byte and see if it is being ad-
baud rate is programmable to either 1/32 or 1/62 the dressed. The addressed slave will clear its SM2 bit and
oscillator frequency. prepare to receive the data bytes that will be coming.
The slaves that weren't being addressed leave their
Mode 3: 11 bits are transmitted (through TxD) or re- SM2s set and go on about their business, ignoring the
ceived (through RxD): a start bit (0), 8 data bits (LSB coming data bytes.
first), a programmable 9th data bit and a stop bit (1).
In fact, Mode 3 is the same as Mode 2 in all respects SM2 has no effect in Mode 0, and in Mode 1 can be
except baud rate. The baud ·rate in Mode 3 is variable. used to check the validity of the stop bit. In a Mode 1
reception, if SM2 = 1, the receive interrupt will not be
In all four modes, transmission is initiated by any in- activated unless a valid stop bit is received.
struction that uses SBUF as a destination register. Re-
ception is initiated in Mode 0 by the condition RI = 0 SERIAL PORT CONTROL REGISTER
and REN = 1. Reception is initiated in the other modes
by the incoming start bit if REN = 1. The serial port control and statu~ register is the Special
Function Register SCaN, shown in Figure 31. This reg-
ister contains not only the mode selection bits, but also
the 9th data bit for transmit and receive (TBB and RBS),
and the serial port interrupt bits (Tl and Rl).
February 1989 1-29

(MSB) (LSB)
SMO SM' SM2 AEN TB8 AB8 TI AI
Where SMO, SM' specify the serial port mode, as follows: • TB8 is the 9th data bit that will be
transmitted in Modes 2 and 3. Set or
SMO
0
0
SMI
0
1
0
Mode
0
1
2
Description
shift register
II-bitUART
9-bitUAAT
Baud Rat.
losc/ 12
variable
lose/54
. RBe
clear by software as desired.
in Modes 2 and 3, is the 9th data bit
that was received. In Mode I, if SM2
= 0, AB8 is the stop bij that was
.
or
fosc/32 received. In Mode 0, RB8 is not used.
3 9-bit UAAT variable TI is transm~ interrupt flag. Set by
• SM2 enables the multiprocessor hardware at the end of the 8th M time
communication feature in Modes in Mode 0, or at the beginning of the
2 and 3. In Mode 2 or 3, if SM2 is stop bit in the other modes, in any
set to 1 then RI will not be serial transmission. Must be cleared
activated if the received 9th data by software.
M (AB8) is O. In Mode I, if SM2
= 1 then RI will not be activated • AI is receive interrupt flag. Set by
if a valid stop bit was not hardware at the end of the 8th bit time
received. In Mode 0, SM2 should in Mode 0, or halfway through tha stop
beO. bit time in the other modes, in any
• REN enables serial reception. Set by serial reception (except see SM2).
software to enable reception. Must be cleared by software.
Clear by software to disable
reception.
Figure 31- Serial Port Control (SCON) Register
BAUD RATES The Timer 1 interrupt should be disabled in this applica-

tion. The Timer itself can be configured for either "tim-
The baud rate in Mode 0 is fixed: Mode 0 Baud Rate = er" or "counter" operation, and in any of its 3 running
Oscillator Frequency / 12. The baud rate in Mode 2 de- modes. In the most typical applications, it is configured
pends on the value of bit SMOD in Special Function for "timer" operation, in the auto-reload mode (high
Register peON. If SMOD = 0 (which is the value on re- nibble of TMOD = 001OB). In that case the baud rate is
set), the baud rate is 1164 the oscillator frequency. If given by the formula:
SMOD = 1, the baud rate is 1132 the oscillator fre-
quency. Mode 1, 3 Baud Rate =
Mode 2 Baud Rate = 2SMOD Oscillator Frequency

-3-2- x 12 X [256 - (TIll)]
2 SMOD
~ x (Oscillator Frequency) One can achieve very low baud rates with Timer 1 by
leaving the Timer 1 interrupt enabled, and configuring
In the 8051, the baud rates in Modes 1 and 3 are de- the Timer to run as a 16-bit timer (high nibble of
termined by the Timer 1 overflow rate. TMOD = 0001B), and using the Timer 1 interrupt to do
a 16-bit software reload. Figure 32 lists various com-
USING TIMER 1 TO GENERATE BAUD RATES monly used baud rates and how they can be obtained
from Timer 1.
When Timer 1 is used as the baud rate generator, the
baud rates in Modes 1 and 3 are determined by the MORE ABOUT MODE 0
Timer 1 overflow rate and the value of SMOD as fol-
lows: Serial data enters and exists through RxD. TxD outputs
the shift clock. 8 bits are transmitted/received: 8 data
Mode 1, 3 Baud Rate = bits (LSB first). The baud rate is fixed at 1112 the oscil-
lator frequency.
2SMOD
----n-- x (Timer 1 Overflow Rate) Figure 33 shows a simplified functional diagram of the
serial port in Mode 0, and associated timing.
February 1989 1-30

Timer 1
Baud Rate fose SMOD
CIT Mode Reload
Value
Mode 0 Max: 1 MHZ 12 MHZ X X X X
Mode 2 Max: 375K 12MHZ 1 X X X
Modes 1, 3: 62.5K 12MHZ 1 0 2 FFH
19.2K 11.059 MHZ 1 0 2 FDH
9.6K 11.059 MHZ 0 0 2 FDH
4.8K 11.059 MHZ 0 0 2 FAH
2.4K 11.059 MHZ 0 0 2 F4H
1.2K 11.059 MHZ 0 0 2 E8H
137.5 11.986 MHZ 0 0 2 1DH-
110 6MHZ 0 0 2 72H
110 12MHZ 0 0 1 FEEBH
Figure 32. Timer 1 Generated Commonly Used Baud Rates
Transmission is initiated by any instruction that uses the right is the value that was sampled at the P3.0 pin
SBUF as a destination register. The "write to SBUF" at S5P2 of the same machine cycle.
signal at S6P2 also loads a 1 into the 9th position of the
transmit shift register and tells the TX Control block to As data bits come in from the right, Is shift out to the
commence a transmission. The internal timing is such left. When the 0 that was initially loaded into the right-
that one full machine cycle will elapse between "write to most position arrives at the leftmost position in the shift
SBUF", and activation of SEND. register, it flags the RX Control block to do one last
shift and load SBUF. At SlP1 of the 10th machine cycle
SEND enables the output of the shift register to the al- after the write to SCaN that cleared RI, RECEIVE is
ternate output function line of P3.0 and also enables cleared as RI is set.
SHIFT CLOCK to the alternate output function line of
P3.I. SHIFT CLOCK is low during S3, S4, and S5 of MORE ABOUT MODE 1
every machine cycle, and high during S6, Sl and S2. At
S6P2 of every machine cycle in which SEND is active, Ten bits are transmitted (through TxD), or received
the contents of the transmit shift are shifted to the right (through RxD): a start bit (0), 8 data bits (LSB first),
one position. and a stop bit (1). On receive, the stop bit goes into
RE8 in SCaN. In the 8051 the baud rate is determined
As data bits shift out to the right, zeros come in from by the Timer 1 overflow rate.
the left. When the MSB of the data byte is at the output
position of the shift register, then the 1 that was initially Figure 34 shows a simplified functional diagram of the
loaded into the 9th position, is just to the left of the serial port in Mode 1, and associated timings for trans-
MSB, and all positions to the left of that contain zeros. mit receive.
This condition flags the TX Control block to do one last
shift and then deactivate SEND and set TL Both of Transmission is initiated by any instruction that uses
these actions occur at SlP1 of the 10th machine cycle SBUF as a destination register. The "write to SBUF"
after "write to SBUF". signal also loads a 1 into the 9th bit position of the
transmit shift register and flags the TX Control unit that
Reception is initiated by the condition REN = 1 and R1 a transmission is requested. Transmission actually com-
= O. At S6P2 of the next machine cycle, the RX Control mences at S1P1 of the machine cycle following the next
unit writes the bits 11111110 to the receive shift regis- rollover in the divide-by-16 counter. (Thus, the bit times
ter, and in the next clock phase activates RECEIVE. are synchronized to the divide-by-16 counter, not to the
"write to SBUF" signal).
RECEIVE enables SHIFT CLOCK to the alternate out-
put function line of P3.L SHIFT CLOCK makes transi- The transmission begins with activation of SEND which
tions at S3P1 and S6P1 of every machine cycle. At puts the start bit at TxD. One bit time later, DATA is
S6P2 of every machine cycle in which RECEIVE is ac- activated, which enables the output bit of the transmit
tive, the contents of the receive shift register are shifted shift register to TxD. The first shift pulse occurs one bit
to the left one position. The value that comes in from time after that.
February 1989 1-31

WRITE
TO
SBUF ---li-:~t;i:j=~--jJ~--~~------~r-'\ Rxe
P3.0ALT
OUTPUT
FUNCTION
sa --..-------~
Txe
P3.1 ALT
OUTPUT
FUNCTION
' - - - - - . I RX CLOCK
RX CONTROL SHIFT
REON
I----~ START
Ai Rxe
r.L-IU-...L..L-IU-I-..1____ P3.0 ALT
INPUT
FUNCTION
REAO
SBUF
ALE
---JtWRITE TO saUF
SEND S8P2 I
SHIFT
RXD (DATA OUT) \ TRANSMIT

TXD (SHIFT CLOCK)
TI
-.l1 WRITE TO SCON (CLEAR RI)
~AII~~====Jr====================================================~r----
~CEIVE
SHIFT
L--
RECEIVE
RXD (DATA IN)-~-[J!!l!:::--Ql=!.!....--{}~---{}!!!--~L--{)!i!!""--oe!.---{}2!~
TXD (SHIFT CLOCK)
Figure 33. Serial Port Mode 0
February 1989 1-32

TIMER1
OVERFLOW
WRITE
SBUF
TO --~r--:==:{~~~--~~:----'----~~ ~r-... __ TXD
As data bits shift out to the right, zeros are clocked iu Reception is initiated by a detected I-to-O transition at
from the left. When the MSB of the data byte is at the RxD. For this purpose RxD is sampled at a rate of 16
output position of the shift register, then the 1 that was times whatever baud rate has been established. When a
initially loaded into the 9th position is just to the left of transition is detected, the divide-by-16 counter is imme-
the MSB, and all positions to the left of that contain ze- diately reset, and IFFH is written into the input shift
ros. This condition flags the TX Control unit to do one register. Resetting the divide·by-16 counter aligns its
last shift and then deactivate SEND and set TI. This rollovers with the boundaries of the incoming bit times.
occurs at the 10th divide-by-16 rollover after "write to
SBUF".
February 1989 1-33

The 16 states of the counter divide each bit time into into the 9th bit position of the shift register. Thereafter,
16ths. At the 7th, 8th, and 9th counter states of each bit only zeros are clocked in. Thus, as data bits shift out to
time, the bit detector samples the value of RxD. The the right, zeros are clocked in from the left. When TB8
value accepted is the value that was seen in at least 2 of is at the output position of the shift register, then the
the 3 samples. This is done for noise rejection. If the stop bit is just to the left of TB8, and all positions to the
value accepted during the first bit time is not 0, the re- left of that contain zeros. This condition flags the TX
ceive circuits are reset and the uD.itgoes back to looking Control unit to do one last shift and then deactivate
for another 1-to-O transition. This is to provide rejection SEND and set TI. This occurs at the 11th divide-by-16
of false start bits. If the start bit proves valid, it is shift- rollover after "write to SUBF".
ed into the input shift register, and reception of the rest
of the frame will proceed. Reception is initiated by a detected 1-to-0 transition at
RxD. For this purpose RxD is sampled at a rate of 16
As data bits come in from the right, 1s shift out to the times whatever baud rate has been established. When a
left. When the start bit arrives at the leftmost position in transition is detected, the divide-by-16 counter is imme-
the shift register, (which in mode 1 is a 9-bit register), diately reset, and 1FFH is written to the input shift reg-
it flags the RX Control block to do one last shift, load ister.
SBUF and RB8, and set RI. The signal to load SBUF
and RB8, and to set RI, will generated if, and only if, At the 7th, 8th and 9th counter states of each bit time,
the following conditions are met at the time the final the bit detector samples the value of R-D. The value ac-
shift pulse is generated. cepted is the value that was seen in at least 2 of the 3
samples. If the value accepted during the first bit time is
1. R1 = 0, and not 0, the receive circuits are reset and the unit goes
2. Either SM2 = 0, or the received stop bit = 1 back to looking for another 1-to-O transition. If the start
bit proves valid, it is shifted into the input shift register,
If either of these two conditions is not met, the received and reception of the rest of the frame will proceed.
frame is irretrievably lost. If both conditions are met,
the stop bit goes into RB8, the 8 data bits go into SBUF, As data bits come in from the right, 1s shift out to the
and RI is activated. At this time, whether the above con- left. When the start bit arrives at the leftmost position in
ditions are met or not, the unit goes back to looking for the shift register (which in Modes 2 and 3 is a 9-bit reg-
a 1-to-0 transition in RxD. ister), it flags the RX Control block to do one last shift,
load SBUF and RB8, and set RI.
MORE ABOUT MODES 2 AND 3
The signal to load SBUF and RB8, and to set RI, will be
Eleven bits are transmitted (through TxD), or received generated if, and only if, the following conditions are
(through RxD): a start bit (0), 8 data bits (LSB first), a met at the time the final shift pulse is generated.
programmable 9th data bit, and a stop bit (1). On
transmit, the 9th data bit (TB8) can be assigned the val- 1. RI = 0, and
ue of ° or 1. On receive, the 9th data bit goes into RB8
in SCON. The baud rate is programmable to either 1132
2. Either SM2 = ° or the received 9th data bit =
or 1/64 the oscillator frequency in Mode 2. Mode 3 may If either of these conditions is not met, the received
have a variable baud rate generated from Timer 1. frame is irretrievably lost, and RI is not set. If both
conditions are met, the received 9th data bit goes into
Figures 35 and 36 show a functional diagram of the se- RB8, and the first 8 data bits go into SBUF. One bit
rial port in Modes 2 and 3. The receive portion is ex- time later, whether the above conditions were met or
actly the same as in Mode 1. The transmit portion dif- not, the unit goes back to looking for a 1-to-O transition
fers from Mode 1 only in the 9th bit of the transmit shift at the RxD input.
register.
INTERRUPTS
Transmission is initiated by any instruction that uses
SBUF as a destination register. The "write to SBUF" The 8051 provides 5 interrupt sources. These are shown
signal also loads TB8 into the 9th bit position of the in Figure 37. The External Interrupts INTO and INT1
transmit shift register and flags the TX Control unit that can each be either level-activated or transition-activated,
a transmission is requested. Transmission commences depending on bits ITO and ITl in Register TCON. The
at SlP1 of the machine cycle following the next roll-over flags that actually generate. these interrupts are bits lEO
in the divide-by-16 counter (thus, the bit times are syn- and IE1 in TCON. When an external interrupt is gener-
chronized to the divide-by-16 counter, not to the "write ated, the flag that generated it is cleared by the hard-
toSBUF" signal). ware when the service routine is vectored to only if the
interrupt was transition-activated. If the interrupt was
The transmission begins with activation of SEND, which level activated, then the external requesting source is
puts the start bit at TxD. One bit time later, DATA is what controls the request flag, rather than the on-chip
activated, which enables the output bit of the transmit hardware.
shift register to TxD. The first shift pulse occurs one bit
time after that. The first shift clocks a 1 (the stop bit)
February 1989 1-34

User's Guide
Signetics Microprocessor Products
WRITE
TO
SBUF ---~--~~~~~~--~~~--~--~r-~___~~~ TXD
PHASE 2 CLOCK
(lh fosc)
MODE2
(SMOD IS PCON.?) L.......-------+l
LOAD
SBUF
RXD
TRANSMIT
~--------------------------------------------~,---
February 1989 1-35

TIMER1
OVERFLOW
..~
WRITE
SBUF
TO --~---:==:Tr~~~~--~=----'~--~~l_ TXD
BIT
DETECTOR
RXD
TX
~
---t WRIT;:;E"T;:;O_S:.B..U"F;--.......-....JL----"L--..JL--Jl--JL--.JL--IL-..JL--.JIL---
-----. miiD
L SIPl I
TRANSMIT
STOP BIT
I
~
RXD BIT DETECTORl sr•• T.OT I I D6 L~STOP
RECEIVE SAMPLE TIMES BIT
SHIFT ~ __~L-_ _"l_ _~~_ _JL_ _'L_~l___~L_ _JL_ _L__ _ _
~RI~_________________________________________________________1r____
February 1989 1-36

(MSS) (LSS)
I EA Ix I x IES IET1 IEX' IETa I EXO I
Symbol Position Function
EA IE.? disables all interrupts. If EA = 0, no
interrupt will be acknowledged. If EA = 1,
~o--------------------~. each interrupt source is individually
enabled or disabled by setting or clearing
its enable bit.
1E.6 reserved
INTERRUPT
1E.5 reserved
SOURCES
ES IE.4 enables or disables the Serial Port
interrupt. If ES = 0, the Serial Port
interrupt is disabled.
~,------------------~. ETI IE.3 enables or disables the Timer 1 Overflow
interrupt. If ETI = 0, the Timer 1 interrupt
is disabled.
EXI IE.2 enables or disables External Interrupt 1. If
EXI = 0, External Interrupt 1 is disabled.
ETO IE.l enables or disables the Timer 0 Overflow
interrupt. If ETO = 0, the Timer 0 interrupt
is disabled.
~2~ enables or disables External Interrupt O. If
EXF2~ --(805~
EXO IE.O
EXO = 0, External Interrupt 0 is disabled.
Figure 37, 8051 Family Interrupt Sources Figure 38, Interrupt Enable Register (IE)
The Timer 0 and Timer 1 Interrupts are generated by

1FO and 1Fl, which are set by a rollover in their re-
spective Timer/Counter registers (except see Timer 0 in
Mode 3). When a timer interrupt is generated, the flag (MSS) (LSS)
that generated it is cleared by the on-chip hardware
\\hen the service routine is vectored to.
I x IX I X IPS IPT1 IPXl IPTO I PXO I
Symbol Position Function
The Serial Port Interrupt is generated by the logical OR IP.? reserved
of RI and TI. Neither of theses flags is cleared by hard- IP.6 reserved
ware when the service routine is vectored to. In fact, the
IP.5 reserved
service routine will normally have to determine whether
it was RI or TI that generated the interrupt, and the bit PS IP.4 defines the Serial Port Interrupt priority
will have to be cleared in software. level. PS-l programs It to the higher
priority level.
All of the bits that generate interrupts can be set or PTI IP.3 defines the Timer 1 Interrupt priority
level. PT1-1 programs It to the higher
cleared by software, with the same result as though it priority level.
had been set or cleared by hardware. That is, interrupts
can be generated or pending interrupts can be canceled PXl IP.2 defines the External Interrupt 1 priority
level. PX1-1 programs It to the higher
in software. priority level.
PTO IP.l defines the Timer 0 Interrupt priority
Each of these interrupt sources can be individually en- level. PTO-l programs It to the higher
abled or disabled by setting or clearing a bit in Special priority level.
Function Register IE (Figure 38). IE also contains a PXO IP.O defines the External Interrupt 0 priority
global disable bit, EA, which disables all interrupts at level. PXO-l programs It to the higher
once. priority level.
PRIORITY LEVEL STRUCTURE Figure 39, Interrupt Priority Register (lP)
Each interrupt source can also be individually pro- If two requests of different priority levels are received
grammed to one of two priority levels by setting or simultaneously, the request of higher priority level is
clearing a bit in Special Function Register IP (Figure serviced. If requests of the same priority level are re-
39). A low-priority interrupt can itself be interrupted by ceived simultaneously, an internal polling sequence de-
a high-priority interrupt, but not by another low-priority termines which request is serviced. Thus within each pri-
interrupt. A high-priority interrupt can't be interrupted ority level there is a second priority structure determined
by any other interrupt source. by the polling sequence as follows:
February 1989 1-37

Source Priority Within Level Thus the processor acknowledges an interrupt request by
1. IEO (highest) executing a hardware generated LCALL to the appropri-
2. TFO ate servicing routine. In some cases it also clears the
3. IEI flag that generated the interrupt, and in other cases it
4. TFI doesn't. It never clears the Serial Port or Timer 2 flags.
5. RI+TI (lowest) This has to be done in the user's software. It clears an
external interrupt flag (lEO or lEI) only if it was transi-
Note that the "priority within level" structure is only used tion-activated. The hardware-generated LCALL pushes
to resolve simultaneous requests of the same priority lev- the contents of the Program Counter on to the stack (but
el. it does not save the PSW) and reloads the PC with an
address that depends on the source of the interrupt being
The IP register contains a number of unimplemented vectored to, as shown below:
bits. IP.?, IP.6 and IP.S are reserved in the 80S1s. User
software should not write Is to these positions, since they Source Vector Address
may be used in other 8051 Family products. IEO 0003H
TFO OOOBH
HOW INTERRUPTS ARE HANDLED IEI 0013H
TFI OOlEH
The interrupt flags are sampled at SSP2 of every ma- RI+TI 0023H
chine cycle. The samples are polled during the following
machine cycle. If one of the flags was in a set condition Execution proceeds from that location until the RETI in-
at S5P2 of the preceding cycle, the polling cycle will struction is encountered. The RETI instruction informs
find it and the interrupt system will generate an LCALL the processor that this interrupt routine is no longer in
to the appropriate service routine, provided this progress, then pops the top two bytes from the stack and
hardware-generated LCALL is not blocked by any of the reloads the Program Counter. Execution of the inter-
following conditions: rupted program continues from where it left off.
1. An interrupt of equal or higher priority level is al- Note that a simple RET instruction would also have re-
ready in progress. turned execution to the interrupted program, but it would
2. The current (polling) cycle is not the final cycle in have left the interrupt control system thinking an inter-
the execution of the instruction in progress. rupt was still in progress.
3. The instruction in progress is RETI or any write to
the IE or IP registers. EXTERNAL INTERRUPTS
Any of these three conditions will block the generation of The external sources can be programmed to be level-
the LCALL to the interrupt service routine. Condition 2 activated or transition-activated by setting or clearing bit
ensures that the instruction in progress will be completed ITI or ITO in Register TCON. If ITx = 0, external in-
before vectoring to any service routine. Condition 3 en- terrupt x is triggered by a detected low at the INTx pin.
sures that if the instruction in progress is RETI or any If ITx = 1, external interrupt x is edge triggered. In this
access to IE or IP, then at least one more instruction mode if successive samples of the INTx pin show a high
will be executed before any interrupt is vectored to. in one cycle and a low in the next cycle, interrupt re-
quest flag lEx in TCON is set. Flag bit lEx then re-
The polling cycle is repeated with each machine cycle, quests the interrupt.
and the values polled are the values that were present at
SSP2 of the previous machine cycle. Note than that if an Since the external interrupt pins are sampled once each
interrupt flag is active but not being responded to for machine cycle, an input high or low should hold for at
one of the above conditions, if the flag is not still active least 12 oscillator periods to ensure sampling. If the ex-
when the blocking condition is removed, the denied internal interrupt is transition-activated, the external
terrupt will not be serviced. In other words, the fact that source has to hold the request pin high for at least one
the interrupt flag was once active but not serviced is not cycle, and then hold it low for at least one cycle. This is
remembered. Every polling cycle is new. done to ensure that the transition is seen so that inter-
rupt request flag lEx will be set. lEx will be auto-
The polling cycle/LCALL sequence is illustrated in Fig- matically cleared by the CPU when the service routine is
ure 40. called.
Note that if an interrupt of higher priority level goes ac- If the external interrupt is level-activated, the external
tive prior to SSP2 of the machine cycle labeled C3 in source has to hold the request active until the requested
Figure 40, then in accordance with the above rules it interrupt is actually generated. Then it has to deactivate
will be vectored to during CS and C6, without any in- the request before the interrupt service routine is com-
struction of the lower priority routine having been exe- pleted, or else another interrupt will be generated.
cuted.
February 1989 1-38

Signetlcs Microprocessor Products User's Guide
••· .... ·---C1-_.-II_.

I S5P2 I 58
1 ••
_ _ _ C2 _ _••- t I _ - - C 3 - -....... --c.--.. ..,I....
---C5--·····
·······lJL_n..fL_-\,~_-'-___''\u,_---''--_''\l~_---'-_ __
fYt
INTERRUPT INTERRUPT
INTERRUPTS
ARE POLLED
LONG CALL TO
INTERRUPT
VECTOR ADDRESS
INTERRUPT ROUTINE
GOES LATCHED
ACTIVE
This is the fastest possible response when C2 is the final cycle of an instruction other than RETI or an access to IE or IP.
Figure 40. Interrupt Response Timing Diagram
RESPONSE TIME cuted. One way to use this feature for single-step opera-
tion is to program one of the external interrupts (e.g.
The INfO and INT1 levels are inverted and latched into INfO) to be level-activated. The service routine for the
lEO and IE1 at S5P2 of every machine cycle. The values interrupt will terminate with the following code:
are not actually polled by the circuitry until the next
machine cycle. If a request is active and conditions are JNB P3.2,$ ;Wait Till INfO Goes High
right for it to be acknowledged, a hardware subroutine m P3.2,$ ;Wait Till INfO Goes Low
call to the requested service routine will be the next in- RETI ;Go Back and Execute One Instruction
struction to be executed. The call itself takes two cycles.
Thus, a minimum of three complete machine cycles Now if the INfO pin, which is also the P3.2 pin, is held
elapse between activation of an external interrupt request normally low, the CPU will go right into the External
and .the beginning of execution of the first instruction of Interrupt 0 routine and stay there until INTO is pulsed
the service routine. Figure 40 shows interrupt response (from low to high to low). Then it will execute RETI, go
timings. back to the task program, execute one instruction, and
immediately re-enter the External Interrupt 0 routine to
A longer response time. would result if the request is await the next pulsing of P3.2. One step of the task pro-
blocked by one of the 3 previously listed conditions. If an gram is executed each time P3.2 is pulsed. .
interrupt of equal or higher priority level is already in
progress, the additional wait time obviously depends on RESET
the nature of the other interrupt's service routine. If the
instruction in progress is not in its final cycle, the addi- The reset input is the RST pin, which is the input to a
tional wait time cannot be more the 3 cycles, since the Schmitt Trigger. A reset is accomplished by holding the
longest instructions (MUL and DIY) are only 4 cycles RST pin high for at least two machine cycles (24 oscilla-
long, and if the instruction in progress is RETI or an tor periods), while the oscillator is running. The CPU
access to IE or IP, the additional wait time cannot be responds by generating an internal reset, with the timing
more than 5 cycles (a maximum of one more cycle to shown in Figure 41.
complete the instruction in progress, plus 4 cycles to
complete the next instruction if the instruction is MUL The external reset signal is asynchronous to the internal
or DIV). clock. The RST pin is sampled during State 5 Phase 2
of every machine cycle. The port pins will maintain their
Thus, in a single-interrupt system, the response time is current activities for 19 oscillator periods after a logic 1
always more than 3 cycles and less than 9 cycles. has been sampled at the RST pin; that is, for 19 to 31
oscillator periods after the external reset signal has been
SINGLE-STEP OPERATION applied to the RST pin.
The 8051 interrupt structure allows single-step execution The internal reset algorithm writes Os to all the SFRs
with very little software overhead. As previously noted, an except the port latches, the Stack Pointer, and SBUF.
interrupt request will not be responded to while an inter- The port latches are initialized to FFH, the Stack Point-
rupt of equal priority level is still in progress, nor will it er to 07H, and SBUF is indeterminate. Table 11 lists the
be responded to after RETI until at least one other in- SFR reset values. The internal RAM is not affected by
struction has been executed. Thus, once an interrupt rou- reset. On power up the RAM content is indeterminate.
tine has been entered, it cannot be re-entered until at
least one instruction of the interrupted program is exe-
February 1989 1-39

r--- 12 OSC. PERIODS ----1

I 55 I 56 I 51 I 52 I S3 I 54 I S5 I S6 I S 1 I S2 I S3 I S4 I S5 I 56 I S 1 I 52 I S3 I S4 I
RST:
~/ 1111111117~
SAMPLE RST SAMPLE RST
CINTERNAL RESET SIGNAL
-
I
ALE:
PSEN:
po:
I
- 1 1 OSC. PERIODS -'"',,>--------19 OSC. PERIODS - - - - - -
Figure 41. Reset Timing
Table 11. 8051 SFR Reset Values

Note that the port pins ,viii be in a random state until
Register Reset Value the oscillator has started and the internal reset algorithm
PC OOOOH has written Is to them.
ACC OOH
B OOH With this circuit, reducing Vee quickly to 0 causes the
PSW OOH RST pin voltage to momentarily fall below OV. However,
SP 07H this voltage is internally limited, and will not harm the
DPTR OOOOH device.
PO-P3 FFH
IP XXXOOOOOB
IE OXXOOOOOB POWER-SAVING MODES OF OPERATION
TMOD OOH
TCON OOH For applications where power consumption is critical the
THO OOH CHMOSversion provides power reduced modes of opera-
TLO OOH tion as a standard feature. The power down mode in
TH1 OOH HMOS devices is no longer a standard feature.
TL1 OOH
SCON OOH CHMOS POWER REDUCTION MODE
SBUF Indeterminate
PCON (HMOS) OXXXXXXXB CHMOS versions have two power reducing modes, Idle
PCON (CHMOS) OXXXOOOOB and Power Down. The input through which backup power
is supplied during these operations is Vee. Figure 43
POWER-ON RESET shows the internal circuitry which implements these fea-
tures. In the Idle modes (IDL = 1), the oscillator con-
An automatic reset can be obtained when Vee is turned tinues to run and the Interrupt, Serial Port, and Timer
on by connecting the RST pin to Vee through a 1O,.u blocks continue to be clocked, but the clock signal is
capacitor and to Vss through an 8.2K resistor, providing gated off to the CPU. In Power Down (PD = 1), the os-
the Vee rise time does not exceed a millisecond and the cillator is frozen. The Idle and Power Down Modes are
oscillator start-up time does not exceed 10 milliseconds. activated by setting bits in Special Function Register
This power-on reset circuit is shown in Figure 42. The PCON. The address of this register is 87H. Figure 44
CHMOS devices do not require the 8.2K pulldown resis- details its contents.
tor, although its presence does no harm.
In the HMOS devices the PCON register only contains
When power is turned on, the circuit holds the RST pin SMOD. The other four bits are implemented only in the
high for an amount of time that depends on the value of CHMOS devices. User software should never write Is to
the capacitor and the rate at which it charges. To ensure unimplemented bits, since they may be used in other
a good reset, the RST pin must be high long enough to 8051 Family products.
allow the oscillator time to start-up (normally a few
msec) plus two machine cycles.
February 1989 1-40

(MSB) (lSB)
vee SMOO I I I GF1 GFO PO IOl
1
10u'_r-
vee t--
Symbol
SMOD
POlltlon
PCON.7
PCON.S
Name and Function
Double Baud rata bit. When set to a 1
and Timer 1 is used to generate baud
rate, and the Serial Port is used in
modes 1, 2, or 3.
(Reserved)
PCON.S (Reserved)
8051
PCON.4 (Reserved)
GFl PCON.3 General-purpose flag bit.
RST GFO PCON.2 General-purpose flag bit.
8.2K!! PO PCON.l Power Down bit. Setting this bit
activates power down operation.
IDL PCON.O Idle mode bit. Setting this bit activates
idle mode operation.
VSS
If 1 s are written to PO and IDL at the same time, PO takes
-l=- precedence. The reset value of PCON Is (OXXXOOOO).
In the H MaS devices the PCON register only contains
SMOD. The other four bits are Implemented only in the
CHMOS devices. User software should never write 1s to
Figure 42. Power On Reset Circuit unimplemented bits, since they may be used in future
products.
Figure 44. Power Control (PCON) Register
There are two ways to terminate the Idle. Activation of

any enabled interrupt will cause PCON.O to be cleared
by hardware, terminating the Idle mode. The interrupt
will be serviced, and following RETI, the next instruction
to be executed will be the one following the instruction
~~
that put the device into Idle.
The flag bits GFO and GF1 can be used to give an indi-
cation if an interrupt occurred during normal operation
XTAl 2 -= XTAL 1
or during an Idle. For example, an instruction that acti-
vates Idle can also set one or both flag bits. When Idle
is terminated by an interrupt, the interrupt service rou-
INTERRUPT.
f-......-<>SERIAL PORT,
tine can examine the flag bits. The other way of termi-
TIMER BLOCKS nating the Idle mode is with a hardware reset. Since the
clock oscillator is still running, the hardware reset needs
CPU to be held active for only two machine cycles (24 oscilla-
tor periods) to complete the reset.
The signal at the RST pin clears the IDL bit directly
and asynchronously. At this time the CPU resumes pro-
gram execution from where it left off; that is, at the in-
struction following the one that invoked the Idle Mode.
Figure 43. Idle and Power Down Hardware A, shown in Figure 41, two or three machine cycles of
program execution may take place before the internal
IDLE MODE reset algorithm takes control. On-chip hardware inhibits
access to the internal RAM during this time, but access
An instruction that sets PCON.O causes that to be the to the port pins is not inhibited. To eliminate the possi-
last instruction executed before going into the Idle bility of unexpected outputs at the port pins, the instruc-
mode, the internal clock signal is gated off to the CPU tion following the one that invokes Idle should not be one
but not to the Interrupt, Timer and Serial Port functions. that writes to a port pin or to external Data RAM.
The CPU status is preserved in its entirety; the Stack
Pointer, Program Counter, Program Status Word, Accu- POWER DOWN MODE
mulator, and all other registers maintain their data dur-
ing Idle. The port pins hold the logical states they had at An instruction that sets PCON.1 causes that to be the
the time Idle was activated. ALE and PSEN hold at log- last instruction executed before going into the Power
ic high levels. Down mode. In the Power Down mode, the on-chip os-
cillator is stopped. With the clock frozen, all functions
February 1989 1-41

are stopped, the contents of the on-chip RAM and Spe- Vee is restored to its normal operating level, and must
cial Function Registers are maintained. The port pins be held active long enough to allow the oscillator to re-
output the values held by their respective SFRs. The start and stabilize (normally less than lOmsec).
ALE and PSEN output are held low.
THE ON-CHIP OSCILLATORS
The only exit from Power Down is a hardware reset.
Reset redefines all the SFRs, but does not change the HMOS Versions
on-chip RAM.
The on-chip oscillator circuitry for the HMOS (-I and
In the Power Down mode of operation, Vee can be re- -II) members of the 8051 family is a single stage linear
duced to as low as 2V. Care must be taken, however, to inverter (Figure 45), intended for use as a crystal-
ensure that Vee is not reduced before the Power Down controlled, positive reactance oscillator (Figure 46). In
mode is invoked, and that Vee is restored to its normal this application the crystal is operated in its fundamental
operating level, before the Power Down mode is termi- response mode as an inductive reactance in parallel
nated. The reset that terminates Power Down also frees resonance with capacitance external to the crystal.
the oscillator. The reset should not be activated before
Vee
TO INTERNAL
nMlNGCKTS
XTAL2
XTAL1
?
SUBST.
Figure 45. On-Chip Oscillator In the HMOS Version of the 8051 Family
TO INTERNAL
nMINGCKTS
Vu
Il0l1
XTAU------
_ _-r---QUARTZ CRYSTAL
OR CERAMIC RESONATOR
C1 Cz
Figure 46. Using the HMOS On-Chip Oscillator
February 1989 1-42

The crystal specifications and capacitance values (C1 when a ceramic resonator is used.
and C2 in Figure 46) are not critical. 30pF can be used
in these positions at any frequency with good quality crys- To drive the CHMOS parts with an external clock '"
tals. A ceramic resonator can be used in place of the source, apply the external clock signal to XTAL1, and
crystal in cost-sensitive applications. When a ceramic leave XTAL2 float, as shown in Figure 50.
resonator is used, C1 and C2 are normally selected to
be of somewhat higher values, typically, 47pF. The manu- The reason for this change from the way the HMOS part
facturer of the ceramic resonator should be consulted for is driven can be seen by comparing Figures 46 and 48.
recommendation on the values of these capacitors. In the HMOS devices the internal timing circuits are
driven by the signal at XTZL2. In the CHMOS devices
To drive the HMOS parts with an external clock source, the internal timing circuits are driven by the signal at
apply the external clock signal to XTAL2, and ground XTALL
XTAL1, as shown in Figure 47. A pullup resistor may be
used (to increase noise margin), but is optional if VOH INTERNAL TIMING
of the driving gate exceeds the VIH minimum specifica-
tion of XTAL. Figures 51 through 54 show when the various strobe and
port signals are clocked internally. The figures do not
show rise and fall times of the signals, nor do they show
propagation delays between the XTAL2 signal and events
at other pins.
Rise and fall times are dependent on the external

loading that each pin must drive. They are often taken to
be something in the neighborhood of 10nsec, measured
Vee between 0.8V and 2.0V.
1011
Propagation delays are different for different pins. For a
given pin they vary with pin loading, temperature, Vee,
:>0-.....--4 XTALI and manufacturing lot. If the XTAL2 waveform is taken
as the timing reference, prop delays may vary from 25 to
XTAU 125nsec.
TTL
GATE Vss The AC Timings section of the data sheets do not refer-
wmt ence any timing to the XTAL2 waveform. Rather, they
TOTIIIoPOLE
OUTPUT relate the critical edges of control and input signals to
each other. The timings published in the data sheets in-
clude the effects of propagation delays under the speci-
Figure 47. Driving the HMOS 80S1 Family fied test conditions.
Parts with an External Clock
8051 PIN DESCRIPTIONS
CHMOS VERSIONS
ALEIPROG: Address Latch Enable output pulse for
The on-chip oscillator circuitry for the 8OC51BH, shown latching the low byte of the address during accesses to
in Figure 48, consists of a single stage linear inverter external memory. ALE is emitted at a constant rate of
intended for use as a. crystal-controlled, positive reac- 116 of the oscillator frequency, for external timing or
tance oscillator in the same manner as the HMOS parts. clocking purposes, even when there are no accesses to
However, there are some important differences. external memory. (However, one ALE pulse is skipped
during each access to external Data Memory.) This pin
One difference is that the SOC51BH is able to turn off is also the program pulse (PROG during EPROM pro-
its oscillator under software control (by writing a 1 to gramming).
the PD bit in PCON). Another difference is that, in the
8OC51BH, the internal clocking circuitry is driven by the PSEN: Program Store Enable is the read strobe to ex-
signal at XTAL1, whereas in the HMOS versions it is by ternal Program Memory. When the device is executing
the signal at XTAL2. out of external Program Memory, PSEN is activated
twice each machine cycle (except that two PSEN activa-
The ~eedback resistor Rf in Figure 48 consists of paral- tions are skipped during accesses to external Data
leled n-and p-channel PETs controlled by the PD bit, Memory). PSEN is not activated when the device is exe-
such that Rf is opened when PD - 1. The diodes D1 and cuting out of internal Program Memory.
D2, which act as clamps to Vee and Vss, are parasitic
to the Rf FETs. The oscillator can be used with the
same external components as the HMOS versions, as
shown in Figure 49. Typically, C1 = C2 - 30pF when
the feedback element is a quartz, and C1 - C2 - 47pF
February 1989 1-43

TO INTERNAL VCC
nMING CKTS
Figure 48. On-Chip Oscillator Circuitry in the CHMOS Versions of the 8051 Family
VCC
TO INTERNAL
nMINGCKTS
Vss
XTAL2·-----
1OC51
_..-,..--QUARTZ CRYSTAL
OR CERAMIC
RESONATOR
Figure 49. Using the CHMOS On-Chip Oscillator
EAlVpp: When EA is held high the CPU executes out of

internal Program Memory (unless the Program Counter
exceeds OFFFH in the 8051 or 80CS1). Holding EA low
forces the CPU to execute out of external memory re-
8OC51
gardlessof the Program Counter value. In the 8031AH,
Ne XTAL2 EA must be externally wired low. In the EPROM de~
vices, this pin also receives the programming supply
EXTERNAL
XTALI voltage (Vpp) during EPROM programming.
OSCILLATOR
SIGNAL
t
CMOS GATE
VSS
XTAL1: Input to the inverting oscillator amplifier.
.... XTAL2: Output from the inverting oscillator amplifier .
Figure 50. Driving the CHMOS Family

Parts with an External Clock Source
February 1989 1-44

User's Guide
Port 0: Port 0 is an 8-bit open drain bidirectional port. Port 3: Port 3 is an 8-bit bidirectional 110 port with in-
As an open drain output port, it can sink eight LS TIL ternal pultups. It also serves the functions of various
loads. Port 0 pins that have 1s written to them float, and special features of the 8051 Family as follows:
in that state will function as high impedance inputs. Port
o is also the multiplexed low-order address and data bus Port Pin Alternate Function
during accesses to external memory. In this application P3.0 RxD (serial input port)
it uses strong internal pullups when emitting 1s. Port 0 P3.1 TxD (serial output port)
also emits code bytes during program verification. In P3.2 INTO (external interrupt 0)
that application, external pullups are required. P3.3 INT1 (external interrupt 1)
P3.4 TO (timer 0 external input)
Port 1: Port 1 is an 8-bit bi-directional 110 port with in- P3.5 Tl (timer 1 external input)
ternal pullups. Port 1 pins that have Is written to them P3.6 WR (external data memory write strobe)
are pulled high by the internal pullups, and in that state P3.7 RD (external data memory read strobe)
can be used as inputs. As inputs, port 1 pins that are
externally being pulled low will source current because V cc: Supply voltage
of the internal pultups.
V ss: Circuit ground potential
Port 2: Port 2 is an 8-bit bidirectional 1/0 port with in-
ternal pullups. Port 2 emits the high-order address byte
during accesses to external memory that use 16-bit ad-
dresses. In this application, it uses the strong internal
pullups when emitting 1s.
I I
STATE 1 STATE
~I~ ~I~
21 STATE
~I~
'I I
41 STATE 'ISTATE 'ISTATE 1 STATE
STATE
~I~ ~I~ ~I~ ~I~ ~I~
21
XTAU:
ALI:
~: PCHOUT PCHOUT PCHOUT
Figure 51. External Program Memory Fetches
February 1989 1-45

ISTATt:
~1P2
41 STATt: 51 STATt: 61 STATt:
~1P2 ~1P2 ~1P2
'I STATE
~1P2
21 STATE 31 STATE 41 STATE 51
~1P2 ~1P2 ~1P2
XTAL2:
ALE:
iii:
PO:
PCHOR PCH OR
P2: P2SFR
DPH OR P2 SFR OUT
P2SFR
Figure 52. External Data Memory Read Cycle
I~1P241 ~1P251 ~1P261 ~1P2'I ~1P221 ~1P231 ~1P241 ~1P251

STATE STATE It.ATE STATE STATE STATE STATE STATE
XTAL2:
ALE:
WA:
F-
PCL OUT IF
IS EXTERNAL
Out ~
PO: DPL OR AI
OUT DATA OUT
P2 PCH OR
OPH OR P2 SFR OUT PCH OR
P2SFR P2SFR
Figure 53. External Data Memory Write Cycle
February 1989 1-46

I~1P2
STATE 41STATE SI STATE II/STATE 1 ISTATE 2/STATE 3/STATE 41 STATE 51
~1P2 ~1P2 ~1P2 ~1P2 ~1P2 ~1P2 ~1P2
XTALI:
~
'P1 PO,P1~
INPUTS SAMPLeD:
P2, P3, RST P2, P3, R8T=::rl.-
MaY PORT, IRC: OLD DATA NEW DATA
81I11ALPORT
IHIFTCLOCK
(MODE 0)
~ ~ RXD PIN SAMPLED RXD SAMPLED --l f--
Figure 54. Port Operation
February 1989 1-47

Section 1 8051 Family Programmer's Guide and Instruction Set
1. Register Banks 0-3: Locations 0 through IFH (32

PROGRAMMER'S GUIDE AND bytes). The device after reset defaults to register
INSTRUCTION SET bank O. To use the other register banks, the user
must select them in software. Each register bank
MEMORY ORGANIZATION contains eight I-byte registers 0 through 7. Reset ini-
tializes the stack pointer to location 07H and it is
PROGRAM MEMORY incremented once to start from location 08H which
is the first register (RO) of the second register bank.
The 8051 has separate address spaces for program and Thus in order to use more than one register bank,
data memory. The Program memory can be up to 64K the SP should be initialized to a different location of
bytes long. The lower 4K can reside on-chip. Figure 55 the RAM where it is not used for data storage. (i.e.
shows a map of the 8051 program memory. the higher part of the RAM).
2. Bit Addressable Area: 16 bytes have been assigned
The 8051 can address up to 64K bytes of data memory
for this segment, 20H-2FH. Each one of the 128
to the chip. The MOVX instruction is used to access the bits of this segment can be directly addressed
external data memory.
(0-7FH). The bits can be referred to in two ways
both of which are acceptable by most assemblers.
The 8051 has 128 bytes of on-chip RAM, plus a number
One way is to refer to their address (i.e. 0-7FH).
of Special Function Registers (SFRs). The lower 128
The other way is with reference to bytes 20H to
bytes of RAM can be accessed either by direct address-
2FH. Thus, bits 0-7 can also be referred to as bits
ing (MOY data addr) or by indirect addressing (MOY
20.0-20.7, and bits 8-FH are the same as
@Ri). Figure 56 shows the Data Memory organization.
21.0-21.7, and so on. Each of the 16 bytes in this
DIRECT AND INDIRECT ADDRESS AREA segment can also be addressed as a byte.
3. Scratch Pad Area: 30H through 7FH are available to
The 128 bytes of RAM which can be accessed by both the user as data RAM. However, if the data pointer
direct and indirect addressing can be divided into three has been initialized to this area, enough bytes should
segments as listed below and shown in Figure 57. be left aside to prevent SP data destruction.
Figure 56 shows the different segments of the on-chip

RAM.
~r-----------------, FFFFr-------------------~
&OK
BYTES
EXTERNAL
14K
---OR---~~ BYTES
EXTERNAL
1~~ __________________~
AND
~ooooFl________
_ INTERNAL
4K__
BYTES
__________ ~
oooo~------ ____________ ~
Figure 55. 8051 Program Memory
February 1989 1-48

~~----------------~
INTERNAL
FF,..-----------------, 14K
SFR. BYTES
DIRECT EXTERNAL
ADDRESSING
ONLY
10
7Fr-----------------~ ---AND--'"
DIRECT.
INDIRECT
ADORESBING
~~-------~ ~L-----------------J
Figure 56. 8051 Data Memory
1, .......
.-------- ellyln ------I~~II
7F
..
70 77
IF
..
10 IT
SCRATCH
IF
PAD
10 17
AREA
•
40 47
28 3F
30 37
••• 7F 2F BIT
ADDRESBABLE
20 0 ... 27 BEGMENT
1. 3 IF
10 2 17 REGISTER
oe 1 OF IANIC8
0 07
Figure 57. 128 Bytes of RAM Direct and Indirect Addressable
February 1989 1-49

User's Guide
Table 12. 8051, 80CSI Special Funcdon Registers Table 13. Contents of SFRs Arter a Reset
Name Address Register Value In Binary

Symbol
Accumulator OEOH *ACC OOOOOOOO
*ACC OOOOOOOO
·B B Register OFOH *B
Program Status Word ODOH *PSW 00000000
·PSW 00000111
SP Stack Pointer 81H SP
DPTR Data Pointer 2 Bytes DPTR
DPL Low Byte 82H DPL OOOOOOOO
DPH High Byte 83H DPH 00000000
·PO Port 0 80H *PO 11111111
·P1 Port 1 90H *Pl 11111111
*P2 Port 2 OAOH *P2 11111111
*P3 Port 3 OBOH *P3 11111111
*IP Interrupt Priority Control OB8H *IP xxxOOOOO
*IE Interrupt Enable Control OA8H *IE OXXOOOOO
TMOD Timer/counter Mode Control 89H TMOD 00000000
*TCON Timer/counter Control 88H *TCON 00000000
THO Timer/counter 0 High Byte 8CH THO 00000000
TLO Timer/counter 0 Low Byte 8AH TLO 00000000
TH1 Timer/counter 1 High Byte 8DH THI OOOOOOOO
TLI Timer/counter 1 Low Byte 8BH TLI OOOOOOOO
·SCON Serial Control 98H *SCON OOOOOOOO
SBUF Serial Data Buffer 99H SBUF Indeterminate
PCON Power Control 87H PCON HMOSOxxxxxxx
CHMOS OXXXOOOO
• = Bit addressable
x- Undefined
• = Bit addressable
I BY1U
F8 FF
FO B F7
E8 EF
EO ACC E7
DB DF
DO PSW D7
CB CF
CO C7
88 IP BF
BO P3 B7
A8 IE AF
AO P2 A7
98 SCON SBUF 9F
90 P1 97
88 TCON TMOD TLo TL1 THO TH1 8F
80 PO SIt DPL DPH POON 87
T
m..ABLE
Figure 58. 8051 SFR Memory Map
February 1989 1-50

Those SFRs that have their bits assigned for various functions are listed in this section. A brief description of each bit
is provided for quick reference. For more detailed information refer to the Architecture Chapter of this book.
PSW: PROGRAM STATUS WORD. BIT ADDRESSABLE.

CY AC Fa RS1 Rsa ov P
CY PSW.7 Carry Flag.
AC PSW.6 Auxiliary Carry Flag.
Fa PSW.5 Flag a available to the user for general purpose.
RSI PSW.4 Register Bank selector bit I (SEE NOTE I).
RSa PSW.3 Register Bank selector bit a (SEE NOTE I).
OV PSW.2 Overflow Flag.
PSW.I Usable as a general purpose flag.
P psw.a Parity flag. Set/cleared by hardware each instruction cycle to indicate an odd/even number of
'I' bits in the accumulator.
NOTE:
1. The value presented by RSO and RS1 selects the corresponding register bank.
RS1 RSO Register Bank Address
a a a OOH-07H
a 1 1 OBH-OFH
1 a 2 10H-17H
1 1 3 1BH-1FH
PCON: POWER CONTROL REGISTER. NOT BIT ADDRESSABLE.

SMOD GF1 GFO PO IDL
SMOD Double baud rate bit. If Timer I is used to generate baud rate and SMOD = I, the baud rate is doubled
when the Serial Port is used in modes I, 2, or 3.
Not implemented, reserved for future use.'
GF I General purpose flag bit.
GFa General purpose flag bit.
PD Power Down bit. Setting this bit activates Power Down operation in the 8aC5IBH. (Available only in
CHMOS).
IDL Idle Mode bit. Setting this bit activates Idle Mode operation in the 8aC51BH. (Available only in CHMOS).
If Is are written to PD and IDL at the same time, PD takes precedence.

·User software should not write 1s to reserved bits. These bits may be used in future 8051 products to invoke new
features.
February 1989 1-51

INTERRUPTS:
In order to use any of the interrupts in the 8051 Family, the following three steps must be taken.
1. Set the EA (enable all) bit in the IE register to 1.

2. Set the corresponding individual interrupt enable bit in the IE register to 1.
3. Begin the interrupt service routine at the corresponding Vector Address of that interrupt. See
Table below.
Interrupt Vector
Source Address
lEO 0OO3H
TFO OOOSH
IE1 0013H
TF1 001SH
RI & TI 0023H
In addition, for external interrupts, pins INTO and INTI (P3.2 and P3.3) must be set to I, and depending on whether
the interrupt is to be level or transition activated, bits ITO or ITI in the TCON register may need to be set to 1.
ITx = 0 level activated

ITx = 1 transition activated
IE: INTERRUPT ENABLE REGISTER. BIT ADDRESSABLE.

If the bit is 0, the corresponding interrupt is disabled. If the bit is I, the corresponding interrupt is enabled.
EA ES ET1 EX1 ETO EXO
EA IE.7 Disables all interrupts. If EA = 0, no interrupt will be acknowledged. If EA = 1, each interrupt
source is individually enabled or disabled by setting or clearing its enable bit.
IE.6 Not implemented, reserved for future use.'
IE.S Not implemented, reserved for future use.'
ES IE.4 Enable or disable the serial port interrupt.
ETI IE.3 Enable or disable the Timer I overflow interrupt.
EXI IE.2 Enable or disable External Interrupt 1.
ETO IE. I Enable or disable the Timer 0 overflow interrupt.
EXO lE.O Enable or disable External Interrupt O.
.User software should not write Is to reserved bits. These bits may be used in future 8051 products
to invoke new features.
February 1989 1-52

ASSIGNING HIGHER PRIORITY TO ONE OR MORE INTERRUPTS: I
In order to assign higher priority to an interrupt the corresponding bit in the IP register must be set to L I··,
Remember that while an interrupt service is in progress, it cannot be interrupted by a lower or same level interrupt.
PRIORITY WITHIN LEVEL:

Priority within level is only to resolve simultaneous requests of the same priority level
From high to low, interrupt sources are listed below:
lEO
TFO
lEI
TFI
RI or TI
IP: INTERRUPT PRIORITY REGISTER. BIT ADDRESSABLE.

If the bit is 0, the corresponding interrupt has a lower priority and if the bit is 1 the corresponding interrupt has a
higher priority.
1- I PS PT1 PX1 PTO PXO

IP.7 Not implemented, reserved for future use,·
IP. 6 Not implemented, reserved for future use.·
IP.5 Not implemented, reserved for future use.·
PS IP. 4 Dermes the Serial Port interrupt priority level.
PT I IP. 3 Defines the Timer I interrupt priority level.
PX I IP. 2 Defines External Interrupt I priority level.
PTO IP. I Defines the Timer 0 interrupt priority level.
PXO IP. 0 Defines the External Interrupt 0 priority level.
·User software should not write Is to reserved bits. These bits may be used in future 8051 products to invoke
new features.
February 1989 1-53

TCON: TIMER/COUNTER· CONTROL REGISTER. BIT ADDRESSABLE.

[ TF1 TR1 TFO TRO IE1 IT1 lEO ITO
TFI TCON. 7 Timer 1 overflow flag. Set by hardware when the Timer/Counter 1 overflows. Cleared by hard-
ware as processor vectors to the interrupt service routine.
TRI TCON. 6 Timer 1 run control bit. Set/cleared by software to turn Timer/Counter ION/OFF.
TFO TCON. 5 Timer 0 overflow flag. Set by hardware when the Timer/Counter 0 overflows. Cleared by hard-
ware as processor vectors to the service routine.
TRO TCON. 4 Timer 0 run control bit. Set/cleared by software to tum Timer/Counter 0 ON/OFF.
lEI TCON.3 External Interrupt 1 edge flag. Set by hardware when External Interrupt edge is detected.
Cleared by hardware when interrupt is processed.
ITt TCON. 2 Interrupt 1 type control bit. Set/cleared by software to specify falling edge/low level triggered
External Interrupt.
lEO TCON. 1 External Interrupt 0 edge flag. Set by hardware when External Interrupt edge detected. Cleared
by hardware when interrupt is processed.
ITO TCON. 0 Interrupt 0 type control bit. Set/cleared by software to specify falling edge/low level triggered
External Interrupt.
TMOD: TIMER/COUNTER MODE CONTROL REGISTER. NOT BIT

ADDRESSABLE.
I\0 GATE CIT I M1 MO I
)\:
GATE CIT I M1 MO
)
I
T
TIMER 1 TIMER 0
GATE When TRx (in TCON) is set and GATE = 1, TIMER/COUNTERx will run only while INTx pin is high
(hardware control). When GATE = 0, TIMER/COUNTERx will run only while TRx = 1 (software
control).
CIT Timer or Counter selector. Cleared for Timer operation (input from internal system clock). Set for Coun-
ter operation (input from Tx input pin).
Ml Mode selector bit. (NOTE 1)
MO Mode selector bit. (NOTE 1)
NOTE 1:
M1 MO Operating Mode
o o o 13-bit Timer (8048 compatible)
o 1 1 16-bit Timer/Counter
1 o 2 8-bit Auto-Reload Timer/Counter
1 1 3 (Timer 0) TLO is an 8-bit Timer/Counter controlled by the standard Timer 0
control bits, THO is an 8-bit Timer and is controlled by Timer 1 control bits.
3 (Timer 1) Timer/Counter 1 stopped.
February 1989 1-54

TIMER SET-UP
Tables 14 through 17 give some values for TMOD which can be used to set up Timer 0 in different modes. ,-i
!
It is assumed that only one timer is being used at a time. If it is desired to run Timers 0 and I simultaneously, in any
mode, the value in TMOD for Timer 0 must be ORed with the value shown for Timer 1 (Table 16 and 17).
For example, if it is desired to run Timer 0 in mode I GATE (external control), and Timer I in mode 2 COUNTER,
then the value that must be loaded into TMOD is 69H (09H from Table 14 ORed with 60H from Table 17).
Moreover, it is assumed that the user, at this point, is not ready to tum the timers on and will do that at a different
point in the program by setting bit TRx (in TCON) to 1.
TIMER/COUNTER 0
AsaTlmer:
Table 14
TMOD
TIMER 0 INTERNAL EXTERNAL
MODE
FUNCTION CONTROL CONTROL
(NOTE 1) (NOTE 2)
0 13-bit Timer OOH 08H
1 1S-bitTimer . 01H 09H
2 8-bit Auto-Reload 02H OAH
3 two 8-bit Timers 03H OSH
As a Counter:
Table 15
TMOD
COUNTER 0 INTERNAL EXTERNAL
MODE
(NOTE 1) (NOTE 2)
0 13-bit Timer 04H OCH
1 1S-bit Timer 05H OOH
2 8-bit Auto-Reload OSH OEH
3 one 8-bit Counter 07H OFH
NOTES:
1. The Timer is turned ON/OFF by setting/clearing bit TAO in the software.
2. The Timer is turned ON/OFF by the 1 to 0 transition on iN'i'O (P3.2) when TAO = 1
(hardware control).
February 1989 1-55

TIMER/COUNTER 1
As a Timer:
Table 16
TMOD
TIMER 1 INTERNAL EXTERNAL
MODE
(NOTE 1) (NOTE 2)
0 13-blt Timer OOH 80H
1 16-bit Timer 10H 90H
2 8-bit Auto-Reload 20H AOH
3 does not run 30H BOH
As a Counter:
Table 17
TMOD
COUNTER 1 INTERNAL EXTERNAL
MODE
(NOTE 1) (NOTE 2)
0 13-bit Timer 40H COH
1 16-bitTimer 50H DOH
2 8-bit Auto-Reload 60H EOH
3 not available - -
NOTES:
1. The Timer Is tumed ON/OFF by setting/clearing bit TR1 In the software.
2. The Timer Is tumed ON/OFF by the 1 to 0 transition on INTI (p3.3) when TRI = 1
(herdware control).
February 1989 1-56

SCON: (SOCON IN THE 83C652 AND 83C552) SERIAL PORT CONTROL REGISTER.
BIT ADDRESSABLE
I.
SMO SM1 SM2 REN TB8 RB8 TI RI
SMO SCON.7 Serial Port mode specifier. (NOTE 1).
SMI SCON.6 Serial Port mode specifier. (NOTE 1).
SM2 SCON.5 Enables the multiprocessor communication feature in modes 2 & 3. In mode 2 or 3, ifSM2 is set
to 1 then RI will not be activated if the received 9th data bit (RB8) is O. In mode I, if SM2 = 1
then RI will not be activated if a valid stop bit was not received. In mode 0, SM2 should be O.
(See Table 18).
REN SCON. 4 Set/Cleared by software to EnablelDisable reception.
TB8 SCON.3 The 9th bit that will be transmitted in modes 2 & 3. Set/Cleared by software.
RB8 SCON. 2 In modes 2 & 3, is the 9th data bit that was received. In mode I, if SM2 = 0, RB8 is the stop bit
that was received. In mode 0, RB8 is not used.
TI SCON. I Transmit interrupt flag. Set by hardware at the end of the 8th bit time in mode 0, or at the
beginning of the stop bit in the other modes. Mnst be cleared by software.
RI SCON.O Receive interrupt flag. Set by hardware at the end of the 8th bit time in mode 0, or halfway
through the stop bit time in the other modes (except see SM2). Must be cleared by software.
NOTE 1:
SMO SM1 Mode Description Baud Rate

o 0 0 SHIFT REGISTER Fosc.l12
o 1 1 8-Bit UART Variable
1 0 2 9-Bit UART Fosc.l64OR
Fosc.l32
3 9-BitUART Variable
SERIAL PORT SET-UP:

Table 18
MODE SCON SM2 VARIATION
0 10H
Single Processor
1 SOH
Environment
2 90H
(SM2 = 0)
3 DOH
0 NA
Multiprocessor
1 70H
Environment
2 BOH
(SM2 = 1)
3 FOH
GENERATING BAUD RATES
Serial Port in Mode 0:

Mode 0 has a fixed baud rate which is 1/12 of the oscillator frequency. To run the serial port in this mode none of
the Timer/Counters need to be set up. Only the SCON register needs to be defined.
Baud Rate = Osc Freq

12
Serial Port in Mode 1:

Mode 1 has a variable baud rate. The baud rate is generated by Timer 1.
February 1989 1-57

Signetics. Microprocessor Products User's Guide
USING TIMER/COUNTER 1 TO GENERATE BAUD RATES:

For this purpose, Timer 1 is used in mode 2 (Auto-Reload). Refer to Timer Setup section of this chapter.
B R K x Oscillator Freq.
aud ate = 32 x 12 x [256 - (TH1))
If SMOD = 0, then K = 1.
If SMOD = I, then K = 2. (SMOD is the PCON register).
Most of the time the user knows the baud rate and needs to know the reload value for TH 1.
Therefore, the equation to calculate THI can be written as:
KxOsc Freq.
TH1 = 256
384 x baud rate
TH 1 must be an integer value. Rounding off TH 1 to the nearest integer may not produce the desired baud rate. In
this case, the user may have to choose another crystal frequency.
Since the PCON register is not bit addressable, one way to set the bit is logical ORing the PCON register. (ie, ORL
PCON,#80H). The address of PCON is 87H.
SERIAL PORT IN MODE 2:

The baud rate is fixed in this mode and is 1/,2 or Y•• of the oscillator frequency depending on the value of the SMOD
bit in the PCON register.
In this mode none of the TimerS are used and the clock comes from the internal phase 2 clock.
SMOD = I, Baud Rate = 1/,2 Osc Freq.

SMOD = 0, Baud Rate = II•• Osc Freq.
To set the SMOD bit: ORL PCON, # SOH. The address of PCON is S7H.
SERIAL PORT IN MODE 3:

The baud rate in mode 3 is variable and sets up exactly the same as in mode 1.
February 1989 1-58

8051 FAMILY INSTRUCTION SET
Table 19. 8051 Instruction Set Summary

r---------------------------~
Interrupt Response Time: Refer to Hardware De-
.-----------------------------,
Oscillator
Mnemonic Description Byte
scription Chapter. Period
Instructions that Affect Flag Settlngs(1) ARITHMETIC OPERATIONS
ADD A,Rn Add register to 12
Instruction Flag Instruction Flag Accumulator
C OV AC C OV AC ADD A,direct Add direct byte to 2 12
ADD X X X ClRC 0 Accumulator
ADDC X X X CPlC X ADD A,@Ri Add indirect RAM 12
SUBB X X X ANlC,bit X to Accumulator
MUl 0 X ANl C,Ibit X ADD A,#data Add immediate 2 12
DIV 0 X ORlC,bit X data to
DA X ORl C,Ibit X Accumulator
RRC X MOVC,bit X ADDC A,Rn Add register to 12
RlC X CJNE X Accumulator
SETBC with Carry
(I}Note that operations on SFR byte address 208 or ADDC A,direct Add direct byte to 2 12
bit addresses 209-215 (i.e., the PSW or bits in the Accumulator
PSW) will also affect flag settings. with Carry
ADDC A,@Ri Add indirect 12
Note on instruction set and addressing modes: RAM to
Rn - Register R 7 - RO of the currently se- Accumulator
lected Register Baok. with Carry
direct - 8-bit internal data location's address. ADDC A,#data Add immediate 2 12
This could be ao Internal Data RAM data to Acc
location (0-127) or a SFR [i.e., I/O with Carry
port, control register, status register, SUBB A,Rn Subtract Register 12
etc. (128-255)]. from Acc with
@Ri - 8-bit intemai data RAM location (0- borrow
255) addressed indirectly through reg- SUBB A,direct Subtract direct 2 12
ister Rl or RO. byte from Acc
# data - 8-bit constant included in instruction. with borrow
# data 16 - 16-bit constant included in instruction. SUBB A,@Ri Subtract indirect 12
addr 16 - 16-bit destination address. Used by RAM from ACC
LCALL & UMP. A branch can be with borrow
anywhere within the 64K-byte Pro- SUBB A,#data Subtract 2 12
gram Memory address space. immediate data
addr 11 - ll-bit destination address. Used by from Acc with
ACALL & AJMP. The branch will be borrow
within the same 2K-byte page of pro- INC A Increment 12
gram memory as the first byte of the Accumulator
following instruction. INC Rn Increment register 1 12
rei - Signed (two's complement) 8-bit offset INC direct Increment direct 2 12
byte. Used by SJMP aod all condition- byte
al jumps. Range is -128 to + 127 INC @Ri Increment indirect 12
bytes relative to first byte of the fol- RAM
lowing instruction. DEC A Decrement 12
bit - Direct Addressed bit in Internal Data Accumulator
RAM or Special Function Register. DEC Rn Decrement 12
Register
DEC direct Decrement direct 2 12
byte
DEC @Ri Decrement 12
indirect RAM
All mnemonics copyrighted @ Intel Corporation 1980
February 1989 1-59

Table 19, 8051 Instruction Set Snmmary (Continned)

Oscillator Oscillator
Mnemonic Description Byte Mnemonic Description Byte
Period Period
ARITHMETIC OPERATIONS (Continued) LOGICAL OPERATIONS (Continued)
INC DPTR Increment Data 24 RL A Rotate 12
Pointer Accumulator Left
MUL AB Multiply A & B 48 RLC A Rotate 12
DIV AB DivideAbyB 48 Accumulator Left
DA A Decimal Adjust 12 through the Carry
Accumulator RR A Rotate 12
LOGICAL OPERATIONS Accumulator
ANL A,Rn AND Register to 12 Right
Accumulator RRC A Rotate 12
ANL A,direct AN D direct byte 2 12 Accumulator
to Accumulator Right through
ANL A,@Ri AND indirect 12 the Carry
RAM 10 SWAP A Swap nibbles 12
Accumulator within the
ANL A,#data AND immediate 2 12 Accumulator
data to DATA TRANSFER
Accumulator MOV A,Rn Move 12
ANL direct,A AND Accumulator 2 12 register to
to direct byte Accumulator
ANL direct, # data AND immediate 3 24 MOV A,direct Move direct 2 12
data to direct byte byte to
ORL A,Rn OR register to 12 Accumulator
Accumulator MOV A,@Ri Move indirect 12
ORL A,direct OR direct byte to 2 12 RAM to
Accumulator Accumulator
ORL A,@Ri OR indirect RAM 12 MOV A,#data Move 2 12
to Accumulator immediate
ORL A,#data OR immediate 2 12 data to
data to Accumulator
Accumulator MOV Rn,A Move 12
ORL direct,A OR Accumulator 2 12 Accumulator
to direct byte to register
ORL direct, # data OR immediate 3 24 MOV Rn,direct Move direct 2 24
data to direct byte byte to
XRL A,Rn Exclusive-OR 12 register
register to MOV Rn,#data Move 2 12
Accumulator immediate data
XRL A,direct Exclusive-OR 2 12 to register
direct byte to MOV direct,A Move 2 12
Accumulator Accumulator
XRL A,@Ri Exclusive-OR 12 to direct byte
indirect RAM to MOV direct,Rn Move register 2 24
Accumulator to direct byte
XRL A,#data Exclusive-OR 2 12 MOV direct,direct Move direct 3 24
immediate data to byte to direct
Accumulator MOV direct,@Ri Move indirect 2 24
XRL direct,A Exclusive-OR 2 12 RAM to
Accumulator to direct byte
direct byte MOV direct, # data Move 3 24
XRL direct, # data Exclusive-OR 3 24 immediate data
immediate data to direct byte
to direct byte MOV @Ri,A Move 12
CLR A Clear 12 Accumulator to
Accumulator indirect RAM
CPL A Complement 12 All mnemonics copyrighted ® Inlel Corporation 1980
Accumulator
February 1989 1-60

Si g netics Microprocessor Products User's Guide
Table 19. 8051 Instruction Set Summary (Continued)
Oscillator Oscillator
Mnemonic Description Byte Mnemonic Description Byte
Period Period
1-
DATA TRANSFER (Continued) BOOLEAN VARIABLE MANIPULATION
MOV @Ri,direct Move direct 2 24 CLR C Clear Carry 1 12
byte to CLR bit Clear direct bit 2 12
indirect RAM SETB C Set Carry 12
MOV @Ri,#data Move 2 12 SETB bit Set direct bit 2 12
immediate CPL C Complement 12
data to Carry
indirect RAM CPL bit Complement 2 "12
MOV DPTR, #datal6 Load Data 3 24 direct bit
Pointer with a ANL C,bit AND direct bit 2 24
16-bit constant to CARRY
MOVC A,@A+DPTR Move Code 24 ANL C,/bit AND complement 2 24
byte relative to of direct bit
DPTRto Acc to Carry
MOVC A,@A+PC Move Code 24 ORL C,bit OR direct bit 2 24
byte relative to to Carry
PC to Acc ORL C,/bit OR complement 2 24
MOVX A,@Ri Move 24 of direct bit
External to Carry
RAM (B-bit MOV C,bit Move direct bit 2 12
addr) to Acc to Carry
MOVX A,@DPTR Move 24 MOV bit,C Move Carry to 2 24
External direct bit
RAM (16-bit JC rei Jump if Carry 2 24
addr) to Acc is set
MOVX @Ri,A Move Acc to 24 JNC rei Jump if Carry 2 24
External RAM not set
(B-bit addr) JB bit,rel Jump if direct 3 24
MOVX @DPTR,A Move Acc to 24 Bit is set
External RAM JNB bit,rel Jump if direct 3 24
(16-bit addr) Bit is Not set
PUSH direct Push direct 2 24 JBC bit,rel Jump if direct 3 24
byte onto Bit is set &
stack clear bit
POP direct Pop direct 2 24 PROGRAM BRANCHING
byte from ACALL addrll Absolute 2 24
stack Subroutine
XCH A,Rn Exchange 12 Call
register with LCALL addr16 Long 3 24
Accumulator Subroutine
XCH A,direct Exchange 2 12 Call
direct byte RET Return from 24
with Subroutine
Accumulator RETI Return from 24
XCH A,@Ri Exchange 12 interrupt
indirect RAM AJMP addrll Absolute 2 24
with Jump
Accumulator WMP addr16 Long Jump 3 24
XCHD A,@Ri Exchange low- 12 SJMP rei Short Jump 2 24
order Digit (relative addr)
indirect RAM All mnemonics copyrighted © Intel Corporation 19BO
with Acc
February 1989 1-61

Table 19. 8051 Instruction Set Summary (Continued)

r---------------------------~ r---------------------------~
Oaclllator Oscillator
Mnemonic Description Byte Mnemonic Deacrlptlon Byte
Period Period
PROGRAM BRANCHING (Continued) PROGRAM BRANCHING (Continued)
JMP @A+DPTA Jump indirect 24 CJNE An,"'data,rel Compare 3 24
relative to the immediate to
DPTA register and
JZ rei Jump if 2 24 Jump if Not
Accumulator Equal
is Zero CJNE @Ai,"'data,rel Compare 3 24
JNZ rei Jump if 2 24 immediate to
Accumulator indirect and
is Not Zero Jump if Not
CJNE A,direct,rel Compare 3 24 Equal
direct byte to DJNZ An,rel Decrement 2 24
Acc and Jump register and
if Not Equal Jump if Not
CJNE A, '" data,rel Compare 3 24 Zero
immediate to DJNZ direct, rei Decrement 3 24
AccandJump direct byte
if Not Equal and Jump if
Not Zero
NOP No Operation 12
All mnemonics copyrighted © Intel Corporation 1980
February 1989 1-62

INSTRUCTION DEFINITIONS
ACALL addr11
Function: Absolute Call
Description: ACALL unconditionally calls a subroutine located at the indicated address. The instruction
increments the PC twice to obtain the address of the following instruction, then pushes the
16-bit result onto the stack (low-order byte first) and increments the Stack Pointer twice. The
destination address is obtained by successively concatenating the five high-order bits of the
incremented PC, opcode bits 7-5, and the second byte of the instruction. The subroutine called
must therefore start within the same 2K block of the program memory as the first byte of the
instruction following ACALL. No flags are affected.
Example: Initially SP equals 07H. The label "SUBRTN" is at program memory location 0345 H. After
executing the instruction,
ACALL SUBRTN
at location Ol23H, SP will contain 09H, internal RAM locations OSH and 09H will contain
25H and OIH, respectively, and the PC will contain 0345H.
Bytes: 2
Cycles: 2
Encoding: I a10 a9 a8 1 0 0 0 1 I a7 a6 a5 a4 a3 a2 a1 aO
Operation: ACALL
(PC) +- (PC) + 2
(SP) +- (SP) + 1
«SP» +- (PC7-O)
(SP) +- (SP) + I
«SP) +- (PCIS-S)
(PCIO-O) +- page address
February 1989 1-63

ADD A, <.rc-byte >
Function: Add
De.crlptlon: ADD adds the byte variable indicated to the Accumulator, leaving the result in the Accumula-
tor. The carry and auxiliary-carry flags are set, respectively, if there is a carry-out from bit 7 or
bit 3, and cleared otherwise. When adding unsigned integers, the carry flag indicates an
overflow occured.
OV is set if there is a carry-out of bit 6 but not out of bit 7, or a carry-out of bit 7 but not bit 6;
otherwise OV is cleared. When adding signed integers, OV indicates a negative number pro-
duced as the sum of two positive operands, or a positive sum from two negative operands.
Four source operand addressing modes are allowed: register, direct, register-indirect, or imme-
diate.
Example: The Accumulator holds OC3H (llOOOOllB) and register 0 holds OAAH (10 10 10 lOB). The
instruction,
ADD A,RO
will leave 6DH (01 101 IOIB) in the Accumulator with the AC flag cleared and both the carry
flag and OV set to 1.
ADD A,Rn
Byte.:
Cycle.:
Encoding: I 0 0 1 0 1 r r r
Operation: ADD
(A) ..- (A) + (Rn)
ADD A,dlrect
Byte.: 2
Cycle.:
Encoding: I 00 0 o1 0 1 direct address
Operation: ADD
(A) ..- (A) + (direct)
February 1989 1-64

ADD A,@Ri
Bytes:
Cycles:
Encoding:
1 00 1 0 011
Operation: ADD
(A) - (A) + «Rj))
ADD A, # data
Bytes: 2
Cycles:
Encoding: I 00 1 0 o1 0 0 immediate data
Operation: ADD
(A) -(A) + # data
ADDC A, < src-byte >
Function: Add with Carry

Description: ADDC simultaneously adds the byte variable indicated, the carry flag and the Accumulator
contents, leaving the result in the Accumulator. The carry and auxiliary-carry flags are set,
respectively, if there is a carry-out from bit 7 or bit 3, and cleared otherwise. When adding
unsigned integers, the carry flag indicates an overflow occured.
OV is set if there is a carry-out of bit 6 but not out of bit 7, or a carry-out of bit 7 but not out of
bit 6; otherwise OV is cleared. When adding signed integers, OV indicates a negative number
produced as the sum of two positive operands or a positive sum from two negative operands.
Four source operand addressing modes are allowed: register, direct, register-indirect, or imme-
diate.
Example: The Accumulator holds OC3H (llOOOOllB) and register 0 holds OAAH (lOlOJOlOB) with the
carry flag set. The instruction,
ADDC A,RO
will leave 6EH (01 1011 lOB) in the Accumulator with AC cleared and both the Carry flag and
OV set to I.
February 1989 1-65

ADDC A,Rn
Bytes:
Cycles:
Encoding: 1-1 _0_0_1_,--l_r_r_r-l1
Operation: ADDC
(A) - (A) + (C) + (R,J
ADDC A,dlrect
Bytes: 2
Cycles:
Encoding: 1-1 _0_0_1_,--0_1_0_1--, direct address
Operation: ADDC
(A) - (A) + (C) + (direct)
ADDC A,@RI
Bytes:
Cycles:
Encoding: 1-1 _O_O_l_-,-O_l_l_i--,1
Operation: ADDC
(A) - (A) + (C) + «Rv)
ADDC A,#data
Bytes: 2
Cycles:
Encoding: 1-1 _0_0_1_-,--0_1_0_0-, immediate data I

Operation: ADDC
(A) - (A) + (C) + #data
February 1989 1-66

AJMP addr11
Function: Absolute Jump

Description: AJMP transfers program execution to the indicated address, which is formed at run-time by
concatenating the high-order five bits of the PC (after incrementing the PC twice), opcode bits
7-5, and the second byte ofthe instruction. The destination must therefore be within the same
2K block of program memory as the first byte of the instruction following AJMP.
Example: The label "JMPADR" is at program memory location 0123H. The instruction,
AJMP JMPADR
is at location 0345H and will load the PC with 0123H.

Bytes: 2
Cycles: 2
Encoding: I a10 a9 a8 0 0 0 0 1 a7 a6 a5 a4 a3 a2 a1 aO
Operation: AJMP
(PC) +- (PC) + 2
(PCw.o) +- page address
ANL <dest-byte>,<src-byte>
Function: Logical-AND for byte variables

Description: ANL performs the bitwise logical-AND operation between the variables indicated and stores
the results in the destination variable. No flags are affected.
The two operands allow six addressing mode combinations. When the destination is the Accu-
mulator, the source can use register, direct, register-indirect, or immediate addressing; when
the destination is a direct address, the source can be the Accumulator or immediate data.
Note: When this instruction is used to modify an output port, the value used as the original
port data will be read from the output data latch, not the input pins.
Example: If the Accumulator holds OC3H (1IOOOOIIB) and register 0 holds 55H (OlOI010IB) then the
instruction,
ANL A,RO
will leave 4lH (OIOOOOOIB) in the Accumulator.
When the destination is a directly addressed byte, this instruction will clear combinations of
bits in any RAM location or hardware register. The mask byte determining the pattemofbits
to be cleared would either be a constant contained in the instruction or a value computed in
the Accumulator at run-time. The instruction,
ANL PI, #OIIIOOIIB
will clear bits 7, 3, and 2 of output port 1.
February 1989 1-67

Section 1· . 8051 Family Programmer's Guide and Instruction Set
ANL A,Rn
Bytes:
Cycl..:
Encoding: 1 0 1 01 1 1 r r r I
Operation: ANL
(A) - (A) A (Rn)
ANL A,dlrect
Byte.: 2
Cycles:
Encoding: 1 0101 1 0 1 0 1 1 direct address 1
Operation: ANL
(A) - (A) A (direct)
ANL A,@RI
Byte.:
Cycle.:
Encoding: 101011 011i l

Operation: ANL
(A) - (A) A «Ri»

ANL A,#data
Byte.: 2
Cycle.:
Encoding: 1 0101 1 01 001 immediate data 1
Operation: ANL
(A) - (A) A #data
ANL dlrect,A
Bytes: 2
Cycle.:
encoding: 1 010 1 1 001 0 1 I direcl address 1

Operation: ANL
(direct) - (direct) A (A)
February 1989 1-68

User's Guide
ANL direct, # data

Bytes: 3
Cycles: 2
Encoding: I0 1 0 1 0 0 1 1 direct address immediate data
Operation: ANL
(direct) +- (direct) /\ # data
ANL C,<src-blt>
Function: Logical-AND for bit variables

Description: If the Boolean value of the source bit is a logical 0 then clear the carry flag; otherwise leave the
carry flag in its current state. A slash (hI") preceding the operand in the assembly language
indicates that the logical complement of the addressed bit is used as the source value. but the
source bit itself is not affected. No other flags are affected.
Only direct addressing is allowed for the source operand.

Example: Set the carry flag if. and only if. P1.0 = 1. ACC. 7 = 1. and OV = 0:
MOV C,Pl.O ;LOAD CARRY WITH INPUT PIN STATE
ANL C.ACC.7 ;AND CARRY WITH ACCUM. BIT 7
ANL C,/OV ;AND WITH INVERSE OF OVERFLOW FLAG
ANL C,blt
Bytes: 2
Cycles: 2
Encoding: 11 000 00 1 0 bit address
Operation: ANL
(C) +- (C) /\ (bit)
ANL C,/blt
Bytes: 2
Cycles: 2
Encoding: 11 o1 0000 bit address
Operation: ANL
(C) +- (C) /\ --, (bit)
February 1989 1-69

CJNE < dest-byte > , < src-byte > , rei
Function: Compare and Jump if Not Equal.

Description: CINE compares the magnitudes of the first two operands, and branches if their values are not
equal. The branch destination is computed by adding the signed relative-displacement in the
last instruction byte to the PC, after incrementing the PC to the start of the next instruction.
The carry flag is set if the unsigned integer value of <dest-byte > is less than the unsigned
integer value of < src-byte > ; otherwise, the carry is cleared. Neither operand is affected.
The first two operands allow four addressing mode combinations, the Accumulator may be
compared with any directly addressed byte or immediate data, and any indirect RAM location
or working register can be compared with an immediate constant.
Example: The Accumulator contains 34H. Register 7 contains 56H. The first instruction in the se-
quence,
CINE R7,#60H, NOT_EQ

R7 = 6OH.
NOT.-EQ: JC REQJOW IFR7 < 6OH.
R7> 6OH.
sets the carry. flag and branches to the instruction at label NOT_EQ. By testing the carry flag,
this instruction determines whether R 7 is greater or less than 60H.
If the data being presented to Port I is also 34H, then the instruction,
WAIT: CINE A,PI,WAIT
clears the carry flag and continues with the next instruction in sequence, since the Accumula-
tor does equal the data read from PI. (If some other value was being input on PI, the program
will loop at this point until the PI data changes to 34H.)
CJNE A,direct,rel
Bytes: 3
Cycles: 2
Encoding: 110110101 direct address rei. address
Operation: (PC) - (PC) + 3

IF (A) < > (direct)
THEN
(PC) - (PC) + relative offset
IF (A) < (direct)

THEN
(C)-I
ELSE
(C)-O
February 1989 1-70

CJNE A, # data,rel
Bytes: 3
Cycles: 2
Encoding: 110110100 immediate data rei. address

IF (A) < > data
THEN
IF (A) < data

THEN
(C)-l
ELSE
(C)-O
CJNE Rn,#data,rel
Bytes: 3
Cycles: 2
Encoding: I1 0 1 1 1 r r r immediate data reI. address

IF (Rn) < > data
THEN
IF (Rn) < data

THEN
(C)-l
ELSE
(C)-O
CJNE @RI,#data,rel
Bytes: 3
Cycles: 2
Encoding: 11011011 immediate data reI. address

IF «Ri» < > data
THEN
IF «Ri» < data

THEN
(C)-l
ELSE
(C)-O
February 1989 1-71

CLR A
Function: Clear Accumulator

Description: The Accumulator is cleared (all bits reset to zero). No flags are affected.
Example: The Accumulator contains 5CH (01011100B). The instruction,
CLR A
will leave the Accumulator set to OOH (OOOOOOOOB).

Bytes:
Cycles:
Encoding: I1 1 1 0 1 0 0
Operation: CLR
(A)-O
CLR bit
Function: Clear bit

Description: The indicated bit is cleared (reset to zero). No other flags are affected. CLR can operate on the
carry flag or any directly addressable bit.
Example: Port 1 has previously been written with 5DH (01011 IOIB). The instruction,
CLR PI.2
will leave the port set to 59H (OIOII00IB).
CLR C
Bytes:
Cycles:
Encoding: I1 0 0 0 0 1 1
Operation: CLR
(C)-O
CLR bit
Bytes: 2
Cycles:
Encoding: I1 0 0 0 0 1 0 bit address
Operation: CLR
(bit) - 0
February 1989 1-72

CPL A
Function: Complement Accumulator

Description: Each bit of the Accumulator is logically complemented (one's complement). Bits which previ-
ously contained a one are changed to a zero and vice-versa. No flags are affected.
Example: The Accumulator contains 5CH (OlOlllOOB). The instruction,
CPL A
will leave the Accumulator set to OA3H (lOlOOOIIB).

Bytes:
Cycles:
Encoding: 11110100
Operation: CPL
(A) - - , (A)
CPL bit
Function: Complement bit

Description: The bit variable specified is complemented. A bit which had been a one is changed to zero and
vice-versa. No other flags are affected. CLR can operate on the carry or any directly address-
able bit.
Note: When this instruction is used to modify an output pin, the value used as the original data
will be read from the output data latch, not the input pin.
Example: Port I has previously been written with 5BH (OlOlllOlB). The instruction sequence,
CPL Pl.l
CPL P1.2
will leave the port set to 5BH (0101 101 IB).
CPL C
Bytes:
Cycles:
Encoding: 1_1_0_1_....>-_0_0_1_1-1
....
Operation: CPL
(C) - - , (C)
February 1989 1-73

CPL bit
Bytes: 2
Cycles:
Encoding: 1-1 _1_0_1_-,-_0_0_1_0-, bit address
Operation: CPL
(bit) +- -, (bit)
DA A
Function: Decimal-adjust Accumulator for Addition

Description: DA A adjusts the eight-bit value in the Accumulator resulting from the earlier addition of two
variables (each in packed-BCD format), producing two four-bit digits. Any ADD or ADDC
instruction may have been used to perform the addition.
If Accumulator bits 3-0 are·greater than nine (xxxxlOlO-xxxxllll), or if the AC flag is one,
six is added to the Accumulator producing the proper BCD digit in the low-order nibble. TIlls
internal addition would set the carry flag if a carry-out of the low-order four-bit field propagat-
ed through all high-order bits, but it would not clear the carry flag otherwise.
If the carry flag is now set, or if the four high-order bits now exceed nine (1010xxxx-lllxxxx),
these high-order bits are incremented by six, producing the proper BCD digit in the high-order
nibble. Again, this would set the carry flag if there was a carry-out of the high-order bits, but
wouldn't clear the carry. The carry flag thus indicates if the sum of the original two BCD
variables is greater than 100, allowing multiple precision decimal addition. OV is not affected.
All of this occurs during the one instruction cycle. Essentially, this instruction performs the
decimal conversion by adding OOH, 06H, 6OH, or 66H to the Accumulator, depending on
initial Accumulator and PSW conditions.
Note: DA A cannot simply convert a hexadecimal number in the Accumulator to BCD nota-
tion, nor does DA A apply to decimal subtraction.
February 1989 1-74

Example: The Accumulator holds the value 56H (01010110B) representing the packed BCD digits of the
decimal number 56. Register 3 contains the value 67H (OII00IIIB) representing the packed
BCD digits of the decimal number 67. The carry flag is set. The instruction sequence.
ADDC A,R3
DA A
will first perform a standard twos-complement binary addition, resulting in the value OBEH
(10111110) in the Accumulator. The carry and auxiliary carry flags will be cleared.
The Decimal Adjust instruction will then alter the Accumulator to the value 24H
(OOI00I00B), indicating the packed BCD digits of the decimal number 24, the low-order two
digits ofthe decimal sum of 56, 67, and the carry-in. The carry flag will be set by the Decimal
Adjust instruction, indicating that a decimal overflow occurred. The true sum 56, 67, and 1 is
124.
BCD variables can be incremented or decremented by adding 01H or 99H. If the Accumulator
initially holds 30H (representing the digits of 30 decimal), then the instruction sequence,
ADD A,#99H
DA A
will leave the carry set and 29H in the Accumulator, since 30 + 99 = 129. The low-order
byte of the sum can be interpreted to mean 30 - 1 = 29.
Bytes:
Cycles:
EnCOding: I1 1 0 1 0 1 0 0
Operation: DA
-contents of Accumulator are BCD
IF [[(A3-O) > 9) V [(AC) = 111
THEN(A3-O) +- (A3-O) + 6
AND
IF [[(A74) > 9) V [(C) = 111

THEN (A7-4) +- (A74) +6
February 1989 1-75

Section 1 8051 F~mily Programmer's Guide and Instruction Set
DEC byte
Function: Decrement
Description: The variable indicated is decremented by I. An original value of OOH will underflow to OFFH.
No flags are affected. Four operand addressing modes are allowed: accumulator, register,
direct, or register-indirect.
£xample: Register 0 contains 7FH (OlllllllB). Internal RAM locations 7EH and 7FH contain OOH
and 4OH, respectively. The instruction sequence,
DEC @RO
DEC RO
DEC @RO
will leave register 0 set to 7EH and internal RAM locations 7EH and 7FH set to OFFH and
3FH.
DEC A
Bytes:
Cycles:
Encoding: 100010100
Operation: DEC
(A) - (A) - 1
DEC Rn
Bytes:
Cycles:
Encoding: 10001 1rrr
Operation: DEC
(Rn) - (Rn) - 1
February 1989 1-76

DEC direct
Bytes: 2
Cycles:
Encoding: ,-I _0_0_0_-,--0_1_0_1-, direct address
Operation: DEC
(direct) +- (direct) -
DEC @RI
Bytes:
Cycles:
Encoding: 1 °°° ° 1 1
Operation: DEC
«Ri» +- «Ri» - I
DIV AB
Function: Divide
Description: DIV AB divides the unsigned eight-bit integer in the Accumulator by the unsigned eight-bit
integer in register B. The Accumulator receives the integer part of the quotient; register B
receives the integer remainder. The carry and OV flags will be cleared.
Exception: if B had originally contained OOH, the values returned in the Accumulator and B-
register will be undefined and the overflow flag will be set. The carry flag is cleared in any
case.
Example: The Accumulator contains 251 (OFBH or lIIIIOIIB) and B contains 18 (12H or 000100 lOB).
The instruction,
DIV AB
will leave 13 in the Accumulator (ODH or OOOOllOIB) and the value 17 (llH or OOOIOOOIB)
in B, since 251 = (13 X 18) + 17. Carry and OV will both be cleared.
Bytes:
Cycles: 4
Encoding: 1 1 °°° ° °° 1
Operation: DIV
(A)15-8 +- (A)/(B)
(Bh-o
February 1989 1-77

DJNZ < byte> , < rel-addr >
Function: Decrement and Jump if Not Zero

Description: DJNZ decrements the location indicated by I, and branches tothe address indicated by the
second operand if the resulting value is not zero. An original value of OOH will underflow to
OFFH. No flags are affected. The branch destination would be computed by adding the signed
relative-displacement value in the last instruction byte to the PC, after incrementing the PC to
the first byte of the following instruction.
The location decremented may be a register or directly addressed byte.
Example: Internal RAM locations 40H, 50H, and 60H contain the values OIH, ?OH, and 15H, respec-
tively. The instruction sequence,
DJNZ 40H,LABEL_l
DJNZ 50H,LABEL_2
DJNZ 60H,LABEL_3
will cause a jump to the instruction at label LABEL_2 with the values OOH, 6FH, and 15H in
the three RAM locations. The first jump was not taken because the result was zero.
This instruction provides a simple way of executing a program loop a given number of times,
or for adding a moderate time delay (from 2 to 512 machine cycles) with a single instruction.
The instruction sequence,
MOV R2,#8
TOGGLE: CPL Pl.?
DJNZ R2,TOGGLE
will toggle Pl.? eight times, causing four output pulses to appear at bit 7 of output Port I.
Each pulse will last three machine cycles; two for DJNZ and one to alter the pin.
DJNZ Rn,rel
Bytes: 2
Cycles: 2
Encoding: L.1_1_1_0_1......L_1_ r_r_ r ..J reI. address
Operation: DJNZ
(PC) - (PC) + 2
(Rn) - (Rn) - I
IF (Rn) > 0 or (Rn) < 0
THEN
(PC) - (PC) + rel
February 1989 1-78

User's Guide
DJNZ dlrect,rel
Bytes: 3
Cycles: 2
Encoding: I1 1 0 1 0 1 0 1 direct address reI. address
Operation: DJNZ
(PC) +- (PC) + 2
(direct) +- (direct) -
IF (direct) > 0 or (direct) < 0
THEN
(PC) +- (PC) + reI
INC <byte>
Function: Increment
Description: INC increments the indicated variable by I. An original value of OFFH will overflow to OOH.
No flags are affected. Three addressing modes are allowed: register, direct, or register-indirect.
Example: Register 0 contains 7EH (011 II II lOB). Internal RAM locations 7EH and 7FH contain OFFH
and 4OH, respectively. The instruction sequence,
INC @RO
INC RO
INC @RO
will leave register 0 set to 7FH and internal RAM locations 7EH and 7FH holding (respective-
ly) OOH and 4tH.
INC A
Bytes:
Cycles:
Encoding: 10000 I0 1 0 0
Operation: INC
(A) +- (A) +
February 1989 1-79

INC Rn
Bytes:
Cycles:
Encoding: I 0000 I 1 r r r
Operation: INC
(Rn)- (Rn) +
INC direct
Bytes: 2
Cycles:
Encoding: I 000 0 I 0 1 0 1 I direct address
Operation: INC
(direct) - (direct) +
INC @RI
Bytes:
Cycles:
Encoding: I 0000 I 011

Operation: INC
((Ri» - ((Ri» + 1
INC DPTR
Function: Increment Data Pointer

Description: Increment the 16-bit data pointer by I. A 16-bit increment (modulo 2 16) is performed; an
overflow of the low-order byte of the data pointer (DPL) from OFFH to OOH will increment
the high-order byte (DPH). No flags are affected.
This is the only 16-bit register which can be incremented.

Example: Registers DPH and DPL contain 12H and OFEH. respectively. The instruction sequence.
INC DPTR
INC DPTR
INC DPTR
will change DPH and DPL to I3H and OlH.

Bytes:
Cycles: 2
Encoding: I1 0 1 0 0 0 1 1
Operation: INC
(DPTR) - (DPTR) + I
February 1989 1-80

JB blt,rel
Function: Jump if Bit set

Description: If the indicated bit is a one, jump to the address indicated; otherwise proceed with the next
instruction. The branch destination is computed by adding the signed relative-displacement in
the third instruction byte to the PC, after incrementing the PC to the first byte of the next
instruction. The bit tested is not modified. No flags are affected.
Example: The data present at input port I is I 100 10 lOB. The Accumulator holds 56 (010101 lOB). The
instruction sequence,
JB P1.2,LABELl
JB ACC.2,LABEL2
will cause program execution to branch to the instruction at label LABEL2.

Bytes: 3
Cycles: 2
Encoding: I0 0 1 0 0 0 0 0 bit address reI. address
Operation: JB
(PC) +- (PC) + 3
IF (bit) = I
THEN
(PC) +- (PC) + rei
JBC bit,rel
Function: Jump if Bit is set and Clear bit

Description: If the indicated bit is one, branch to the address indicated; otherwise proceed with the next
instruction. The bit will not be cleared if it is already a zero. The branch destination is comput-
ed by adding the signed relative-displacement in the third instruction byte to the PC, after
incrementing the PC to the first byte of the next instruction. No flags are affected.
Note: When this instruction is used to test an output pin, the value used as the original data
will be read from the output data latch, not the input pin.
Example: The Accumulator holds 56H (01010ll0B). The instruction sequence,
JBC ACC.3,LABELl
JBC ACC.2,LABEL2
will cause program execution to continue at the instruction identified by the label LABEL2,
with the Accumulator modified to 52H (0 101 00 lOB).
February 1989 1-81

Bytes: 3
Cycles: 2
Encoding: 1..._0_0_0_-,-0_0_0_0-, bit address reI. address
Operation: JBC
(PC) +- (PC) + 3
IF (bit) = 1
THEN
(bit) +- 0
(PC) +- (PC) + rei
JC rei
Function: Jump if Carry is set

Description: If the carry flag is set, branch to the address indicated; otherwise proceed with the next
the second instruction byte to the PC, after incrementing the PC twice. No flags are affected.
Example: The carry flag is cleared. The instruction sequence,
JC LABELl
CPL C
JC LABEL 2
will set the carry and cause program execution to continue at the instruction identified by the
label LABEL2.
Bytes: 2
Cycles: 2
Encoding: I ° 1 0 0 I °0 0 0 I reI. address
Operation: JC
(PC) +- (PC) + 2
IF (C) = 1
THEN
(PC) +- (PC) + reI
February 1989 1-82

JMP @A+DPTR
Function: Jump indirect

Description: Add the eight-bit unsigned contents of the Accumulator with the sixteen-bit data pointer, and
load the resulting sum to the program counter. This will be the address for subsequent instruc-
tion fetches. Sixteen-bit addition is performed (modulo 2 16): a carry-out from the low-order
eight bits propagates through the higher-order bits. Neither the Accumulator nor the Data
Pointer is altered. No flags are affected.
Example: An even number from 0 to 6 is in the Accumulator. The following sequence of instructions will
branch to one of four AJMP instructions in a jump table starting at JMP_ TBL:
MOV DPTR,#JMP_TBL
JMP @A+DPTR
AJMP LABELO
AJMP LABELl
AJMP LABEL2
AJMP LABEL3
If the Accumulator equals 04H when starting this sequence, execution will jump to label
LABEL2. Remember that AJMP is a two-byte instruction, so the jump instructions start at
every other address.
Bytes:
Cycles: 2
Encoding: 101110011
Operation: JMP
(PC) - (A) + (DPTR)
February 1989 1-83

JNB blt,rel
Function: Jump if Bit Not set

Description: If the indicated bit is a zero, branch to the indicated address; otherwise proceed with the next
the third instruction byte to the PC, after incrementing the PC to the first byte of the next
instruction. The bit tested is not modified. No flags are affected.
Example: The data present at input port 1 is llOOlOlOB. The Accumulator holds 56H (010101 lOB). The
instruction sequence,
JNB P1.3,LABELl
JNB ACC.3,LABEL2
will cause program execution to continue at the instruction at label LABEL2.

Bytes: 3
Cycles: 2
Encoding: 10 0 1 1 0 0 0 0 bit address reI. address
Operation: JNB
(PC) +- (PC) + 3
IF (bit) = 0
THEN (PC) +- (PC) + reI.
JNC rei
Function: Jump if Carry not set

Description: If the carry flag is a zero, branch to the address indicated; otherwise proceed with the next
the second instruction byte to the PC, after incrementing the PC twice to point to the next
instruction. The carry flag is not modified.
Example: The carry flag is set. The instruction sequence,
INC LABELl
CPL C
JNC LABEL2
will clear the carry and cause program execution to continue at the instruction identified by
the label LABEL2.
Bytes: 2
Cycles: 2
Encoding: 101010000 reI. address
Operation: JNC
(PC) +- (PC) + 2
IF (C) = 0
THEN (PC) +- (PC) + reI
February 1989 1-84

JNZ rei
Function: Jump if Accumulator Not Zero

Description: If any bit of the Accumulator is a one, branch to the indicated address; otherwise proceed with
the next instruction. The branch destination is computed by adding the signed relative-dis-
placement in the second instruction byte to the PC, after incrementing the PC twice. The
Accumulator is not modified. No flags are affected.
Example: The Accumulator originally holds DOH. The instruction sequence,
JNZ LABELl
INC A
JNZ LABEL2
will set the Accumulator to OIH and continue at label LABEL2.

Bytes: 2
Cycles: 2
Encoding: LI_0__1_1--1._0_0_0_0-, reI. address
Operation: JNZ
(PC) - (PC) + 2
IF (A) =F °
THEN (PC) - (PC) + rei
JZ rei
Function: Jump if Accumulator Zero

Description: If all bits of the Accumulator are zero, branch to the address indicated; otherwise proceed with
the next instruction. The branch destination is computed by adding the signed relative-dis-
placement in the second instruction byte to the PC, after incrementing the PC twice. The
Accumulator is not modified. No flags are affected.
Example: The Accumulator originally contains OIH. The instruction sequence,
JZ LABELl
DEC A
JZ LABEL2
will change the Accumulator to DOH and cause program execution to continue at the instruc-
tion identified by the label LABEL2.
Bytes: 2
Cycles: 2
Encoding: 1 ° 1 1 ° ° °° 0 1 reI. address
Operation: JZ
(PC) - (PC) + 2
IF (A) = °
THEN (PC) - (PC) + rei
February 1989 1-85

LCALL addr16 (Not implemented in 8xC751 and 8xC752)
Function: Long call

Description: LCALL calls a subroutine located at the indicated address. The instruction adds three to the
program counter to generate the address of the next instruction and then pushes the 16-bit
result onto the stack (low byte first), incrementing the Stack Pointer by two. The high-order
and low-order bytes of the PC are then loaded, respectively, with the second and third bytes of
the LCALL instruction. Program execution continues with the instruction at this address. The
subroutine may therefore begin anywhere in the full 64K-byte program memory address space.
No flags are affected.
Example: Initially the Stack Pointer equals 07H. The label "SUBRTN" is assigned to program memory
location 1234H. After executing the instruction,
LCALL SUBRTN
at location 0123H, the Stack Pointer will contain 09H, internal RAM locations OSH and 09H
will contain 26H and 01H, and the PC will contain 1235H.
Bytes: 3
Cycles: 2
Encoding: LI _0_0_0_....l.-0_0_1_0...J addr1S-addrB addr7-addrO
Operation: LCALL
(PC) +- (PC) + 3
(SP) +- (SP) + 1
«SP» +- (PC7-O)
(SP) +- (SP) + I
«SP» +- (PCIS-S)
(PC) +- addf!5.0
LJMP addr16 (Implemented in 87C751 and 87C752, for use in in-circuit emulation).
Function: Long Jump

Description: UMP causes an unconditional branch to the indicated address, by loading the high-order and
low-order bytes of the PC (respectively) with the second and third instruction bytes. The
destination may therefore be anywhere in the full 64K program memory address space. No
flags are affected.
Example: The label "JMPADR" is assigned to the instruction at program memory location 1234H. The
instruction,
UMP JMPADR
at location 0123H will load the program counter with 1234H.

Bytes: 3
Cycles: 2
Encoding: 1000010010 addr1S-addrB addr7 -addrO
Operation: UMP
(PC) +- addrl5-O
February 1989 1-86

MOV < dest-byte > , < src-byte >
Function: Move byte variable

Description: The byte variable indicated by the second operand is copied into the location specified by the
first operand. The source byte is not affected. No other register or flag is affected.
This is by far the most flexible operation. Fifteen combinations of source and destination
addressing modes are allowed.
Example: Internal RAM location 30H holds 4OH. The value of RAM location 40H is 10H. The data
present at input port I is llOOlOlOB (OCAH).
MOV RO,#30H ;RO <= 30H

MOV A,@RO ;A <= 40H
MOV Rl,A ;Rl < = 40H
MOV R,@Rl ;B <= IOH
MOV @Rl,Pl ;RAM (40H) < = OCAH
MOV P2,Pl ;P2 #OCAH
leaves the value 30H in register 0, 40H in both the Accumulator and register 1, IOH in register
B, and OCAH (11001010B) both in RAM location 40H and output on port 2.
MOV A,Rn
Bytes:
Cycles:
Encoding: 11 1 1 0 1r r r
Operation: MOV
(A) -(Rn)
"MOV A,dlrect
Bytes: 2
Cycles:
Encoding: 11 1 1 0 01 0 1 direct address
Operation: MOV
(A) - (direct)
"MOV A,ACC Is not a valid Instruction.
February 1989 1-87

MOV A,@RI
Bytes:
Cycles:
Encoding: 11 1 1 0 o1
Operation: MOV
(A) - «Ri»
MOV A,#data
Bytes: 2
Cycles:
Encoding: 10 1 1 1 o1 0 0 immediate data
Operation: MOV
(A)- #data
MOV Rn,A
Bytes:
Cycles:
Encoding: I1 11 1 1 r r r
Operation: MOV
(Rn) - (A)
MOV Rn,dlrect
Bytes: 2
Cycles: 2
Encoding: 11 010 1 r r r direct addr.
Operation: MOV
(Rn) - (direct)
MOV Rn,#data
Bytes: 2
Cycles:
Encoding: 01 1 1 1 r r r immediate data

1
Operation: MOV
(Rn) - #data
February 1989 1-88

Si 9 netics M icrop rocessor Prod ucts User's Guide
MOV dlrect,A
Bytes: 2
Cycles:
Encoding: I 1111 0 10 1 direct address
Operation: MOY
(direct) - (A)
MOV dlrect,Rn
Bytes: 2
Cycles: 2
Encoding: 11 000 1 r r r direct address
Operation: MOY
(direct) - (Rn)
MOV dlrect,dlrect
Bytes: 3
Cycles: 2
Encoding: 11 000 o 1 0 1 dir. addr. (src) dir. addr. (dest)
Operation: MOY
(direct) - (direct)
MOV dlrect,@RI
Bytes: 2
Cycles: 2
Encoding: 11 000 o 1 direct addr.
Operation: MOY
(direct) - «Ri»
MOV direct, # data
Bytes: 3
Cycles: 2
Encoding: 101 1 1 o10 1 direct address immediate data 1
Operation: MOY
(direct) - #data
February 1989 1-89

MOV @RI,A
Bytes:
Cycles:
Encoding: 1 1 1 1 1 o1
Operation: MOV
«Ri» - (A)
MOV @RI,dlrect
Bytes: 2
Cycles: 2
Encoding: 11 0 1 0 o1 direct addr.
Operation: MOV
«Ri» - (direct)
MOV @RI,#data
Bytes: 2
Cycles:
Encoding: 101 11 o 1 ·1 immediate data I

Operation: MOV
«RJ» - #data
MOV <dest-blt>, <src-blt>

Function: Move bit data
Deacrlptlon: The Boolean variable indicated by the second operand is copied into the location specified by
thef1I'St operand. One of the operands must be the carry flag; the other may be any directly
addressable bit. No other register or flag is affected.
Example: The carry flag is originally set. The data present at input Port 3 is llOOOHilB. The data
previously written to output Port 1 is 35H (OOllOlOlB).
MOV P1.3,C
MOV C,P3.3
MOV P1.2,C
will leave the carry cleared and change Port 1 to 39H (OOlllOOlB).
February 1989 1-.90

MOY C,blt
Bytes: 2
Cycles:
Encoding: 11 o1 0 001 0 bit address
Operation: MOY
(C) +- (bit)
MOY blt,C
Bytes: 2
Cycles: 2
Encoding: 11 0 0 1 001 0 bit address
Operation: MOY
(bit) +- (C)
MOY DPTR,#data16
Function: Load Data Pointer with a 16-bit constant

Description: The Data Pointer is loaded with the 16-bit constant indicated. The 16-bit constant is loaded
into the second and third bytes of the instruction. The second byte (DPH) is the high-order
byte, while the third byte (DPL) holds the low-order byte. No flags are affected.
This is the only instruction which moves 16 bits of data at once.

Example: The instruction,
MOY DPTR,#1234H
will load the value 1234H into the Data Pointer: DPH will hold 12H and DPL will hold 34H.
Bytes: 3
Cycles: 2
EncodIng: 110010000 immed. data15-8 immed. data7-0
OperatIon: MOY
(DPTR) +- #datalS"()
DPH 0 DPL +- #datalS_S 0 #data7"()
February 1989 1-91

MOVC A,@A+ <base-reg>
Function: Move Code byte

Description: The MOVC instructions load the Accumulator with a code byte, or constant from program
memory. The address of the byte fetched is the sum of the original unsigned eight-bit Accumu-
lator contents and the contents of a sixteen-bit base register, which may be either the Data
Pointer or the PC. In the latter case, the PC is incremented to the address of the following
instruction before being added with the Accumulator; otherwise the base register is not al-
tered. Sixteen-bit addition is performed so a carry-out from the low-order eight bits may
propagate through higher-order bits. No flags are affected.
Example: A value between 0 and 3 is in the Accumulator. The following instructions will translate the
value in the Accumulator to one of four values defined by the DB (define byte) directive.
RELJC: INC A
MOVC A,@A+PC
RET
DB 66H
DB 77H
DB 88H
DB 99H
If the subroutine is called with the Accumulator equal to OIH, it will return with 77H in the
Accumulator. The INC A before the MOVC instruction is needed to "get around" the RET
instruction above the table. If several bytes of code separated the MOVC from the table, the
corresponding number would be added to the Accumulator instead.
MOVC A,@A+DPTR
Bytes: I
Cycles: 2
Encoding: 11 0 0 1 0 0 1 1
Operation: MOVC
(A) +- «A) + (DPTR))
MOVC A,@A + PC
Bytes:
Cycles: 2
Encoding: 11000 0011
Operation: MOVC
(PC) +- (PC) + I
(A) +- «A) + (PC))
February 1989 1-92

Si gnetics Microprocessor Prod ucts User's Guide
MOVX <dest-byte>,<src-byte> (Not implemented in 8xC751 and 8xC752)
Function: Move External

Description: The MOVX instructions transfer data between the Accumulator and a byte of external data
memory, hence the "X" appended to MOV. There are two types of instructions, differing in
whether they provide an eight-bit or sixteen-bit indirect address to the external data RAM.
In the first type, the contents of RO or R I in the current register bank provide an eight-bit
address multiplexed with data on PO. Eight bits are sufficient for external I/O expansion
decoding or for a relatively small RAM array. For somewhat larger arrays, any output port
pins can be used to output higher-order address bits. These pins would be controlled by an
output instruction preceding the MOVX.
In the second type of MOVX instruction, the Data Pointer generates a sixteen-bit address. P2
outputs the high-order eight address bits (the contents of DPH) while PO multiplexes the low-
order eight bits (DPL) with data. The P2 Special Function Register retains its previous con-
tents while the P2 output buffers are emitting the contents of DPH. This form is faster and
more efficient when accessing very large data arrays (up to 64K bytes), since no additional
instructions are needed to set up -.!he output ports.
It is possible in some situations to mix the two MOVX types. A large RAM array with its
high-order address lines driven by P2 can be addressed via the Data Pointer, or with code to
output high-order address bits to P2 followed by a MOVX instruction using RO or R I.
Example: An external 256 byte RAM using multiplexed addressldata lines is connected to
the 8051 Port O. Port 3 provides control lines for the external RAM. Ports 1
and 2 are used for normal 1/0. Registers 0 and 1 contain 12H and 34H. Loca-
tion 34H of the external RAM holds the value 56H. The instruction sequence,
MOVX A,@RI
MOVX @RO,A
copies the value 56H into both the Accumulator and external RAM location 12H.
February 1989 1-93

MOVX A,@Ri
Bytes:
Cycles: 2
Encoding: 11 1 1 0 o0 1 i
Operation: MOVX
(A) - «Ri»
MOVX A,@DPTR
Bytes:
Cycles: 2
Encoding: 11 1 1 0 0000
Operation: MOVX
(A) - «DPTR»
MOVX @RI,A
Bytes:
Cycles: 2
Encoding: 11 1 1 1 001
Operation: MOVX
«Ri» - (A)
MOVX @DPTR,A
Bytes:
Cycles: 2
Encoding: 11 1 1 1 0 0 0 0
Operation: MOVX
(DPTR)-(A)
February 1989 1-94

NOP
Function: No Operation
Description: Execution continues at the following instruction. Other than the PC, no registers or flags are
affected.
Example: It is desired to produce a low-going output pulse on bit 7 of Port 2 lasting exactly 5 cycles. A
simple SETB/CLR sequence would generate a one-cycle pulse, so four additional cycles must
be inserted. This may be done (assuming no interrupts are enabled) with the instruction
sequence,
CLR P2.7
NOP
NOP
NOP
NOP
SETB P2.7
Bytes:
Cycles:
Encoding: I0 0 0 0 I 0 0 0 0
Operation: NOP
(PC) +- (PC) +
MUL AB
Function: Multiply
Description: MUL AB multiplies the unsigned eight-bit integers in the Accumulator and register B. The
low-order byte of the sixteen-bit product is left in the Accumulator, and the high-order byte in
B. If the product is greater than 255 (OFFH) the overflow flag is set; otehrwise it is cleared.
The carry flag is always cleared.
Example: Originally the Accumulator holds the value 80 (SOH). Register B holds the value 160 (OAOH).
The instruction,
MUL AB
will give the product 12,800 (32ooH), so B is changed to 32H (oollooIOB) and the Accumula-
tor is cleared. The overflow flag is set, carry is cleared.
Bytes:
Cycles: 4
Encoding: I 1 0 1 0 0 1 0 0
Operation: MUL
(Ah_o +- (A) X (B)
(Bhs.8
February 1989 1-95

ORL <dest-byte> <src-byte>
Function: Logical-OR for byte variables

Description: ORL performs the bitwise logical-OR operation between the indicated variables, storing the
results in the destination byte. No flags are affected.
Example: If the Accumulator holds OC3H (! lOOOOIIB) and RO holds 55H (OIOIOIOIB) then the in-
struction,
ORL A,RO
will leave the Accumulator holding the value OD7H (lIOIOIIIB).
When the destination is a directly addressed byte, the instruction can set combinations of bits
in any RAM location or hardware register. The pattern of bits to be set is determined by a
mask byte, which may be either a constant data value in the instruction or a variable computed
in the Accumulator at run-time. The instruction,
ORL Pl,#OOIlOOIOB
will set bits 5, 4, and 1 of output Port 1.
ORL A,Rn
Bytes:
Cycles:
Encoding: I0 1 0 0 1 r r r
Operation: ORL
(A) - (A) V (Rn)
February 1989 1-96

ORL A,direct
Bytes: 2
Cycles:
Encoding: 10100 I0 10 1 I direct address
Operation: ORL
(A) +- (A) V (direct)
ORL A,@Ri
Bytes:
Cycles:
Encoding: 101 00 o1 1
Operation: ORL
(A) +- (A) V «Ri))
ORL A,#data
Bytes: 2
Cycles:
Encoding: I 0 1 0 0 I 0 1 oOl immediate data
Operation: ORL
(A) +- (A) V # data
ORL direct,A
Bytes: 2
Cycles:
Encoding: 10100 I 0 0 1 0 I direct address
Operation: ORL
(direct) +- (direct) V (A)
ORL direct, # data

Bytes: 3
Cycles: 2
immediate data
Encoding: 101 00 001 1 direct addr.
Operation: ORL
(direct) +- (direct) V # data
February 1989 1-97

ORL C, < src-blt >
Function: Logical-OR for bit variables

Description: Set the carry flag if the Boolean value is a logical I; leave the carry in its current state
otherwise. A slash ("I") preceding the operand in the assembly language indicates that the
logical complement of the. addressed bit is used as the source value, but the source bit itself is
not affected. No other flags are affected.
Example: Set the carry flag if and only if Pl.O = I, ACC. 7 = I, or OV = 0:
MOV C,Pl.O ;LOAD CARRY WITH INPUT PIN PIO
ORL C,ACC.7 ;OR CARRY WITH THE ACC. BIT 7
ORL C,IOV ;OR CARRY WITH THE INVERSE OF OV.
ORL C,blt
Bytes: 2
Cycles: 2
Encoding: 1 01 1 1 001 0 bitaddress I

Operation: ORL
(C) - (C) V (bit)
ORL C,/blt
Bytes: 2
Cycles: 2
Encoding: 11 0 1 0 1 0000 bitaddress I

Operation: ORL
(C) - (C) V (bit)
February 1989 1-98

Si 9 netics Microprocessor Prod ucts User's Guide
POP direct
Function: Pop from stack.

Description: The contents of the internal RAM location addressed by the Stack Pointer is read, and the
Stack Pointer is decremented by one. The value read is then transferred to the directly ad-
dressed byte indicated. No flags are affected.
Example: The Stack Pointer originally contains the value 32H, and internal RAM locations 30H
through 32H contain the values 20H, 23H, and OIH, respectively. The instruction sequence,
POP DPH
POP DPL
will leave the Stack Pointer equal to the value 30H and the Data Pointer set to 0123H. At this
point the instruction,
POP SP
will leave the Stack Pointer set to 20H. Note that in this special case the Stack Pointer was
decremented to 2FH before being loaded with the value popped (20H).
Bytes: 2
Cycles: 2
Encoding: LI _1__0_1-,-_0_0_0_0-, direct addr~
Operation: POP
(direct) - «SP))
(SP) - (SP) - I
PUSH direct
Function: Push onto stack

Description: The Stack Pointer is incremented by one. The contents of the indicated variable is then copied
into the internal RAM location addressed by the Stack Pointer. Otherwise no flags are affect-
ed.
Example: On entering an interrupt routine the Stack Pointer contains 09H. The Data Pointer holds the
value 0123H. The instruction sequence,
PUSH DPL
PUSH DPH
will leave the Stack Pointer set to OBH and store 23H and OIH in internal RAM locations
OAH and OBH, respectively.
Bytes: 2
Cycles: 2
Encoding: 1 1 1 ° ° ° °°
0 1 1
direct address
Operation: PUSH
(SP) - (SP) + I
«SP)) - (direct)
February 1989 1-99 "

RET
Function: Return from subroutine

Description: RET pops the high- and low-order bytes of the PC successively from the stack, decrementing
the Stack Pointer by two. Program execution continues at the resulting address, generally the
instruction immediately following an ACALL or LCALL. No flags are affected.
Example: The Stack Pointer originally contains the value OBH. Internal RAM locations OAH and OBH
contain the values 23H and OlH, respectively. The instruction,
RET
will leave the Stack Pointer equal to the value 09H. Program execution will continue at
location 0123H.
Bytes:
Cycles: 2
Encoding: 100100010
Operation: RET
(PCIS-S) +- «SP»
(SP) +- (SP) - 1
(PC7-O) +- «SP»
(SP) +- (SP) - 1
RETI
Function: Return from interrupt

Description: RETI pops the high- and low-order bytes of the PC successively from the stack, and restores
the interrupt logic to accept additional interrupts at the same priority level as the one just
processed. The Stack Pointer is left decremented by two. No other registers are affected; the
PSW is not automatically restored to its pre-interrupt status. Program execution continues at
the resulting address, which is generally the instruction immediately after the point at which
the interrupt request was detected. If a lower- or same-level interrupt had been pending when
the RETI instruction is executed, that one instruction will be executed before the pending
interrupt is processed.
Example: The Stack Pointer originally contains the value OBH. An interrupt was detected during the
instruction ending at location 0122H. Internal RAM locations OAH and OBH contain the
values 23H and OlH, respectively. The instruction,
RETI
will leave the Stack Pointer equal to 09H and return program execution to location 0123H.
Bytes:
Cycles: 2
Encoding: .... _ _-'-0_0_1_0--,

1_0_0
Operation: RETI
(PCIS-S) +- «SP»
(SP)- (SP) - 1
(PC7-O) +- «SP»
(SP) +- (SP) - 1
February 1989 1-100

RL A
Function: Rotate Accumulator Left

Description: The eight bits in the Accumulator are rotated one bit to the left. Bit 7 is rotated into the bit 0
position. No flags are affected.
Example: The Accumulator holds the value OC5H (llOOOIOIB). The instruction.
RL A
leaves the Accumulator holding the value 8BH (lOOOIOIIB) with the carry unaffected.
Bytes:
Cycles:
Encoding: 1 0 0 1 0 0 0 1 1
Operation: RL
CAn+l)_CAn). n = 0 - 6
CAO)-CA7)
RLC A
Function: Rotate Accumulator Left through the Carry flag

Description: The eight bits in the Accumulator and the carry flag are together rotated one bit to the left. Bit
7 moves into the carry flag; the original state of the carry flag moves into the bit 0 position. No
other flags are affected.
Example: The Accumulator holds the value OC5H (lIOOOIOIB). and the carry is zero. The instruction.
RLC A
leaves the Accumulator holding the value 8BH (IOOOIOIOB) with the carry set.
Bytes:
Cycles:
Encoding: 1-1 _0_0_1_-,-_0_0_1_1-.1
Operation: RLC
CAn+l)~(An). n - 0 - 6
CAO)-CC)
CC)-CA7)
February 1989 1-101

RR A
Function: Rotate Accumulator Right

Description: The eight bits in the Accumulator are rotated one bit to the right. Bit 0 is rotated into the bit 7
position. No flags are affected.
Example: The Accumulator holds the value OCSH (I 1000 101 B). The instruction.
RR A
leaves the Accumulator holding the value OE2H (llIOOOIOB) with the carry unaffected.
Bytes:
Cycles:
Encoding: 1000010011
Operation: RR
(An) _(An+l). n = 0 - 6
(A7)-(AO)
RRC A
Function: Rotate Accumulator Right through Carry flag

Description: The eight bits in the Accumulator and the carry flag are together rotated one bit to the right.
Bit 0 moves into the carry flag; the original value of the carry flag moves into the bit 7
position. No other flags are affected.
Example: The Accumulator holds the value OCSH (1 100010 1B). the carry is zero. The instruction.
RRC A
leaves the Accumulator holding the value 62 (0 llOOO lOB) with the carry set.
Bytes:
Cycles:
Encoding: 100010011
Operation: RRC
(An) - (An+l). n - 0 - 6
(A7) - (C)
(C)- (AO)
February 1989 1-102

SETB <bit>
Function: Set Bit

Description: SETB sets the indicated bit to one. SETB can operate on the carry flag or any directly
addressable bit. No other flags are affected.
Example: The carry flag is cleared. Output Port 1 has been written with the value 34H (001 101OOB). The
instructions,
SETB C
SETB Pl.O
will leave the carry flag set to 1 and change the data output on Port 1 to 35H (001lO101B).
SETB C
Bytes:
Cycles:
Encoding: I1 10 1 001 1
Operation: SETB
(C)-l
SETB bit
Bytes: 2
Cycles:
Encoding: 11 1 0 1 001 0 bit address
Operation: SETB
(bit) - 1
February 1989 1-103

SJMP rei
Function: Short Jump

Description: Program control branches unconditionally to the address indicated. The branch destination is
computed by adding the signed displacement in the second instruction byte to the PC, after
incrementing the PC twice. Therefore, the range of destinations allowed is from 128 bytes
preceding this instruction to 127 bytes following it.
Example: The label "RELADR" is assigned to an instruction at program memory location 0123H. The
instruction,
SJMP RELADR
will assemble into location OIOOH. After the instruction is executed, the PC will contain the
value 0123H.
(Note: Under the above conditions the instruction following SJMP will be at 102H. Therefore,
the displacement byte of the instruction will be the relative offset (0123H-0102H) = 21H. Put
another way, an SJMP with a displacement of OFEH would be a one-instruction infinite loop.)
Bytes: 2
Cycles: 2
Encoding: I10 0 0 0 0 0 0 I reI. address

Operation: SJMP
(PC) +- (PC) + 2
(PC) +- (PC) + rei
February 1989 1-104

SUBB A,<src-byte>
Function: Subtract with borrow

Description: SUBB subtracts the indicated variable and the carry flag together from the Accumulator,
leaving the result in the Accumulator. SUBB sets the carry (borrow) flag if a borrow is needed
for bit 7, and clears C otherwise. (If C was set before executing a SUBB instruction, this
indicates that a borrow was needed for the previous step in a multiple precision subtraction, so
the carry is subtracted from the Accumulator along with the source operand.) AC is set if a
borrow is needed for bit 3, and cleared otherwise. OV is set if a borrow is needed into bit 6, but
not into bit 7, or into bit 7, but not bit 6.
When subtracting signed integers OV indicates a negative number produced when a negative
value is subtracted from a positive value, or a positive result when a positive number is
subtracted from a negative number.
The source operand allows four addressing modes: register, direct, register-indirect, or imme-
diate.
Example: The Accumulator holds OC9H (llOOIOOlB), register 2 holds 54H (OIOlOlOOB), and the carry
flag is set. The instruction,
SUBB A.R2
will leave the value 74H (01 110100B) in the accumulator, with the carry flag and AC cleared
but OV set.
Notice that OC9H minus 54H is 75H. The difference between this and the above result is due
to the carry (borrow) flag being set before the operation. If the state of the carry is not known
before starting a single or multiple-precision subtraction, it should be explicitly cleared by a'
CLR C instruction. .
SUBB A,Rn
Bytes:
Cycles:
Encoding: 1 r r r
Operation: SUBB
(A) -- (A) - (C) - (Rn)
February 1989 1-105

SUBB A,dlrect
Bytes: 2
C'ycles:
Encoding: ,. 1 0 0 1 0 1 0 1 direct address
Operation: SUBB
(A) . - (A) - (C) - (direct)
SUBB A,@RI
Bytes:
Cycles:
Encoding: I1 0 0 1 0 1 1
Operation: SUBB
(A) . - (A) - (C) - «Ri»
SUBB A,#data
Bytes: 2
Cycles:
Encoding: I10 0 1 0 1 0 0 immediate data
Operation: SUBB
(A) . - (A) - (C) - #data
SWAP A
Function: Swap nibbles within the Accumulator

Description: SWAP A interchanges the low- and high-order nibbles (four-bit fields) of the Accumulator
(bits 3-0 and bits 7-4). The operation can also be thought of as a four-bit rotate instruction. No
flags are affected.
Example: The Accumulator holds the value OC5H (lIOOOIOIB). The instruction,
SWAP A
leaves the Accumulator holding the value 5CH (0101 I IOOB).

Bytes:
Cycles:
Encoding: I1 10 0 0 1 0 0
Operation: SWAP
(A3-0) -;:: (A7-4)
February 1989 1-106

XCH A,<byte>
Function: Exchange Accumulator with byte variable

Description: XCH loads the Accumulator with the contents of the indicated variable, at the same time
writing the original Accumulator contents to the indicated variable. The source/destination
operand can use register, direct, or register-indirect addressing.
Example: RO contains the address 20H. The Accumulator holds the value 3FH (OOllllllB). Internal
RAM location 20H holds the value TSH (01110101B). The instruction,
XCH A,@RO
will leave RAM location 20H holding the values 3FH (OOI11111B) and 75H (0111010lB) in
the accumulator.
XCH A,Rn
Byte.:
Cycle.:
Encoding: 11 100 r r r I
Operation: XCH
(A) ~ (Rn)
XCH A,dlrect
Byte.: 2
Cycle.:
Encoding: 11 100 o1 0 1 direct address
Operation: XCH
(A) ~ (direct)
XCH A,@RI
Byte.:
Cycle.:
Encoding: 11 100 o1 1 i
Operation: XCH
(A) ~ «Ri»
February 1989 1-107

XCHD A,@RI
Function: Exchange Digit

DescriptIon: XCHD exchanges the low-order nibble of the Accumulator (bits 3-0), generally representing a
hexadecimal or BCD digit, with that of the internal RAM location indirectly addressed by the
specified register. The high-order nibbles (bits 7-4) of each register are not affected. No flags
are affected.
Example: RO contains the address 2OH. The Accumulator holds the value 36H (00 11 0 110B). Internal
RAM location 20H holds the value 75H (OIIIOIOIB). The instruction,
XCHD A,@RO
will leave RAM location 20H holding the value 76H (011101 lOB) and 35H (00110101B) in the
Accumulator.
Bytes:
Cycles:
EncodIng: 11101011
OperatIon: XCHD
(A3-O) -;. «Ri3-O»
XRL < dest-byte >, <src-byte >
FunctIon: Logical Exclusive-OR for byte variables

DescrIptIon: XRL performs the bitwise logical Exclusive-OR operation between the indicated variables,
storing the results in the destination. No flags are affected.
(Note: When this instruction is used to modify an output port, the value used as the original
port data will be read from the output data latch, not the input pins.)
Example: If the Accumulator holds OC3H (11000011B) and register 0 holds OAAH (10101OIOB) then
the instruction,
XRL A,RO
will leave the Accumulator holding the value 69H (01101001B).
When the destination is a directly addressed byte, this instruction can complement combina-
tions of bits in any RAM location or hardware register. The pattern of bits to be complement-
ed is then determined by a mask byte, either a constant contained in the instruction or a
variable computed in the Accumulator at run-time. The instruction,
XRL Pl,#00110001B
will complement bits 5, 4, and 0 of output Port 1.
February 1989 1-108

XRL A,Rn
Bytes:
Cycles:
Encoding: I0 1 1 0 1 r r r
Operation: XRL
(A) +- (A) ¥ (Rn)
XRL A,direct
Bytes: 2
Cycles:
Encoding: I0 1 1 0 o1 0 1 direct address
Operation: XRL
(A) +- (A) ¥ (direct)
XRL A,@RI
Bytes:
Cycles:
Encoding: 1 01 1 0 o1 1 i
Operation: XRL
(A) +- (A) ¥ «Ri»
XRL A,#data
Bytes: 2
Cycles:
Encoding:
1 01 1 0 o10 0 immediate data
Operation: XRL
(A) +- (A) ¥ #data
XRL dlrect,A
Bytes: 2
Cycles:
Encoding: 1 01 1 0 001 0 direct address
Operation: XRL
(direct) +- (direct) ¥ (A)
February 1989 1-109

User's Guide
XRL dlrect,#dMa
Bytes: 3
Cycles: 2
Encoding: I 0 1 1 0 I 0 0 1 1 I I direct address I I immediate data I

Operation: XRL
(direct) +- (direct) ¥ #data
February 1989 1-110

Section 1 8051 Family EPROM Products
To program the SC87C51, SC87C451, or SC87C552, the

EPROM PRODUCTS address of the EPROM location to be programmed is
All 80C51 derivative products offered by Signetics are applied to ports 1 and 2 as shown in Figure 59. The f·
supported with an EPROM version. Currently available code byte to be programmed into this location is applied
EPROM parts are the 87C51, 87C451, and the 87C751. to port O. RST, PSEN and the pins of ports 2 and 3
EPROM versions of the 83C552, 83C652, and 83C752 specified in Table 20 are held at the "Program Code
are now in development. Data" levels specified in the table. The ALE/PROG is
then pulsed low 25 times to program the addressed loca-
All EPROM products are available in both windowed tion.
DIP and OTP package configurations. The windowed
DIP package allows the EPROM to be erased under a ENCRYPTION TABLE
strong UV light source making program development
easier and faster. The OTP (One Time Programmable) The encryption table is a feature of the SC87C51, and
version cannot be erased because there is no window its derivatives, that protects the code from being easily
through which the die could be exposed to UV light. read by anyone other than the programmer. The encryp-
While the EPROM can only be programmed once in the tion table is 16 bytes of code that are exclusive NORed
OTP package, the part costs less than in windowed DIP with the program code data as it is read out. The first
and therefore offers an advantage for those not desiring byte is XNORed with the first location read, the second
to use the masked ROM version of the part. with the second read, etc. through the sixteenth byte
read. The seventeenth byte is XNORed with the first byte
The EPROM products are fully supported on the industry of the encryption table, the eighteenth with the second,
standard EPROM programmers. etc. and on in sixteen byte groups.
PROGRAMMING THE 87C51, 87C451 AND 87C552 After the Encryption table has been programmed the us-
er has to know its contents in order to correctly decode
The setup for programming the microcontroller is shown the program code data. The encryption table itself can-
in Figure 59. Note that the part is running with a 4 to 6 not be read out.
MHz oscillator. The clock must be running because the
device is executing internal address and program data The encryption table is programmed in the same manner
transfers during the programming. as the program memory, but using the "Pgm Encryption
Table" levels specified in Table 20. After the encryption
table is programmed verification cycles will produce only
encrypted information.
+5V
Vee
IA
A 0-A7 P1 PO PGM DATA
1 RST EA/vpp +12.75V
25 100us PULSES
1 P3.6 ALE/P"ROO TO GROUND
P3.7 SC87C51
1 PsEN
XTAL2 P2.7
4-6MHz ~ =~
~
P2.6
T T XTAL1
P2.0
IA
-P2.3 I ~
A8-A11
~ Vss
- ,--
Figure 59. Programming Configuration
February 1989 1-111

Table 20. EPROM Programming Modes

MODE RST PSEN ALE/PROG EA/Vpp P2.7 P2.6 P3.7 P3.6
Read signature 1 0 1 1 0 0 0 0
Program code data 1 0 O· Vpp 1 0 1 1
Verify code data 1 0 1 1 0 0 1 1
Pgm encryption table 1 0 O· Vpp 1 0 1 0
Pgm lock bit 1 1 0 O· Vpp 1 1 1 1
Pgm lock bit 2 1 0 o· Vpp 1 1 0 0
NOTES:
1. "0" = valid low for that pin, "1" = valid high for that pin.
2. Vpp = 12.7SV ±O.2SV.
3. Vee = 5V ±10% during programming and verification.
"ALE/PROG receives 25 programming pulses while Vpp is held at 12.75V. Each programming pulse is low for lOOI1S
(±101lS) and high for a minimum of lOllS.
LOCK BIT PROGRAM VERIFICATION
There are two lock bits on the SC87C51 that, when set, If lock bit 2 has not been programmed the on-chip pro-
prevent the program data memory from being read out gram memory can be read out for program verification.
or programmed further. To program the lock bits repeat To verify the contents of the program memory, the ad-
the programming sequence using the "Pgm Lock Bit" dress of the location to be read is applied to ports 1 and
levels specified in Table 20. 2 as shown in Figure 60. The other pins are held at the
"Verify Code Data" levels indicated in Table 20. The
After the first lock bit is programmed, further program- contents of the addressed location will appear on port O.
ming of the code memory or the encryption table is dis- For this operation external pull-ups are required on port
abled. The other lock bit can of course still be pro- o as shown in figure 60. Note that if the encryption table
grammed. With only lock bit one programmed, the has been programmed the data presented at port 0 will
memory can still be read out for program verification. be the exclusive NOR of the program byte with a byte
After the second lock bit is programmed, it is no longer from the encryption table.
possible to read out (verify) the program memory.
+5V
Vee
AO-A7 - - - - , I I Pl P0l-_~'; PGM DATA
----oI RST EA/vpp I t - - - -
- _ _--oj P3.6 ALE/PROG I t - - - -
_ _ _........ P3.7 SC87C51

PSEN 1"---- 0
r--_._--I XTAL2 P2.7 10----- 0 (ENABLE)
P2.6 I t - - - - 0
P2.0 11'---- AS-All

-P2.3,v----
'---......-+-1 XTAL 1
Vss
Figure 60. Program Verification
February 1989 1-112

SIGNATURE BYTES The Xl pin is the oscillator input and receives the mas-
ter system clock. This clock should be between 1.2 and
The SC87C51 contains two signature bytes that can be 6MHz.
read and used by an EPROM programming system to
identifY the device. The signature bytes identifY the de- The RESET pin is used to accept the serial data stream
vice as an SC87C51 manufactured by Signetics . that places the 87C75l into various programming modes.
This pattern consists of a 10-bit code with the LSB sent
The signature bytes are read by the same procedure as a first. Each bit is synchronized to the clock input Xl.
normal verification of locations 030H and 031H, except
that P3.6 and P3.7 need to be pulled to a logic low. The To program the 87C7Sl the part must be put into the
values are: programming mode by presenting the proper serial code
(see Table 21) to the RESET pin. To do this RESET
(030H) = ISH indicates the part made by Signetics should be held high for at least two machine cycles. Port
(031H) = 90H 87C451 94H 87C552 pins PO.l and PO.2 will be at VOH as a result of this,
9lH 87C751 95H 87C752 but they must be driven high prior to sending the serial
92H 87C51 96H 87C550 data stream on the RESET pin. The serial data bits can
93H 87C652 97H 87C52 now be transmitted over the RESET pin placing the
87C75l into one of the programming modes. Following
EPROM ERASURE the transmission of the last data bit the reset pin should
be held low.
Erasure of the EPROM occurs when the chip is exposed
to light with wavelengths shorter than 4000 angstroms. Next the address information for the location to be pro-
Sunlight and fluorescent lighting have wavelengths in this grammed is placed on Port 3 and ASEL is used to per-
range, so exposure to these light sources over an ex- form the address mUltiplexing. ASEL should be driven
tended period of time (about I week in sunlight, or 3 high and then Port 3 driven with the high order address
years in room level fluorescent lighting) could cause in- bits. ASEL is then driven low latching the high order
advertent erasure. It is recommended, for this reason, bits internally. Port 3 can now be driven with the low 8
that an opaque label be placed over the window. If the bits of the address, completing the addressing of the lo-
part is Subject to elevated temperatures or an environment cation to be programmed.
where solvents are used, Kapton tape (Fluorglas part number
2345-5 or its equivalent) can be used. A high voltage Vpp level is now applied to the Vpp in-
put. This sets Port 1 as an input port. The data to be
The recommended erasure procedure is to expose the programmed to the EPROM array should be placed on
chip to ultraviolet light (at 2537 angstroms) to an inte- Port 1. A series of 25 programming pulses is now ap-
grated dose of at least 15W-sec/cm2. Exposing the plied to the PGM pin (PO.l) to program the addressed
EPROM to an ultraviolet lamp of 12,OOOJ.LW/cm2 rating EPROM location.
for 20 to 40 minutes, at a distance of I inch, is ade-
quate. PROGRAM VERIFICATION
PROGRAMMING THE 87C751 AND 87C752 The EPROM array can be verified by placing the part in
the programming mode as described above and forcing
The 87C751 and 87C752 are programmed using a Quick- the Vpp pin to the VOH level. Four machine cycles after
pulse programming algorithm that is similar to that used addressing a location the contents of the addressed loca-
for the 87C51. It differs from the 87CSl in that a serial tion will appear on Port 1.
data stream is used to place the 87C751 in the pro-
gramming mode. 87C751 AND 87C752 SIGNATURE BYTES
Figure 61 shows a block diagram of the programming The signature bytes for the 87C75l and 87C752 are read
configuration for the 87C751. Port pin PO.2 is used for differently and are in different locations than those on
the programming voltage supply input (Vpp signal). Port the 87C51. Due to its reduced pin count, the part has to
pin PO.I is used for the program (PGM) signal. be put into "Signature Byte Read Mode" by placing a 10-
bit serial data stream on the Reset pin. The proper code
Port 3 accepts the address input for the EPROM loca- and the conditions of PO.l and PO.2, for this mode, are
tion to be programmed. Both the high and low compo- shown in Table 21.
nents of the eleven bit address are presented to the part
through port 3. Multiplexing of the address components Once the part has been placed into the Signature Byte
is performed using ASEL (PO.O). Read Mode, the signature bytes can be read by the same
procedure as a normal verification of locations OlEH
Port 1 is used as a bidirectional data bus during pro- and OlFH. The values are:
gramming and verifY operations. During the program-
ming mode, it accepts the byte to be programmed. In OlEH = ISH indicates the part was made by Signetics
the verifY mode, it returns the contents of the specified OlFH = 9lH - 87C751
address location. 01FH = 95H - 87C752
February 1989 1-113

PROGRAMMING FEATURES
The 87C7S1 has all of the special programming features

incorporated within its EPROM array that the 87CSI
has. It has an encryption key table and two security bits
(lock bits). These function exactly as they do in the
87CS1. They are programmed or verified by sending the
proper code over the RESET pin (see table 21) and then
following the 87C7S1 programming procedure as de-
scribed previously.
ERASURE CHARACTERISTICS
The erasure procedure is exactly the same as that de-

scribed for the 87CS1.
Table 21. Implementing ProgramlVerify Modes
Operation Serial Code PO.l (pGMI) PO.2 (Vpp)

Program user EPROM 296H -* Vpp
Verify user EPROM 296H VIH VIH
Program key EPROM 292H -* Vpp
Verify key EPROM
Program security bit 1
292H
29AH -.-.
VIH VIH
Vpp
Vpp
Program security bit 2 298H
Verify security bits 29AH VIH VIH
Read siJl;nature bytes 19CH VIH VIH
NOTE.
*Pulsed from V IH to V 1L and returned to VIII'
87C751
Vee _ + l I V
AO-A7/AB-AIO PJ.O-PJ.7
Vss
~
ADDRESS S11IOBE PO.O/ASEL
PI.D-Pl.7 DATA BUS
PROGRAMMING
PULSES PO.I
Vpp/VIH ~~ PO.2
CLK SOURCE XTALI
Y RESET
CONTROL
LOGIC
I
I
RESET
February 1989 1-114

Signetics SCN8031 AH/SCN8051 AH
Single-Chip 8-Bit Microcontroller
Product Specification
Microprocessor Division
DESCRIPTION FEATURES PIN CONFIGURATION

The Signetics SCN8031AH/SCN8051AH • Reduced supply current
is a high-performance microcontroller • 4K X 8 ROM (SCN8051AH)
fabricated using the Signetics highly reli- .128 X 8 RAM P1.0 ~ 40 Vee
able +5V, depletion-load, N-channel, sill-
• Four 8-bit ports, 32 I/O lines P1.1 4 ~ PO.O/ADO
con-gate, N500 MOS process technol-
• Two 16-bit timerlevent P1.2~ ~ PO.1/AD1
ogy. It provides the hardware features,
architectural enhancements and instruc- counters P1.3~ ~ PO.2/AD2
tions that are necessary to make it a • High-performance full-duplex P1.4~ ~ PO.3/AD3

powerful and cost-effective controller for serial channel P1.5~ ~ PO.4/AD4
applications requiring up to 64K bytes of
program memory and/or up to 64K bytes
• External memory expandable to P1. 6 .r. ~ PO.5/AD5
128K P1.7 ~ ~ PO.6/AD6
of data storage. • Boolean processor RST 9 ~ ~7/AD7
The SCN8051AH contains a 4K X 8
• Industry standard 8051 RXD/P3.0~ DIP ~ EA
read-only program memory, a 128 X 8 architecture: ~P3.1~ 30 ALE
read/write data memory, 32 I/O lines, Non-paged jumps ~/P3.2~ ~PSEN
two 16-bit timer/counters, a five-50urce - Direct addressing INT1/P3.3~ ~ P2.7/A15
two-priority-level nested interrupt struc- - Four 8-register banks
TO/P3.4~ ~ P2.6/A14
ture, a serial I/O port for either multi-
processor communications, I/O expan-
- Stack depth up to U8-bytes
- Multiply, divide, subtract,
.!!./P3.5~ g P2.5/A13
sion, or full-duplex UART, and on-chip ~/P3.6~ ~ P2.4/A12
compare
oscillator and clock circuits. The SCN- RD/P3.7jolJ ~ P2.3/A11
• Most instructions execute
8031 AH is identical, except that it lacks
in 1!lS
XTAL2~ g P2.2/A10
the program memory. For systems that XTAL1~ ~ P2.1/A9
require extra capability, the SCN8051AH
• 4!lS multiply and divide
Vss.gfl ~ P2.0/A8
can be expanded using standard TTL
compatible memories and byte oriented TOP VIEW
peripheral controllers. INDEX
LOGIC SYMBOL CORNER 6 1 40
8
The SCN8051AH microcontroller, like its
SCN8048 predecessor, is efficient both
as a controller and as an arithmetic PLCC
processor. It has extensive facilities for
binary and BCD arithmetic and excels in 17 29
bit-handling capabilities. Efficient use of
program memory results from an instruc- 18 28
tion set consisting of 44% one-byte, TOP VIEW
41 % two-byte, and 15% three-byte in- Pin FunctionPin Function
structions. With a 12MHz crystal, 58% 1 NC 23 NC
of the instructions execute in 1JIS, 40% 2 P1.0 24 P2.0/A8
3 P1.1 25 P2.1/A9
in 2j1S and multiply and divide require on- 4 P1.2 26 P2.2/A10
ly 4j1S. 5 P1.3 27 P2.3/A11
6 P1.4 28 P2.4/A12
7 P1.5 29 P2.5/A13
8 P1.6 30 P2.6/A14
9 P1.7 31 P2.7/A15
10 RST 32 i>sEN
11 RxD/P3.033 ALE
12 NC 34 NC
13 TxD/P3.135 EA
14 1m'ii/P3.2
36 PO.7/AD7
15 iiili'i/P3.3
37 PO.6/AD6
16 TO/P3.4 38 PO.5/AD5
17 T1/P3.5 39 PO.4/AD4
18 WR/P3.6 40 PO.3/AD3
19 RD/P3.7 41 PO.2/AD2
20 XTAL2 42 PO.1/AD1
21 XTAL1 43 PO.O/ADO
22 Vss 44 Vee
February 1989 1-115 853-0096 85292H

Signetics Microprocessor Products Product Specification
Single-Chip 8-Bit Microcontroller SCN8031 AH /SCN8051 AH
ORDERING INFORMATION
PART NUMBER SELECTION
Temperature and
ROMless ROM Frequency
ROM~R:~]e:)HCJCJCJCJ1CJ :I:X:
Package
SCN8031 HACN40 SCNS051 HACN40 -40 to +S5°C plastic DIP 3.5 to 12MHz
ROM Pattern No.
31 - Extl12S Applies to masked ROM versions SCNS031 HCCN40 SCN8051 HCCN40 o to +70°C plastic DIP 3.5 to 12MHz
51 - 4K/12S only. Number will be assigned by
Signetics. Contact Signetics sales SCNS031 HCFN40 SCNS051 HCFN40 o to +70 0 C plastic DIP 3.5 to 15MHz
Power office for ROM pattern submission SCN8031 HAFN40 SCNS051 HAFN40 3.5 to 15MHz
-40 to +S5°C plastic DIP
Consumption requirements.
H -P~~~~c:~ Pins
SCNS031 HCCA44 SCNS051 HCCA44 o to + 70°C plastic PLCC 3.5 to 12MHz
40 = 40-pin SCNS031 HACA44 SCN8051 HACA44 -40 to +S5°C plastic PLCC 3.5 to 12MHz
44 - 44-pin
SCNS031 HCFA44 SCNS051 HCFA44 o to + 70°C plastic PLCC 3.5 to 15MHz
Package
A - Plastic LCC SCNS031 HAFA44 SCN8051 HAFA44 -40 to +S5°C plastic PLCC 3.5 to 15MHz
I - Ceramic DIP
N - Plastic DIP
Speed
C - 3.5 to 12MHz
F - 3.5 to 15MHz
Operating Temperature Range
A - -40°C to +S5°C
C = OOC to +70 0 C
BLOCK DIAGRAM
PO.o-PO.7 P2.D-P2.7
- - - - - - - - - - ~:-S':l"" --------1
peON SCON TMOD TCON

THO TLO THI
TLI
SBUF IE IP
PsEN
ALE
EA
RST
I
I
)
Pl.0-Pl.7 P3.o-PJ.7
February 1989 1-116

Single-Chip 8-Bit Microcontroller SCN8031AH/SCN8051AH
PIN DESCRIPTION
PIN NO.
MNEMONIC f--~---1 TYPE NAME AND FUNCTION
DIP LCC
Vss 20 22 I Ground: OV reference.
40 44 I Power Supply: This is the power supply voltage for normal, idle, and power-down op-
Vee
eration.
PO.O-PO'? 39-32 43-36 I/O Port 0: Port 0 is an open-drain, bidirectional I/O port. Port 0 pins that have Is written
to them float and can be used as high-impedance inputs. Port 0 is also the multiplexed
low-order address and data bus during accesses to external program and data mem-
ory. In this application, it uses strong internal pullups when emitting Is.
Pl.0-Pl.? 1-8 2-9 I/O Port 1: Port 1 is an 8-bit bidirectional I/O port with internal pull-ups. Port 1 pins that
have Is written to them are pulled high by the internal pull ups and can be used as
inputs. As inputs, port 1 pins that are externally pulled low will source current because
of the internal pUll-Ups. (See DC Electrical Characteristics: lid·
P2.0-P2.? 21-28 24-31 I/O Port 2: Port 2 is an 8-bit bidirectional I/O port with internal pUll-Ups. Port 2 pins that
have 1s written to them are pulled high by the internal pullups and can be used as
inputs. As inputs, port 2 pins that are externally being pulled low will source current
because of the internal pullups. (See DC Electrical Characteristics: lid. Port 2 emits the
high-order address byte during fetches from external program memory and during
accesses to external data memory that use 16-bit addresses (MOVX @DPTR). In this
application, it uses strong internal pull-ups when emitting Is. During accesses to
external data memory that use 8-bit addresses (MOVX @Ri), port 2 emits the
contents of the P2 special function register.
P3.0-P3.7 10-17 11, I/O Port 3: Port 3 is an 8-bit bidirectional I/O port with internal pullups. Port 3 pins that
13-19 have 1s written to them are pulled high by the internal pullups and can be used as
because of the pUll-Ups. (See DC Electrical Characteristics: lid. Port 3 is also used for
the special features listed below:
10 11 I RxD (P3.0): Serial input port
11 13 o TxD (P3.1): Serial output port
12 14 I INTO (P3.2): External interrupt
13 15 I INT1 (P3.3): External interrupt
14 16 I TO (P3.4): Timer 0 external input
15 17 I I!JP3.5): Timer 1 external input
16 18 o WR (P3.6): External data memory write strobe
17 19 o RD (P3. 7): External data memory read strobe
RST 9 10 I Reset: A high on this pin for two machine cycles while the oscillator is running, resets
the device. An internal diffused resistor to Vss permits a power-on reset using only an
external capacitor to Vee.
ALE 30 33 I/O Address Latch Enable: Output pulse for latching the low byte of the address during an
access to external memory. In normal operation, ALE is emitted at a constant rate of
1/6 the oscillator frequency, and can be used for external timing or clocking. Note that
one ALE pulse is skipped_during each access to external data memory.
29 32 o Program Store Enable: The read strobe to external program memory. When the device
is executing code from externl!L..!2!2gram memory, PSEN is activated twice each
machine cycle, except that two PSEN activations are skipped during each access to
external data memory. PSEN is not activated during fetches from internal program
memory.
31 35 I External Access Enable: EA must be externally held low to enable the device to fetch
code from external program memory locations OOOOH and OFFFH. If EA is held high, the
device executes from internal program memory unless the program counter contains an
address greater than OFFFH.
XTALI 19 21 I Crystal 1: Input to the inverting oscillator amplifier.
XTAL2 18 20 o Crystal 2: Output from the inverting oscillator amplifier and input to the internal clock
generator circuits.
February 1989 1-117

Single-Chip 8-Bit Microcontroller SCN8031 AH/SCN8051 AH

OSCILLATOR CHARACTERISTICS To drive the device from an external DESIGN CONSIDERATIONS
XTAL1 and XTAL2 are the input and out- clock source, XTAL2 should be driven At powero{)n, the voltage on Vec and
put, respectively, of an Inverting ampli- while XTAL1 is left unconnected. There RST should come up at the same time
fier. The pins can be configured for use are no requirements on the duty cycle of for a proper start-up.
as an on-chip oscillator, as shown in the the external clock signal, because the
logic symbol, page 1. input to the internal clock circuitry is
through a divide.oy-two flip-flop. How-
ever, minimum and maximum high and
low times specified in the data sheet
must be observed.
ABSOLUTE MAXIMUM RATINGS1, 2, 3

PARAMETER RATING UNIT
Storage temperature range -65 to +150 °C
All voltages with respect to ground -0.5 to +7.0 V
Power dissipation 1.0 W
DC ELECTRICAL CHARACTERISTICS TA - O°C to +70°C, Vec - 4.5 to S.5V, Vss - OV4, 5

Limits
Symbol Parameter Test Conditions Unit
Min Max
VIL Input low voltage -0.5 0.8 V
VIH Input high voltage, except RST and XTAL2 2 Vcc+0.5 V
VIHl Input high voltage to RST for reset, XTAL2 XTAL1 to Vss 2.5 Vcc+0.5 V
VOL Output low voltage, ports 1, 2, 36 IOL - 1.6mA 0.45 V
VOLl Output low voltage, port 0, ALE, PSEN6 IOL - 3.2mA 0.45 V
VOH Output high voltage, ports 1, 2, 3 IOH - -80IJA 2.4 V

VOHl Output high voltage port 0, ALE, PSEN)3 IOH - -400IJA 2.4 V
IlL Logical 0 Input current, ports 1, 2, 3 VIN - 0.45V -500 IJA
IIHl Input high curent to RST for reset VIN < Vcc - 1.5V 500 IJA
ILl I nput leakage current, port 0, EA 0.45 < VIN < Vcc ±10 IJA
IIL2 Logical 0 input current for XTAL2 XTAL1 - Vss, VIN - 0.4SV -3.2 mA
Icc Power supply current: All outputs disconnected 125 mA
and EA - Vcc
CIO Pin capacitance 10 pF
TA = -40"C to +85"C - Extended temperature range - SCN8051HAC only
VIH Input high voltage, except RST and XTAL2 2.2 Vcc+O•S V
VIHl Input high voltage to RST for reset, XTAL2 XTAL1 to Vss 2.7 V
Icc Power supply current: All outputs disconnected 175 mA
and EA - Vcc
NOTES:
1. Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only and
functional operation of the device at these or any conditions other than those described in the AC and DC Electrical Characteristics sec-
tion of this specification is not implied.
2 For operating at elevated temperatures, the device must be derated based on +l50o C maximum junction temperature.
3. This product includes circuitry specifically designed for the protection of its internal devices from the damaging effects of excessive static
charge. Nonetheless, it Is suggested that conventional precautions be taken to avoid applying voltages greater than the rated maxima.
4. Parameters are valid over operating temperature range unless otherwise specified.
5. All voltage measurements are referenced to ground. For testing, all Input signals swing between O.45V and 2.4V with a transition time of
20ns maximum. All time measurements ·are referenced at Input voltages of O.BV and 2.0V and at output voltages of O.BV and 2.0V as
appropriate.
6. VOL is degraded when the device rapidly discharges external capaCitance. This AC noise is most pronounced during emission of address
data. When using external memory, locate the latch or buffer as close to the device as possible.
Emitting Degraded
Datum Ports VO Lines VOL (Peak Max)
Address P2, PO Pl, P3 O.BV
Write Data PO Pl, P3, ALE O.BV
7. CL - 100pF for port 0, ALE and J5Sm outputs; CL - BOpF for all other ports.
February 1989 1-118


AC ELECTRICAL CHARACTERISTICS TA - O°C to +70°C or -40°C to +85°C, VCC - 5V ±20%, Vss - OV1, 2
12MHz CLOCK VARIABLE CLOCK
SYMBOL FIGURE PARAMETER
Min Max Min Max
I UNIT
Program Memol'll
1/tCLCL 1 Oscillator frequency: Speed Versions
SCN8051 C 3.5 12 MHz
SCN8051 F 3.5 15 MHz
tLHLL 1 ALE pulse width 127 2tCLCL 40 ns
tAVLL 1 Address valid to ALE low 43 tCLCL-40 ns
tLLAX 1 Address hold after ALE low 48 tCLCL -35 ns
tLLlV 1 ALE low to valid instruction in 233 4tCLCL 100 ns
tLLPL 1 ALE low to PSEN low 58 tCLCL -25 ns
tp PH 1 PSEN pulse width 215 3tCLCL-35 ns
tpLiV 1 PSEN low to valid instruction in 125 3tCLcL -125 ns
tpXIX 1 Input instruction hold after PSEN 0 0 ns
IpXIZ 1 Input instruction float after PSEN 63 tCLCL -20 ns
tAVIV 1 Address to valid instruction in 302 5tCLCL-115 ns
tpLAZ 1 PSEN low to address float 20 20 ns
tpXAV 1 PSEN to address valid 75 tCLCL-8 ns
Data Memory
tRLRH 2, 3 RD pulse width 400 6tCLCL-100 ns
tWLWH 2,3 WR pulse width 400 6tCLcL -100 ns
tRLDV 2, 3 RD low to valid data in 252 5tcLcL-165 ns
tRHDX 2, 3 Data hold after RD 0 0 ns
tRHDZ 2,3 Data float after RD 97 2tCLCL -70 ns
tLLDV 2, 3 ALE low to valid data in 517 8tCLCL-150 ns
tAVDV 2, 3 Address to valid data in 585 9tCLCL-165 ns
tLLWL 2, 3 ALE low to RD or WR low 200 300 3!cLCl. -50 3lel r.1 +50 ns
tAvw 2, 3 Address valid to WR low or RD low 203 4tCLCL-130 ns
tovwx 2, 3 Data valid to WR transition 23 tCLCL-60 ns
tOIlll'lH 2, 3 Data vaid to WR high 433 7tCI CL -150 ns
tWHOX 2, 3 Data hold after WR 33 tCLCL-8 ns
tRLAZ 2,3 RD low to address float 20 20 ns
tWHLH 2, 3 RD or WR high to ALE high 43 123 tCLCL-40 tCLCL+40 ns
External Clock
tCHCX 5 High time 20 20 ns
tCLCX 5 Low time 20 20 ns
tCLCH 5 Rise time 20 20 ns
tCHCL 5 Fall time 20 20 ns
Shift Register
tXLXL 4 Serial port clock cycle time 1.0 12tCLCL ).IS
tOVXH 4 Output data setup to clock rising edge 700 10tCLCL-133 ns
tXHOX 4 Output data hold after clock rising edge 50 2tCLCL-117 ns
tXHDX 4 Input data hold after clock rising edge 0 0 ns
tXHDV 4 Clock rising edge to input data valid 700 10tCLCL-133 ns
NOTES:
1. Parameters are valid over operatingteFfENture
2. Lead capacitance for port 0, ALE, and S
range unless otherwise specified.
- 100pF. load capacitance for all other outputs = 80pF.
EXPLANATION OF THE AC SYMBOLS P- PSEN

Each timing symbol has five characters. The first character is Q - Output data
always 't' (- time). The other characters, depending on their R - RD signal
positions, indicate the name of a signal or the logical status of t - Time
that signal. The designations are: V-Valid
A - Address W - WRsignal
C - Clock X - No longer a valid logic level
D - Input data Z - Float
H - Logic level high Examples: tAVLL = Time for address valid to ALE low.
I - Instruction (program memory contents) tLLPL - Time for ALE low to J5SEN low.
L - Logic level low, or ALE
February 1989 1-119

Single-Chip 8-Bit Microcontroller SCN8031 AH /SCN8051 AH
ALE
PSEiii _ _ _J
PORTO _ _ _J
PORT 2 _ _ _ _J
Figure 1. External Program Memory Read Cycle
ALE
1 0 - - - - - tllDV - - - . - I
--~~---tRlRH-----.-I
PORT 0 AO-A? FROM PCl
~----------tAVDV-----~
--~
PORT 2 P2.0-P2.? OR A8-A15 FROM DPH A8-A15 FROM PCH
February 1989 1-120

ALE
----~-----tWlWHI------~
1o--l---tOVWH-----ooI
1.----.;""'...---.1.
PORT 0 DATA OUT AO-A? FROM PCl
INSTRUCTION o 2 3 4 5 6 7 8
ALE
tOVXH H r- t XHOX
OUTPUT DATA
\\-_---1 '--_--' \-_---1 " - _ - ' \-_---1 '--_--' \-_---1 1...-_-'
T
WRITE TO SBUF
I INPUT DATA I ____________J'. "I' I
f
CLEAR RI t
SET RI
Figure 4. Shift Register Mode Timing
February 1989 1-121

O.45V
t o - - - - - - t cLCL -----of
Figure 5. External Clock Drive
Vcc-O.5
O.45V
=x O.2Vcc+O.9
_,-O;";';;,2V,;.;c;.,;c,;.;-.;;.O;.,;.1_ __
>C Timing
Reference
Points
<
AC inputs during testing are driven at Vcc-0.5
For timing purposes, a port is no longer floating
for a logic "1" and 0.45V for a logic "0".
when a 100mV change from load voltage occurs,
Timing measurements are made at VIH min for
and begins to float when a 100mV change from
a logic "1" and V IL max for a logic "0".
the 10adedVOHIVOL level occurs.IOHIlOL~±20mA.
Figure 6. AC Testing Input/Output

Figure 7. Float Waveform
Vee
. -_ _ _ _....lcC
VCC
!
Vce Vee
PO
RST Ei':
(NC) XTALl
CLOCK XTAL2
SIGNAL Vss
Figure 8. Icc Test Condition, Active Mode

All other pins are disconnected
0.45V
~------tCLCL-----~
Figure 9. Clock Signal Waveform for Icc Tests in Active and Idle Modes
tClCH tCHCL = 5ns =
February 1989 1-122

Signetics SC80C31B/SC80C51B
CMOS Single-Chip 8-Bit
Microcontroller
DESCRIPTION FEATURES PIN CONFIGURATION (Cont)
oo·"tJ
The Signetics SC80C31 B/SC80C51 B is a • SCN8031/SCN80S1/SC80CS1
high-performance microcontroller fabri- compatible INDEX
cated with Signetics high-density CMOS - 4K x 8 ROM
technology. The CMOS SC80C31B/ 7 0 39
- 128 x 8 RAM
SC80C51 B is functionally compatible
with the NMOS SCN8031/SCN8051 mi-
- Two 16-bit counter/timers
Lee
crocontrollers. The Signetics CMOS - Full duplex serial channel
technology combines the high speed and - Boolean processor 17 29
density characteristics of HMOS with • Memory addressing capability
the low power attributes of CMOS. - 64K ROM and 64K RAM 18 28
Signetics' epitaxial substrate minimizes • Power control modes: TOP VIEW
latch-up sensitivity. - Idle mode Pin Function Pin Function
- Power-down mode 1 NC 23 NC
The SC80C31 B/SC80C51 B contains a 2 P1.0 24 P2.0/A8
4K x 8 ROM, a 128 x 8 RAM, 32 I/O • CMOS and TTL compatible 3 P1.1 25 P2.1/A9
lines, two 16-bit counter/timers, a five- • Three speed ranges at Vee = 4 P1.2 26 P2.2/A10
5 P1.3 27 P2.3/A11
source, two priority level nested interrupt SV ±20% 6 P1.4 28 P2.4/A12
structure, a serial I/O port for either - 3.S to 12MHz 7 P1.5 29 P2.5/A13
multi-processor communications, I/O ex- - 3.S to 16MHz 8 P1.6 30 P2.6/A14
pansion or full duplex UART, and on-chip 9 P1.7 31 P2.7/A15
- O.S to 12MHz 10 RST 32 PSrN
oscillator and clock circuits. • Three package styles 11 RxD/P3.0 33 ALE
12 NC 34 NC
In addition, the SC80C31 B/SC80C51 B 13 TxD/P3.1 35 D(
has two software selectable modes of PIN CONFIGURATION 14 1l\JTO/P3.2 36 PO.7/AD7
power reduction - idle mode and power- 15 I1\i'I'i/P3.3 37 PO.6/AD6
16 TO/P3.4 38 PO.5/AD5
down mode. The idle mode freezes the 17 T1/P3.5 39 PO.4/AD4
CPU while allowing the RAM, timers, se- P1.0 :::;: I:ro Vee 18 iNrl/P3.6 40 PO.3/AD3
rial port, and interrupt system to con- P1.1 ~ ~ PO.O/ADO 19
20
lTI)/P3.7
XTAL2
41 PO.2/AD2
tinue functioning. The power-down mode 42 PO.1/AD1
P1.2.l ~ PO.1/AD1 21 XTAL1 PO.O/ADO
43
saves the RAM contents but freezes the
P1.3~ ~ PO.2/AD2 22 Vss 44 Vee
oscillator, causing all other chip func-
P1.4~ ~ PO.3/AD3 6 1 40
'8'"
tions to be inoperative.
P1.514 ~ PO.4/AD4
LOGIC SYMBOL P1.6~ ~ PO.5/AD5

P1.7~ ~ PO.6/AD6
QFP
RST 9 ~ ~7/AD7
~:~;:::~ ~ DIP 31 EA
to ALE 17 0 29
INTO/P3.2 ~ tePSEN 18 28
INT1/P3.3g ~ P2.7/A15 TOP VIEW
TO/P3.4 14
Pin Function Pin Function
~ P2.6/A14
1 NC 23 Vss
..:!2!P3.5 ~ ~ P2.5/A13 2 P1.0 24 P2.0/A8
WR/P3.6 ~ ~ P2.4/A12 3 P1.1 25 P2.1/A9
4 P1.2 26 P2.2/A10
RD/P3.7 ~ ~ P2.3/A11 5 P1.3 27 P2.3/A11
XTAL2 ~ ~ P2.2/A10 6 P1.4 28 P2.4/A12
7 P1.5 29 P2.5/A13
XTAL1 ~ ~ P2.1/A9 P1.6 P2.6/A14
8 30
Vss &Q t£1. P2.01 A8 9 P1.7 31 P2.7/A15
10 RST 32 J5SrFJ
TOP VIEW 11 RxD/P3.0 33 ALE
12 NC 34 NC
13 TxD/P3.1 35 l:A
14 TmQ/P3.2 36 PO.7/AD7
15 iNTi IP3.3 37 PO.6/AD6
16 TO/P3,4 38 PO.5/AD5
17 T1/P3.5 39 PO,4/AD4
18 WR/P3.6 40 PO.3/AD3
19 RD/P3.7 41 PO.2/AD2
22 Vss 44 Vee
February 1989 1-123

CMOS Single-Chip 8-Bit Microcontroller SC80C31 B/SC80C51 B
ORDERING INFORMATION PART NUMBER SELECTION
ROM
ROM~:;;r~BcCCC1C
Temperature and Frequency
less ROM
Package
:uIX: ROM Pattern No. 8C80C31 BCCN40 8C80C51 BCCN40 3.5 to 12MHz
o to +70°C plastic DIP
3 - ROMless Applies to masked ROM versions
5 _ ROM only. Number will be assigned by 8C80C31 BCGN40 8C80C51 BCGN40 o to +70°C plastic DIP 3.5 to 16MHz
Signetics. Contact Signetics sales 8C80C31 BCBN40 8C80C51 BCBN40 0.5 to 12MHz
o to + 70°C plastic DIP
office for ROM pattern submission
requirements. 8C80C31 BCCA44 8C80C51 BCCA44 o to + 70°C plastic LCC 3.5 to 12MHz
Pins 8C80C31 BCGA44 8C80C51 BCGA44 o to + 70°C plastic Lee 3.5 to 16MHz
40 - 40-pin
44 - 44-pin 8C80C31 BCBA44 8C80C51 BCBA44 o to +70 0 C plastic LCC 0.5 to 12MHz
Package 8C80C31 BACN40 8C80C51 BACN40 -40 to +85°C plastic DIP 3.5 to 12MHz
A - Plastic LCC
N - Plastic DIP 8C80C31 BAGN40 8C80C51 BAGN40 -40 to +85 0 C plastic DIP 3.5 to 16MHz
B - Plastic OFP
8C80C31 BACA44 8C80C51 BACA44 -40 to +85°C plastic LCC 3.5 to 12MHz
Speed
B - 0.5 to 12MHz 8C80C31 BAGA44 8C80C51 BAGA44 -40 to +85°C plastic LCC 3.5 to 16MHz
C - 3.5 to 12MHz 8C80C31 BCCB44 8C80C51 BCCB44 o to +70°C plastic OFP 3.5 to 12MHz
G - 3.5 to 16MHz
Operating Temperature Range 8C80C31 BCGB44 8C80C51 BCGB44 o to + 70°C plastic OFP 3.5 to 16MHz
A - -40°C to +85°C
C - OOC to +70 0 C
BLOCK DIAGRAM
PO.D-PIl.7 P2.O-P2.7
- - - - - - - - - - P--!~"" --------l
PCON SOON TMOD TooN

THO no THI
SBUF IE IP
PSDi ~_.r--_r_::1
ALE
EA
RST
PJ.o-PJ.7
February 1989 1-124

PIN DESCRIPTION
PIN NO.
MNEMONIC LCC! TYPE NAME AND FUNCTION
DIP
QFP
23 I Ground: OV reference. (QFP only)
Vee 40 44 I Power Supply: This is the power supply voltage for normal, idle, and power-down op-
eration.
PO.O-PO.? 39-32 43-36 I/O Port 0: Port 0 is an open-drain, bidirectional I/O port. Port 0 pins that have 1s written
ory. In this application, it uses strong internal pullups when emitting 1s. Port 0 also
outputs the code bytes during program verification in the SC80C31 B/SC80C51 B. Ex-
ternal pull-ups are required during program verification.
P1.0-P1.7 1-8 2-9 I/O Port 1: Port 1 is an 8-bit bidirectional I/O port with internal pullups. Port 1 pins that
of the internal pullups. (See DC Electrical Characteristics: IILl. Port 1 also receives the
low-order address byte during program memory verification.
P2.0-P2.7 21-28 24-31 I/O Port 2: Port 2 is an 8-bit bidirectional I/O port with internal pullups. Port 2 pins that
because of the internal pullups. (See DC Electrical Characteristics: IILl. Port 2 emits the
application, it uses strong internal pullups when emitting 1s. During accesses to exter-
nal data memory that use 8-bit addresses (MOVX @Ri), port 2 emits the contents of the
P2 special function register.
P3.0-P3.7 10-17 11, I/O Port 3: Port 3 is an 8-bit bidirectional I/O port with internal pullups. Port 3 pins that
because of the pUll-Ups. (See DC Electrical Characteristics: IILl. Port 3 also serves the
special features of the SC80C51 family, as listed below:
11 13 0 TxD (P3.1): Serial output port
13 15 I INn (P3.3): External interrupt
15 17 I I1JP3.5): Timer 1 external input
16 18 0 WR (P3.5): External data memory write strobe
17 19 0 RD (P3.7): External data memory read strobe
ALE 30 33 I/O Address Latch Enable: Output pulse for latching the low byte of the address during an
one ALE pulse is skipped during each access to external data memory.
- -
PSEN 29 32 0 Program Store Enable: The read strobe to external program memory. When the SC80-
C31 B/SC80C51 B is executing code from external program memory, PSEN is activated
twice each machine cycle, except that two PSEN activations are skipped during each
access to external data memory. PSEN is not activated during fetches from internal
program memory.
EA 31 35 I External Access Enable: EA must be externally held low to enable.!b..e device to fetch
code from external program memory locations OOOOH and OFFFH. If EA is held high, the
address greater than OFFFH.
XTAL1 19 21 I Crystal 1: Input to the inverting oscillator amplifier and input to the internal clock gen-
erator circuits.
XTAL2 18 20 0 Crystal 2: Output from the inverting oscillator amplifier.
February 1989 1-125

OSCILLATOR CHARACTERISTICS RESET idle mode is activated. The CPU con-

XTAL1 and XTAL2 are the input and out- A reset is accomplished by holding the tents, the on-chip RAM, and all of the
put, respectively, of an inverting ampli- RST pin high for at least two machine special function registers remain intact
fier. The pins can be configured for use cycles (24 oscillator periods), while the during this mode. The idle mode can be
as an on-chip oscillator, as shown in the oscillator is running. To insure a good terminated either by any enabled inter-
logic symbol, page 1. power-on reset, the RST pin must be rupt (at which time the process is picked
high long enough to allow the oscillator up at the interrupt service routine and
To drive the device from an external time to start up (normally a few milli- continued), or by a hardware reset
clock source, XTAL1 should be driven seconds) plus two machine cycles. At which starts the processor in the same
while XTAL2 is left unconnected. There power-on, the voltage on Vee and RST manner as a power-on reset.
are no requirements on the duty cycle of must come up at the same time for a
the external clock signal, because the proper start-up. POWER-DOWN MODE
input to the internal clock circuitry is In the power-<!own mode, the oscillator
through a divide-by-two flip-flop. How- IDLE MODE is stopped and the instruction to invoke
ever, minimum and maximum high and In the idle mode, the CPU puts itself to power-<!own is the last instruction exe-
low times specified in the data sheet sleep while all of the on-chip peripherals cuted. Only the contents of the on-chip
must be observed. stay active. The instruction to invoke the RAM are preserved. A hardware reset is
idle mode is the last instruction executed the only way to terminate the power-
in the normal operating mode before the down mode. The control bits for the re-
duced power modes are in the special
function register PCON.
Table 1 shows the state of I/O ports

during low current operating modes.
Table 1. External Pin Status During Idle and Power-Down Modes
Mode Program Memory ALE PSEN Port 0 Port 1 Port 2 Port 3

Idle Internal 1 1 Data Data Data Data
Idle External 1 1 Float Data Address Data
Power-down Internal 0 0 Data Data Data Data
Power-down External 0 0 Float Data Data Data
February 1989 1-126

ABSOLUTE MAXIMUM RATlNGS1. 2. 3

Storage temperature range 65 to +150 °C
Voltage on any other pin to VSS -0.5 to + 6.5 V
Power dissipation (based on package heat transfer
1.5 W
limitations, not device power consumption)
NOTES:
fUnctional operation of the device at these or any conditions other than those described in the AC and DC Electrical Characteristics sec-
2. This product includes circuitry specifically desig ned for the protection of its internal devices from the damag ing effects of excessive static
charge. Nonetheless, it is suggested that conventional precautions be taken to avoid applying voltages greater than the rated maxima.
3. Parameters are valid over operating temperature range unless otherwise specified. All voltages are with respect to Vss unless otherwise
noted.
DC ELECTRICAL CHARACTERISTICS TA - O°C to +70°C or TA - -40°C to +B5°C, Vcc - 5V ±20%, VSS - OV

Limits
Min Typical1 Max
VIL Input low voltage, except EA -0.5 0. 2Vcc-0.1 V
VIL1 Input low voltage to EA 0 0. 2Vcc-0.3 V

VIH Input high voltage, except XTAL1, RST 0. 2Vcc+· 9 Vcc+0.5 V
VIH1 Input high voltage, XTAL 1, RST 0. 7Vcc Vcc+0.5 V
VOL Output low voltage, ports 1, 2, 3 IOL - 1.6mA2 0.45 V
VOL1 Output low voltage, port 0, ALE, PSEN IOL - 3.2mA2 0.45 V
VOH Output high voltage, ports 1, 2, 3 Vcc - 5V±10%,

IOH - - 6O IlA 2.4 V
IOH - - 251lA 0. 75Vcc V
IOH - -1 01lA 0. 9Vcc V

VOH1 Output high voltage (port 0 in external bus Vcc - 5V±10%,
mode, ALE, PSEN)3 IOH - -BOO IlA 2.4 V
IOH - - 3OOIlA 0. 75Vcc V
IOH - -BOllA 0. 9Vcc V

IlL Logical 0 input current, ports 1, 2, 3 VIN - 0.45V -50 IlA
ITL Logical 1-to-0 transition current, ports 1, 2, 3 See note 4 -650 IlA
III Input leakage current, port 0 VIN - VIL or VIH ±10 IlA
Icc Power supply current: See note 6
Active mode @ 12MHz5 11.5 25 mA
Idle mode @ 12MHz5 1.3 4 mA
Power down mode 3 50 IlA
RRST Internal reset pulidown resistor 50 300 kQ
NOTES.
1. Typical ratings are based on a limited number of samples taken from early manufacturing lots and are not guaranteed. The values listed are
at room temperature, 5V.
2. Capacitive loading on ports 0 and 2 may cause spurious noise to be superimposed on the VOLs of ALE and ports 1 and 3. The noise is due
to external bus capacitance discharging into the port 0 and port 2 pins when these pins make 1-to-0 transitions during bus operations.
In the worst cases (capacitive loading> 100pF), the noise pulse on the ALE pin may exceed O.BV. In such cases, it may be desirable to
qualify ALE with a Schmitt Trigger. or use an address latch with a Schmitt Trigger STROBE input.
3. Capacitive loading on ports 0 and 2 may cause the VOH on ALE and PSEN to momentarily fall below the 0.9VCC specification when the
address bits are stabilizing.
4. Pins of ports 1, 2, and 3 source a transition current when they are being externally driven from 1 to O. The transition current reaches its
maximum value when VIN is approximately 2V.
5. ICC MAX at other frequencies is given by:
Active mode: ICCMAX - 0.94 X FREO + 13.71
Idle mode: ICCMAX - 0.14 X FREO + 2.31
where FREQ is the external oscillator frequency in MHz. ICCMAX is given in mA. See Figure B.
6. See Figures 9 through 12 for ICC test conditions.
February 1989 1-127

AC ELECTRICAL CHARACTERISTICS TA - O°C to +70°C or TA - -40°C to +B5°C, VCC - 5V ±20%, VSS - OV1, 2
SYMBOL FIGURE PARAMETER UNIT
Min Max Min Max
Program Memory
l/tClCl 1 Oscillator frequency: Speed Versions
SCBOC31B/SCBOC51B B 0.5 12 MHz
SCBOC31B/SCBOC51B C 3.5 12 MHz
SCBOC31B/SCBOC51B G 3.5 16 MHz
tlHll 1 ALE pulse width 127 2tClCl -40 ns
tAVlL 1 Address valid to ALE low 2B t0101-55 ns
tllAX 1 Address hold after ALE low 4B tClCl -35 ns
tlLIV 1 ALE low to valid instruction in 234 4tClCL -100 ns
tllPl 1 ALE low to PSEN low 43 tClCl -40 ns
tp PH 1 PSEN pulse width 205 3tClCl -45 ns
tpLiV 1 PSEN low to valid instruction in 145 3tclCl -105 ns
tpXIZ 1 Input instruction float after PSEN 59 tClCl -25 ns
tAVIV 1 Address to valid instruction in 312 5tClCl -105 ns
tplAZ 1 PSEN low to address float 10 10 ns
Data Memory
tRlRH 2, 3 RD pulse width 400 6tClCl -100 ns
tWlWH 2, 3 WR pulse width 400 6tClCl -100 ns
tRIDV 2, 3 RD low to valid data in 252 5tcLCL -165 ns
tRHDZ 2, 3 Data float after RD 97 2tClCL -70 ns
tllDV 2, 3 ALE low to valid data in 517 BtClCl -150 ns
tAVDV 2, 3 Address to valid data in 5B5 9tCLCl -165 ns
tllWl 2,3 ALE low to RD or WR low 200 300 3tClCl -50 3tClCl +50 ns
tAVWL 2, 3 Address valid to WR low or RD low 203 4tOLCI -130 ns
tQVWX 2, 3 Data valid to WR transition 23 tCLCl-60 ns
IRlAZ 2,3 RD low 10 address float 0 0 ns
tWHlH 2, 3 RD or WR high to ALE high 43 123 tClCL -40 tClCl+40 ns
External Clock
tClCX 5 Low time 20 20 ns
tClCH 5 Rise time 20 20 ns
tCHCl 5 Fall time 20 20 ns
Shift Re ister
IXlXl 4 Serial port clock cycle time 1.0 12tClCl f1S
tOVXH 4 Output data setup to clock rising edge 700 10tClCl-133 ns
tXHOX 4 Output data hold after clock rising edge 50 2tClCl -117 ns
tXHDV 4 Clock rising edge to input data valid 700 1OtClCl -133 ns
NOTES:
2. Load capacitance for port O. ALE, and PSEN ~ 100pF. load capacitance for all other outputs ~ 80pF.

Each timing symbol has five characters. The first character is Q - OUIPuI dala
always 'I' (- time). The other characters, depending on their R - RD signal
positions, indicate the name of a signal or the logical stalus of t - Time
that Signal. The designations are: V - Valid
A - Address W - WR signal
D - I nput data Z - Float
H - Logic level high Examples: tAVll - Time for address valid to ALE low.
I - I nstruction (program memory contents) IllPl - Time for ALE low to PSEN low.
February 1989 1-128

ALE
PSEN _ _ _J
PORTO _ _ _J
1o-----tAVIV----oI
PORT 2 AB-A15 A8-A15
ALE
10------- tllDV - - - - o j
--..----I RlRH ----.I
PORTO AO-A7 FROM PCl
PORT 2 --- ~-----IAVDV--------~
P2.0-P2.7 OR A8-A15 FROM DPH A8-A15 FROM PCH
February 1989 1-129

ALE
- - - - - - - WlWHI-----I
PORTO DATA OUT AO-A? FROM PCl
ALE
tOVXH HI t XHOX
OUTPUT DATA
\,-_~ , " - _ - J ' - _ - - ' ' - - _....... ' - _ - - ' ' - - _ - J ' - _ - - ' '--_..J
f
WRITE TO SBUF
I INPUT DATAl _ _ _ _ _--'
f
CLEAR RI t
SET RI
February 1989 1-130

O.45V
t CHCL
~---------tCLCL--------~
Vcc-O.5
0.45V
=x O.2Vcc+O.9
_:..;O::;.;;.2V;,;c;;;;c;,..-.;:.O.;.:.1_ __
>C Timing
Reference
Points
<
AC inputs during testing are driven at Vcc-O.S
for a logic "1" and O.4SV for a logic "0".
the loaded VOHIVOL level occurs.IOH/1oL ~± 20mA.

30
MAX
ACTIVE MODE
25
20
«
f
E 15
0
~
10
5 ~---+~~+----4----4MAX
IDLE MODE
TVP(1)
~~:±====:t::==1:==~IDLEMODE
4MHz BMHz 12MHz 16MHz
FREQ AT XTAL1
Figure 8. Icc vs. FREQ

Valid only within frequency specifications of the device under test
February 1989 1-131

Vee Vee
. -_ _ _ _-il,ee
Vee
l
Vee
Vee
RST
RST
(NC) XTAL2 XTAL2

CLOCK CLOCK (NC) XTAL1
XTAL1
SIGNAL Vss SIGNAL Vss
Figure 10. Icc Test Condition, Idle Mode

0.45V
1-----tcLcL------.I
tCLCH =
tCHCL =
5ns
Vee
,-____-ilee
Vee
l
Vee
RST
(NC) XTAL2
XTAL1
Vss
Figure 12. Icc Test Conditions, Power Down Mode

All other pins are disconnected. VCC = 2V to 5.5V
February 1989 1-132

Signefics SC87C51
CMOS Single-Chip 8-Bit EPROM
Microcontroller

The Signetics SC8lCSl is a high-per- • SCN8031/SCN8051/SC80C51
forma nee microcontroller fabricated with compatible
Signetics high-<Jensity CM OS technol- - 4K x 8 EPROM P1.0~
r-:"
'40 Vee
ogy. The CMOS SC8lCSl is functionally
compatible with the NMOS SCN8031/
- 128 x 8 RAM P1.1 2 ~ PO.O/ADO
SCN80S1 and SC80CSI microcontrollers.

- Two 16-bit counter/timers P1.2 ~ ~ PO.1/AD1
The Signetics CMOS technology com- - Full duplex serial channel P1.3 ~ ~ PO.2/AD2
bines the high speed and density charac- - Boolean processor P1.4 ~ ~ PO.3/AD3
teristics of HMOS with the low power at- • Memory addressing capability P1.5 ~ ~ PO.4/AD4
tributes of CMOS. Signetics' epitaxial - 64K ROM and 64K RAM P1.6 ~ ~ PO.5/AD5
substrate minimizes latch-up sensitivity. • Power control modes: P1.7 8 § PO.6/AD6
- Idle mode
The SC8lCSl contains a 4K x 8 RST ~ ~ ~.7/AD7
- Power-down mode
EPROM, a 128 x 8 RAM, 32 I/O lines, RxD/P3.0 ,lg DIP 31 EA/vpp
two 16-bit counter/timers, a five-source, • CMOS and TTL compatible
• Three speed ranges at Vcc =
TxD/P3.1 11 ~ ALE/PROG
two priority level nested interrupt struc- INTO/P3.2 12 29 PSEN
ture, a serial I/O port for either multi-
processor communications, I/O expan-
5V ±10%
- 3.5 to 12MHz ii\ii'1/P3.3 ~ ~ P2.7/A15
TO/P3.4 ~ ~ P2.6/A14
sion or full duplex UART, and on-chip - 3.5 to 16MHz
oscillator and clock circuits. 2:1.!P3.5 ~5 ~ P2.5/A13
- 0.5 to 12MHz
WR/P3.6 16 ~ P2.4/A12
• Four package styles
In addition, the SC8lCSl has two soft-
• Extended temperature ranges RD/P3.7 p)l E; P2.3/A11
ware selectable modes of power reduc-
• OTP package available XTAL2 18 I¥ P2.2/A10
tion - idle mode and power-<Jown mode.
The idle mode freezes the CPU while al- XTAL1 ~ I¥. P2.1/A9
lowing the RAM, timers, serial port, and Vss ~ 21 P2.0/A8
interrupt system to continue functioning. TOP VIEW
The power-<Jown mode saves the RAM INDEX
contents but freezes the oscillator, caus- LOGIC SYMBOL CORNER 6 1 40
EJ
ing all other chip functions to be inop-
erative.
LCC
17 29
18 28
TOP VIEW
1 NC 23 NC
2 P1.0 24 P2.0/A8
3 P1.1 25 P2.1/A9
4 P1.2 26 P2.2/A10
5 P1.3 27 P2.3/A11
6 P1.4 28 P2.4/A12
7 P1.5 29 P2.5/A13
8 P1.6 30 P2.6/A14
9 P1.7 31 P2.7/A15
10 RST 32 PSE"N
11 RxD/P3.0 33 ALE/PROG
12 NC 34 NC
13 TxD/P3.1 35 bli/Vpp
14 1N'f5/P3.2 36 PO.7/AD7
15 j'lfi"1'/P3.3 37 PO.6/AD6
16 TO/P3.4 38 PO.S/ADS
17 T1/P3.S 39 PO.4/AD4
18 Wli/P3.6 40 PO.3/AD3
19 Fill/P3.7 41 PO.2/AD2
C1, C2 ~ JOpF ±1OpF for cryaI:a. 20 XTAL2 42 PO.1/AD1
C1, C2 = 40pF ±1OpF for ceramic 21 XTAL1 43 PO.O/ADO
I'lIIIOnatorw 22 Vss 44 Vee
February 1989
1-133
CMOS Single-Chip 8-Bit EPROM Microcontroller SC87C51

Part Number Speed Temperature and Package
SC87C51 c ecce SC87C51CCF40 3.5 to 12MHz o to +70 0 C, ceramic DIP
SC87C51 CGF40 3.5 to 16MHz o to +70 0 C. ceramic oJP
SC87C51 CBF40 0.5 to 12MHz o to +70°C, ceramic DIP'"
SC87C51 CCL44 3.5 to 12MHz o to +70 0 C, ceramic Lee
SC87C51 CGL44 3.5 to 16MHz a to +70 0 e, ceramic Lee
SC87C51 CBL44 0.5 to 12MHz o to +70 0 C, ceramic LeC'"
SC87C51 CCN40 3.5 to 12MHz o to + 70°C, plastic DIP
SC87C51 CGN40 3.5 to 16MHz o to +70°C, plastic DIP
OPERATING SC87C51 CBN40 0.5 to 12MHz o to +70 oC, plastic DIP'
TEMPERATURE RANGE o to +70 oC, plastic LCC
A - -40 °c
to +85 °c 40 = 40 pin DIP SC87C51 CCA44 3.5 to 12MHz
44 = 44 pin LCC SC87C51CGA44 3.5 to 16MHz o to +70 oC, plastic LCC
C- a °c
to +70 °c SC87C51 CBA44 0.5 to 12MHz o to +70 oC, plastic LCC'
SPEED PACKAGE SC87C51 ACN40 3.5 to 12MHz -40 to +85°C, plastic DIP
B - 0.5 to 12MHz A - Plastic LCC SC87C51 AGN40 3.5 to 16MHz -40 to +85°C, plastic DIP
C - 3.5 to 12MHz F - Ceramic DIP SC87C51 ACA44 3.5 to 12MHz -40 to +85°C, plastic LCC
G - 3.5 to 16MHz L - Ceramic LCC SC87C51 AGA44 3.5 to 16MHz -40 to +85 0 C, plastic LCC
N - Plastic DIP SC87C51 ABN40 0.5 to 12MHz -40 to +85°C, plastic DIP'
SC87C51 ABA44 0.5 to 12MHz -40 to +85°C, plastic LCC'
SC87C51 ACF40 3.5 to 12MHz -40 to +85°C, ceramic DIP
SC87C51 ACL44 3.5 to 12MHz -40 to +85°C, ceramic Lee
SC87C51ABL44 0.5 to 12MHz -40 to +85°C, ceramic LeC"
SC87C51AGL44 3.5 to 16MHz -40 to +85°C, ceramic Lee
SC87C51 AGF40 3.5 to 16MHz -40 to +85 0 C, ceramic DIP
SC87C51ABF40 0.5 to 12MHz
.
-40 to +85°C, ceramic DIP'"
Contact Factory
BLOCK DIAGRAM
PO.o-PO,7
-------l
PCON SOON TIIO TCON

THO TLO THI
TLI
SBUF IE IP
Pl.cH'I.7
February 1989 1-134

PIN DESCRIPTION
PIN NO.
MNEMONIC 1----.---1 TYPE NAME AND FUNCTION
DIP LCC
Vee 40 44 I Power Supply: This is the power supply voltage for normal, idle, and power-down op-
eration.
PO.0-PO.7 39-32 43-36 1/0 Port 0: Port 0 is an open-drain, bidirectional 1/0 port. Port 0 pins that have ls written
ory. In this application, it uses strong internal pullups when emitting ls. Port 0 also
outputs the code bytes during program verification in the SC87C51. External pull-ups
are required during program verification.
Pl.0-Pl.7 1-8 2-9 1/0 Port 1: Port 1 is an 8-bit bidirectional 1/0 port with internal pUll-ups. Port 1 pins that
of the internal pull-ups. (See DC Electrical Characteristics: IILl. Port 1 also receives the
low-order address byte during program memory verification.
P2.0-P2.7 21-28 24-31 110 Port 2: Port 2 is an 8-bit bidirectional 110 port with internal pUll-ups. Port 2 pins that
because of the internal pullups. (See DC Electrical Characteristics: IILl. Port 2 emits the
application, it uses strong internal pull-ups when emitting ls. During accesses to
external data memory that use 8-bit addresses (MOVX @Ri), port 2 emits the contents
of the P2 special function register.
P3.0-P3.7 10-17 11, 110 Port 3: Port 3 is an 8-bit bidirectional 110 port with internal pullups. Port 3 pins that
because of the pUll-ups. (See DC Electrical Characteristics: IILl. Port 3 also serves the
special features of the SC80C51 family, as listed below:
15 17 I !!JP3.5): Timer 1 external input
16 18 o WR (P3.B): External data memory write strobe
17 19 o RD (P3.7): External data memory read strobe
ALE/PROG 30 33 110 Address Latch Enable/Program Pulse: Output pulse for latching the low byte of the
address during an access to external memory. In normal operation, ALE is emitted at a
constant rate of 1/6 the oscillator frequency, and can be used for external timing or
clocking. Note that one ALE pulse is skipped during each access to external data
memory. This pin is also the progam pulse input (PROG) during EPROM programming.
PSEN 29 32 o Program Store Enable: The read strobe to external progU!!!!..J!1emory. When the
SC87C51 is executing code from external program memory, PSEN is activated twice
each machine cycle, exceRt that two PSEN activations are skipped during each access
to external data memory. PSEN is not activated during fetches from internal program
memory.
EAlVpp 31 35 I External Access Enable/Programming Supply Voltage: EA must be externally held low
to enable the device to fetch code from external program memory locations OOOOH
through OFFFH. If EA is held high, the device executes from internal program memory
unless the program counter contains an address greater than OFFFH. This pin also
receives the 12.75V programming supply voltage (Vpp) during EPROM programming.
XTAL1 19 21 I Crystal 1: Input to the inverting oscillator amplifier and input to the internal clock gen-
erator circuits.
XTAL2 18 20 o Crystal 2: Output from the inverting oscillator amplifier.
February 1989 1-135

CMOS Single-Chip 8-Sit EPROM Microcontroller SC87C51
OSCILLATOR CHARACTERISTICS in the normal operating mode before the DESIGN CONSIDERATIONS
XTAL1 and XTAL2 are the input and out- idle mode is activated. The CPU con- At power-on, the voltage on Vee and
put, respectively, of an inverting ampli- tents, the on-chip RAM, and all of the RST must come up at the same time for
fier. The pins can be configured for use special function registers remain intact a proper start-up.
as an on-chip oscillator, as shown in the during this mode. The idle mode can be
logic symbol, page 1. terminated either by any enabled inter- When the idle mode is terminated by a
rupt (at which time the process is picked hardware reset, the device normally
To drive the device from an external up at the interrupt service routine and resumes program execution, from where
clock source, XTAL1 should be driven continued), or by a hardware reset it left off, up to two machine cycles be-
while XTAL2 is left unconnected. There which starts the processor in the same fore the internal reset algorithm takes
are no requirements on the duty cycle of manner as a power-on reset. control. On-chip hardware inhibits ac-
the external clock signal, because the cess to internal RAM in this event, but
input to the internal clock circuitry is POWER-DOWN MODE access to the port pins is not inhibited.
through a divide-by-two flip-flop. How- In the power.<Jown mode, the oscillator To eliminate the possibility of an un-
ever, minimum and maximum high and is stopped and the instruction to invoke expected write when idle is terminated
low times specified in the data sheet power.<Jown is the last instruction exe- by reset, the instruction following the
must be observed. cuted. Only the contents of the on-chip one that invokes idle should not be one
RAM are preserved. A hardware reset is that writes to a port pin or to external
IDLE MODE the only way to terminate the power- memory.
In the idle mode, the CPU puts itself to down mode. The control bits for the re-
sleep while all of the on-chip peripherals duced power modes are in the special Table 1 shows the state of liD ports
stay active. The instruction to invoke the function register PCON. during low current operating modes.
idle mode is the last instruction executed

Electric~1 Deviations from Commercial Specifications

for Extended Temperature Range
D.C. and A.C. parameters not included here are the same as in
the commercial temperature range table.
DC ELECTRICAL CHARACTERISTICS TA - -40°C to +85°C, Vee - 5V ±100/0, Vss - OV

Limits
Min Max
VIL Input low volatage (except EA) -0.5 O.2Vee-0.15 V
VIL1 EA 0 0.2Vee-0.35 V
VIH Input high voltage (except XTAL1, RST) 0. 2Vee+ 1 Vee+0.5 V
VIH1 Input high voltage to XTAL1, RST 0.7Vee+0.1 Vee+0.5 V
IlL Logical 0 input current (port 1, 2, 3) VIN - 0.45V -75 ).lA
ITL Logical 1 to 0 transition current (ports 1, 2, 3) VIN - 2.0V -750 ).lA
Icc Power supply current Vee - 4.5-5.5V,
Active mode Frequency range - 35 mA
Idle mode 3.5 to 12MHz 6 rnA
Power down mode 50 ).lA
February 1989 1-136


Oto+700r
Operating temperature under bias °C
-40 to +85
Voltage on EA/vpp pin to Vss o to +13,0 V
Voltage on any other pin to Vss -0,5 to + 6,5 V
1.5 W
NOTES:
noted.
DC ELECTRICAL CHARACTERISTICS TA ~ O°C to +70°C or -40°C to +85°C, Vcc ~ 5V ±10%, Vss ~ OV

Limits
Min Typical Max
VIL Input low voltage, except EA7 -0.5 0. 2Vcc-0 .1 V
VIL1 Input low voltage to EA7 0 0. 2Vcc-O.3 V
VIH Input high voltage, except XTAL 1, RST7 0. 2Vcc+· 9 Vcc+0 .5 V
VIH1 Input high voltage, XTAL 1, RST7 0. 7Vcc Vcc+0 .5 V
VOl1 Output low voltage, port 0, ALE, PSEN IOL - 3.2mA2 0.45 V
VOH Output high voltage, ports 1, 2, 3, ALE, PSEN3 IOH ~ -60j.lA 2.4 V
IOH - -25j.lA 0. 75Vcc V
IOH - -10j.lA 0. 9Vcc V
VOH1 Output high voltage (port 0 in external bus IOH - -800j.lA 2.4 V
mode) IOH - -300 j.lA 0.75Vcc V
IOH - -80j.lA O. 9Vcc V
IlL Logical 0 input current, ports 1, 2, 3 7 VIN ~ 0.45V -50 j.lA

ITL Logical 1-to-0 transition current, ports 1, 2, 3 7 See note 4 -650 j.lA
III Input leakage current, port 0 VIN ~ V IL or VIH ±10 j.lA
Icc Power supply current:? See note 6
Active mode @ 12MHz5 11.5 25 mA
1.3 4 mA
Idle mode @ 12MHz5
3 50 j.lA
Power down mode
RRST Internal reset pulldown resistor 50 300 kg
NOTES:
1. Typical ratings are not guaranteed. The values listed are at room temperature, 5V.
to external bus capacitance discharging into the port 0 and port 2 pins when these pins make 1-to-O transitions during bus operations.
In the worst cases (capacitive loading> 100pF), the noise pulse on the ALE pin may exceed O.SV. In such cases, it may be desirable to
qualify ALE with a Schmitt Trigger, or use an address latch with a Schmitt Trigger STROBE input.
3, Capacitive loading on ports
° and 2 may cause the VOH on ALE and PSEN to momentarily fall below the 0,9VCC specification when the
4. Pins of ports 1, 2, and 3 source a transition current when they are being externally driven from 1 to 0.. The transition current reaches its
5. ICCMAX at other frequencies is given by:
Active mode: ICCMAX - 0,94 X FREO + 13.71
Idle mode: ICC MAX - 0,14 X FREQ + 2,31
where FREQ is the external oscillator frequency in MHz. ICCMAX is given in mA. See Figure 8.
7. These values apply only to TA -= OOC to +70 o C. For TA ""' -40°C to +85°C, see table on page 4.
February 1989 1-137

Min Max Min Max
Program Memory
1/tClCl 1 Oscillator frequency: Speed Versions
SC87C51 B 0,5 12 MHz
SC87C51 C 3,5 12 MHz
SC87C51 G 3,5 16 MHz
tlHll 1 ALE pulse width 127 2tClCl -40 ns
tAVL 1 Address valid to ALE low 28 tClCl-55 ns
tllAX 1 Address hold after ALE low 48 tClCl-35 ns
tLLJV 1 ALE low to valid instruction in 234 4tclcl -100 ns
tllPl 1 ALE low to PSEN low 43 tClCl -40 ns
tpLPH 1 PSEN pulse width 205 3tClCl -45 ns
tpLiV 1 PSEN low to valid instruction in 145 3tClCl-105 ns
tPXIX 1 Input instruction hold after PSEN 0 0 ns
tpXIZ 1 Input instruction float after PSEN 59 tClCl-25 ns
tAYIV 1 Address to valid instruction in 312 5tClCL -105 ns
tplAZ 1 PSEN low to address float 10 10 ns
Data Memory_
tRlRH 2, 3 RD pulse width 400 6tCccL -100 ns
tWlWH 2, 3 WR pulse width 400 6tClCl-100 ns
tRlDV 2, 3 RD low to valid data in 252 5tco[-165 ns
tRH[)7 2, 3 Data float after RD 97 2tClCl -70 ns
'llDV 2, 3 ALE low to valid data in 517 8tClCl -150 ns
tAVD\i 2, 3 Address to valid data in 585 9tcLCL -165 ns
tllWl 2, 3 ALE low to RD or WR low 200 300 3tClCl-50 3tClCl+50 ns
tAVWL 2, 3 Address valid to WR low or RD low 203 4tol 01 -130 ns
tOVWX 2, 3 Data valid to WR transition 23 tClCl -60 ns
tWHOX 2, 3 Data hold after WR 33 t0101-50 ns
tRlAZ 2, 3 RD low to address float 0 0 ns
External Clock
tClCX 5 Low time 20 20 ns
tClCH 5 Rise time 20 20 ns
tCHCl 5 Fall time 20 20 ns
Shift Re ister
tXlXl 4 Serial port clock cycle time 1.0 12tClCl J.lS
tOVXH 4 Output data setup to clock rising edge 700 1OtClCl -133 ns
tXHOX 4 Output data hold after clock rising edge 50 2tClCl -117 ns
tXHDV 4 Clock rising edge to input data valid 700 1OtClCl -133 ns
NOTES:
2. Load capacitance for port 0, ALE, and PSEN - 100pF, load capacitance for all other outputs - 80pF.

always 't' (- time). The other characters, depending on their R - RD signal
that signal. The designations are: V - Valid
A - Address W - WR signal
H - Logic level high Examples: tAVll - Time for address valid to ALE low.
I - Instruction (program memory contents) tllPl - Time for ALE low to PSEN low.
February 1989 1-138

ALE
PORTO
----'
PORT 2
-----'
ALE
Je----- tLLDV - - - - I
t LLWL --1---- tRLRH ------I
tRLDV
tRHDX
PORTO
PORT 2 P2.0-P2.7 OR A8-A15 FROM DPH A8-A15 FROM PCH
February 1989 1-139

ALE "- /
"
I-- tWHLH
I-- t LLWL t WLWH
r-. /
t AVLL I-----<
i-tLLAX-o I- tOVWX
...... t WHOX
PORT 0
~ • Hl()MAg;~~
t
np, ~ DATA OUT K AO-A? FROM PCL INSTR IN
AVWL
PORT 2 )c P2.0-P2.? OR A8-A15 FROM DPH A8-A15 FROM PCH
ALE
tOVXH HI t XHOX
OUTPUT DATA
' ' -_ _-' '-_ _-' '-_ _-' '-_ _-' '-_ _-' '-_ _oJ '-_ _oJ 1..._--'
T
WRITE TO SBUF
,'NPUT DATA, _ _ _ _ _....1
f
CLEAR RI
SET RI
February 1989 1-140

0.45V
~----------tCLCL--------~
VCC-O.5=>C O.2Vcc+O.9
0.45V _-.::;O.;,:;2..:.V,:;.cc:;.-..,;O:,;..;.1_ __
C Timing
Reference
Points
<
a logic" 1" and V IL max for a logic "0".
the loaded VOHIVOL level occurs.IOH /1 0L2± 20mA.

EPROM CHARACTERISTICS applied to port O. RST, PSEN and pins shown in Figure 15. The other pins are
The SC87C51 is programmed by using a of ports 2 and 3 specified in Table 2 are held at the "Verify Code Data" levels in-
modified Quick-Pulse Programming" al- held at the "Program Code Data" levels dicated in Table 2. The contents of the
gorithm. It differs from older methods in indicated in Table 2. The ALE/PROG is address location will be emitted on port
the value used for Vpp (programming pulsed low 25 times as shown in Figure O. External pull-ups are required on port
supply voltage) and in the width and 14. a for this operation.
number of the ALE/PROG pulses.
To program the encryption table, repeat If the encryption table has been pro-
The SC87C51 contains two signature the 25 pulse programming sequence for grammed, the data presented at port a
bytes that can be read and used by an addresses a through 1 FH, using the will be the exclusive NOR of the gram
EPROM programming system to identify "Pgm Encryption Table" levels. Do not byte with one of the encryption bytes.
the device. The signature bytes identify forget that after the encryption table is The user will have to know the encryp-
the device as an SC87C51 manufactured programmed, verification cycles will pro- tion table contents in order to correctly
by Signetics Corporation. duce only encrypted data. decode the verification data. The en-
cryption table itself cannot be read out.
Table 2 shows the logic levels for To program the lock bits, repeat the 25
reading the signature byte, and for pro- pulse programming sequence using the Reading the Signature Bytes
gramming the program memory, the en- "Pgm Lock Bit" levels. After one lock bit The signature bytes are read by the
cryption table, and the lock bits. The is programmed, further programming of same procedure as a normal verification
circuit configuration and waveforms for the code memory and encryption table is of locations 030H and 031 H, except that
quick-pulse programming are shown in disabled. However, the other lock bit P3.6 and P3.7 need to be pulled to a
Figures 13 and 14. Figure 15 shows the can still be programmed. logic low. The values are:
circuit configuration for normal program
memory verification. Note that the EA/vpp pin must not be al- (030H) - 15H indicates manufactured by
lowed to go above the maximum speci- Signetics
QUICK-PULSE PROGRAMMING fied Vpp level for any amount of time. (031 H) - 92H indicates SC87C51
The setup for microcontroller quick-pulse Even a narrow glitch above that voltage
programming is shown in Figure 13. Note can cause permanent damage to the de- ProgramNerify Algorithms
that the SC87C51 is running with a 4 to vice. The Vpp source should be well reg- Any algorithm in agreement with the
6MHz oscillator. The reason the oscilla- ulated and free of glitches and over- conditions listed in Table 2, and which
tor needs to be running is that the de- shoot. satisfies the timing specifications, is suit-
vice is executing internal address and able.
program data transfers. Program Verification
If lock bit 2 has not been programmed,
The address of the EPROM location to the on-chip program memory can be
be programmed is applied to ports 1 and read out for program verification. The
2, as shown in Figure 13. The code byte address of the program memory locations
to be programmed into that location is to be read is applied to ports 1 and 2 as '"Trademark phrase of Intel Corp.
February 1989 1-141

Erasure Characteristics The recommended erasure procedure is

Erasure of the EPROM begins to occur exposure to ultraviolet light (at 2537
when the chip is exposed to light with angstroms) to an integrated dose of at
wavelengths shorter than approximately least 15W-sec/cm2. Exposing the
4,000 angstroms. Since sunlight and flu- EPROM to an ultraviolet lamp of
orescent lighting have wavelengths in 12,00011W/cm2 rating for 20 to 39 min-
this range, exposure to these light utes, at a. distance of about 1 inch,
sources over an extended time (about 1 should be sufficient.
week in sunlight, or 3 years in room level
fluorescent lighting) could cause inadver- Erasure leaves the array in an all IS
tent erasure. For this and secondary ef- state.
fects, it is recommended that an
opaque label be placed over the win-
dow. For elevated temperature or sol-
vent environments, use Kapton tape
Fluorglas part number 2345-5 or equiv-
alent.
Table 2. EPROM Programming Modes
MODE RST PSEN ALE/PROG EA/vpp P2.7 P2.6 P3.7 P3.6

Program code data 1 0 O' Vpp 1 0 1 1
Pgm encryption table 1 0 O' Vpp 1 0 1 0
Pgm lock bit 1 1 0 O· Vpp 1 1 1 1
Pgm lock bit 2 1 0 O' Vpp 1 1 0 0
NOTES:
1. "0" - valid low for that pin, "1" - valid high for that pin.
2. Vpp = 12.75V ±O.25V.
3. Vee - 5V ±1 0% during programming and verification.
'ALE/PROG receives 25 programming pulses while Vpp is held at 12.75V. Each programming pulse is low for IOOILS (±IOILS) and
high for a minimum of lOlLS.
30
MAX
ACTIVE MODE
25
20
t
..: TYP(1)
E 15
ACTIVE MODE
0
2
10
5 f--++-I--+--I MAX
IDLE MODE
TYP(1)
~~==b::::J:::::1====~IDLEMODE
4MHz 8MHz 12MHz 16MHz
FREQ AT XTAL1

February 1989 1-142

Vee Vee
r-____-;Iee
Vee
~
Vee
Vee
RST
RST
(NC) XTAL2 (NC) XTAl2

CLOCK XTAl1 CLOCK XTAl1

O.45V
t CHCl
tClCX t ClCH
~-----tClCl--------~
tCLCH =tCHCL 5ns=
Vee
r-____-;Iee
Vee
!
Vee
RST
(NC) XTAl2
XTAl1
Vss

February 1989 1-143

+5V
AO-A? --_011 P1 PO 1\.---- PGM DATA
----01 RST EA/vpp 1 0 - - - - +12.75V
----tlP3.6 ALE/P'ROG 10---- ¥~ ~~~Su~~LSES
----tlP3.? SC87C51 Ps"EN 10----
...--_--1 XTAL2 P2.71o----
P2.61O----
P2.0 IJL--- A8-A11

-P2.3 I \ r - - - -
L--....-J.-I XTAL 1
Vss
1110.---------25 PULSES.----------o!
i-----
ALE/PROG: ~------------
, I
I
----.:....,
1"-. 10).lSMIN --I1---100).lS±10~
ALE/PROG: OL-I________~n n~ ___
Figure 14. PROG Waveform
February 1989 1-144

+5V
10K
Vee xS
AO-A7 _ _-,/1 P1 PO 1-_"':"''; PGM DATA
_ _ _-ojRST EA/Vpp i t - - - -
----tlP3.6 ALE/PROG i t - - - -
SC87C51
- - - - t l P3 .7 PSENIo----
,---.....---1 XTAL2 P2.71o---- 0 (ENABLE)
P2.6it----
P2.0 11'---- AS-A11

-P2.3 I \ r - - - -
-I--I XTAL 1
L - _......
Vss
Figure 15. Program Verification
EPROM PROGRAMMING AND VERIFICATION CHARACTERISTICS TA - 21°C to +27°C, VCC - 5V±1 0%, VSS - OV (see Figure 16)
SYMBOL PARAMETER MIN MAX UNIT

Vpp Programming supply voltage 12.5 13.0 V
Ipp Programming supply current 50 mA
1/tCLCL Oscillator frequency 4 6 MHz
tAVGL Address setup to PROG low 48tCLCL

tGHAX Address hold after PROG 48tCLCL
tDVGL Data setup to PROG low 48tCLCL
tGHDX Data hold after PROG 48tCLCL
tEHSH P2.7 (ENABLE) high to Vpp 48tCLCL
tSHGL Vpp setup to PROG low 10 ).IS
tGHSL Vpp hold after PROG 10 ).IS
tGLGH PROG width 90 110 ).IS
tAVQV Address to data valid 48tCLCL

tELQV ENABLE low to data valid 48tCLCL
tEHQZ Data float after ENABLE 0 48tCLCL
tGHGL PROG high to PROG low 10 ).IS
February 1989 1-145

PROGRAMMING" VERIFICATIOW
Pl.0-Pl.7 ADDRESS ADDRESS
\.
P2.0-P2.3 /
-4 I-- I AVOV
PORTO DATA IN DATA OUT

I DVGL I GHDX
I- I- I-
--
-4
I AVGL I GHAX
I-- , 25 PULSES "
ALE/PROG
IGLGH-t
I SHGL
Q:-:' 10- I GHGL
f----t I GHSL
V
EAlVpp ~
- - -- - - - - - - - - - - -
I EHSH
""
LOGIC 0
LOGIC 1 LOGIC 1
- - - - - - - - -
I EHOZ
P2.7
IELOr I-
EANBLE -./ I
"FOR PROGRAMMING VERIFICATION SEE FIGURE 13.

FOR VERIFICATION CONDITIONS SEE FIGURE 15.
Figure 16. EPROM Programming and Verification
February 1989 1-146

Signetics Section 2
8051 Family Derivatives
INDEX
8032/8052 Overview. . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-1
Differences from the 8051 .................................. 2-1
Program Memory ........................................ 2-1
Special Function Registers '" . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-1
Timer/Counters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-1
Serial Port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-2
Special Function Registers Table ............................ 2-5
Timer/Counter 2 Set-Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-8
Interrupts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-8
Port Structures .......................................... 2-9
SCN8032AH/SCN8052AH Data Sheet ........................ 2-11
8XC451 Overview ........................................ 2-1 8
Differences from the 8051 ................................. 2-18
Special Function Registers . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . .. 2-18
I/O Port Structure ....................................... 2-18
Processor Bus Interface .................................. 2-19
Standard Quasi-BidirectionalliO Port ....................... 2-19
Parallel Printer Port. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-19
Special Function Registers Table ........................... 2-20
SC80C451/SC83C451 Data Sheet ............................ 2-21
SC87C451 Data Sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-35
8XC552 Overview ........................................ 2-53
Differences from the 8051 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-53
Program Memory ....................................... 2-53
Data Memory. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-53
Special Function Registers ........ . . . . . . . . . . . . . . . . . . . . . . .. 2-53
Timer T2 .............................................. 2-53
Special Function Registers Table ........................... 2-55
Timer T3. the Watchdog Timer ... . . . . . . . . . . . . . . . . . . . . . . . . .. 2-59
Serial I/O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .............. 2-61
Reset Circuitry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-95
Interrupts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-96
1/0 Port Structure ....................................... 2-98
Port 1 Operation ........................................ 2-99
Port 5 Operation ....................................... 2-100
Pulse Width Modulated Outputs .. " ....................... 2-100
Analog-to-Digital Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-101
Power Reduction Modes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-105
Memory Organization ................................... 2-106
S83C552/S80C552 Data Sheet ............................. 2-112
8XC652 Overview ....................................... 2-123
Differences from the 80C51 .............................. 2-123
Special Function Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-123
Special Function Registers Table ...... " .................. 2-124
12C Serial Communications - SI01 ......................... 2-124
Idle and Power-Down Operation .......................... 2-124
Interrupt System ....................................... 2-125
Microcontroller Users' Guide
INDEX (Continued)
S83C6521S80C652 Data Sheet ................................... 2-127

8XC751 OVerview ............................................. 2-137
Differences from the 80C51 .................................... 2-137
Memory organization ......................................... 2-137
Special Function Registers ..................................... 2-137
Data Pointer (DPTR) .......................................... 2-138
I/O Port Latches (PO, P1, P3) ................................... 2-138
I/O Port Structure ............................................ 2-138
Special Function Registers Table ................................ 2-139
Timer/Counter ........................... ' ................... 2-139
12C Serial Interface ........................................... 2-140
S83C751 Data Sheet ........................................... 2-144
587C751 Data Sheet ........................................... 2-151
8XC752 Overview ............................................. 2-162
Idle Mode .................................................. 2-162
Power-Down Mode .......................................... 2-162
Memory Organization ......................................... 2-162
I/O Ports ................................................... 2-162
Special Function Registers Table ................................ 2-163
PWM Outputs ............................................... 2-163
AID Converter ............................................... 2-164
Countermmer ............................................... 2-165
12C Serial 110 .................................... , ......... , . 2-165
Interrupts ................................................... 2-165
Power-Down and Idle Modes ................................... 2-166
Instruction Set ............................................... 2-166
Special Function Registers ..................................... 2-167
Data Pointer ................................................ 2-167
Ports 0, 1, 2 ................................................ 2-167
87C752 Data Sheet ............................................ 2-168
Section 2
8051 FAMILY DERIVATIVES
The data memory organization is identical to the 8051
8032/8052 OVERVIEW except that the 8052 has an additional 128 bytes of RAM
overlapped with the special function register space. This
The 8052/8032 are identical to the 805118031 respec-
additional RAM is addressed using indirect addressing
tively except for added features. The 8052/8032 has:
only and is available as stack space. The 8052 data
8K ROM (8052 only) memory space is shown in Figure 2.
256 bytes RAM
SPECIAL FUNCTION REGISTERS
Counter/timer 2
The special function register space is the same as the
As a result, there are some additions to the interrupt
8051 except that the 8052 contains the additional special
structure, I/O pin alternate functions, and baud rate
function registers TICON, RCAP2L, RCAP2H, TL2 and
generation for the serial channel.
1H2. Since the standard 8051 on-chip functions are
Since the similarity is so close, only the additional fea- identical in the 8052, the SFR locations, bit locations
tures of the 8052/8032 are described. Where necessary, and operation are likewise identical. The only exceptions
some repetition of 8051 information will be made for the are in the interrupt mode and interrupt priority SFR's
sake of clarity. The 8052 is pin for pin and fully code (see Table 1).
compatible with the 8051.
TIMER/COUNTERS
DIFFERENCES FROM THE 8051 In addition to timer/counters 0 and 1 of the 8051 the
8052 contains timer/counter 2. Like timers 0 and l,'tim-
PROGRAM MEMORY
er 2 can operate as either an event timer or as an event
The data and program memory are organized virtually counter. This is selected by bit C/TI in the special func-
identically to the 8051. The 8052 ~sesses 8K bytes of tion register TICON (see Figure 3). It has three operat-
on-chip program memory. When EA is high, the 8052 ing modes:capture, auto-load, and baud rate generator,
fetches instructions from the internal ROM unless the which are selected by bits in the TICON as shown in
address exceeds 1FFFH. Locations 2000H to FFFFH are Table 2.
fetched from external program memory. When EA is
held low all instruction fetches are from external mem- In the Capture Mode there are two options which are se-
ory. The program memory space is shown in Figure 1. lected by bit EXEN2 in TICON. If EXEN2 = 0, then
Timer 2 is a 16-bit timer or counter which upon over-
FFFF , . . . . - - - - - - - - - - FFFF , . . - - - - - - - - - - .
11K
BYTES
EXTERNAL
14K
--OR-_.... BYTES
EXTERNAL
.. ~-------~
AND
:::1~_______~__ 8YTE8_NA
__L______ ~ GOOD ~_ _ _ _ _ _ _.....J
Figure 1. 8052 Program Memory
February 1989 2-1

Section 2 - 8051 Derivatives 8032/8052
INTERNAL
FFFF r-----------,
INDIRECT
f
ADDRESSING ONLY
8OHTOFFH
FF/
FFr-~--------~
14K
SFRa BYTES
DIRECT
ADDRESSING
ONLY
-- EXTERNAL
--AND~
80
7F~------------------~
DIRECT ..
INDIRECT
ADDRESSING
oo~------------~ oooo~---------------~
Figure 2. 8052 Data Memory
flowing sets bit TF2, the Timer 2 overflow bit, which can Figure 3). Note that the baud rate for transmit and re-
be used to generate an interrupt. If EXEN2 = 1, then ceive can be simultaneously different. Setting RCLK
Timer 2 still does the above, but with the added feature and/or TCLK puts Timer 2 into its baud rate generator
that a 1-to-O transition at external input TIEX causes mode, as shown in Figure 6.
the current value iu the Timer 2 registers, 1L2 and TH2
to be captured into registers RCAP2L and RCAP2H, re- The baud rate generator mode is similar to the auto-
spectively. (RCAP2L and RCAP2H are new Special reload mode, in that a rollover in TH2 causes the Timer
Function Registers in the 8052.) In addition, the transi- 2 registers to be reloaded with the 16-bit value in regis-
tion at TIEX causes bit EXF2 in TICON to be set, and ters RCAP2H and RCAP2L, which are preset by soft-
EXF2 like TF2, can generate an interrupt. The Capture ware.
Mode is illustrated in Figure 4.
Now, the baud rates in Modes 1 and 3 are determined by
In the auto-reload mode there are again two options, Timer 2's overflow rate as follows:
which are selected by bit EXEN2 in TICON. If EXEN2
= 0, then when Timer 2 rolls over it not only sets TF2 Timer 2 Overflow Rate
but also causes the Timer 2 registers to be reloaded with Modes 1, 3 Baud Rate = ---------
the 16-bit value in registers RCAP2L and RCAP2H, 16
which are preset by software. If EXEN2 = 1, then Timer The Timer can be configured for either "timer" or
2 still does the above, but with the added feature that a "counter" operation. In the most typical applications, it
1-to-0 transition at external input TIEX will also trigger is configured for "timer" operation (C/TI = 0). "Timer"
the 16-bit reload and set EXF2. The auto-reload mode operation is a little different for Timer 2 when it's being
is illustrated in Figure 5. used as a baud rate generator. Normally, as a timer it
would increment every machine cycle (thus at 1112 the
The baud rate generation mode is selected by RCLK = 1 oscillator frequency). As a baud rate generator, however,
and/or TCLK = 1. It will be described in conjunction it increments every state time (thus at 112 the oscillator
with the serial port. frequency). In that case the baud rate is given by the
formula
SERIAL PORT
The serial port of the 8052/8032 is identical to that of Modes 1,3 Oscillator Frequency
the 8051 except that counter/timer 2 can be used to Baud Rate = -------------
generate baud rates. 32x [65536 - (RCAP2H, RCA2L)]
In the 8052, Timer 2 is selected as the baud rate gen- where (RCAP2H, RCAP2L) is the content of RCAP2H
erator by setting TCLK and/or RCLK in TICON (see and RCAP2L taken as a 16-bit unsigned integer.
February 1989 2-2

(MSB) (LSB)
TF2 EXF2 RCLK TCLK EXEN2 TR2 c/f2 cMu:2 !-
Symbol Poalllon Name and SlgnllfC8nce
TF2 T2CON.7 TImer 2 overflow flag set by a TImer 2 overflow and must be cleared by software.
TF2 will not be set when efther RCLK = 1 or TCLK = 1.
EXF2 T2CON.6 TImer 2 external flag set when either a capture or reload is caused by a negative
transition on T2EX and EXEN2 = 1. When TImer 2 interrupt is enabled. EXF2 = 1
will cause the CPU to vector to the TImer 2 Interrupt routine. EXF2 must be
cleared by software.
RCLK T2CON.5 Receive clock flag. When set, causes the serial port to use Timer 2 overflow
pulses for Its receive clock in Modes 1 and 3. RCLK = 0 causes Timer 1 overflow
to be used for the receive clock.
TCLK T2CON.4 Transm" clock flag. When set, causes the serial port to use Timer 2 overflow
pulses for its transmit clock in modes 1 and 3. TCLK = 0 causes Timer 1
overflows to be used for the transmit clock.
EXEN2 T2CON.3 Timer 2 external enable flag. When set, allows a capture or reload to occur as a
result of a negative transition on T2EX if TImer 2 Is not being used to clock the
serial port. EXEN2 = 0 causes Timer 2 to ignore events at T2EX.
TR2 T2CON.2 Startlstop control for TImer 2. A logic 1 starts the timer.
c/f2 T2CON.l Timer or counter select. (Timer 2)
o = Internal timer (OSC/12)
1 = External event counter (faUing edge triggered).
CP/m T2CON.O Capture/Reload flag. When set, captures will occur on negative transitions at
T2EX if EXEN2 = 1. When cleared, auto-reloads will occur either with Timer 2
overflows or negative transitions at T2EX when EXEN2 = 1. When either RCLK
= 1 or TCLK = I, this bit is Ignored and the timer is forced to auto-reload on
Timer 2 overflow.
Figure 3. Timer/Counter 2 (T2CON) Control Register
nMER2
INTERRUPT
EXEN2
Figure 4. Timer 2 in Capture Mode
February 1989 2-3

TIMER 2
INTERRUPT
EXEN2
Figure 5. Timer 2 in Auto-Reload Mode
nMER1
OVEIIFUlW
RX CLOCK
TX CLOCK
.x....
L NOTa AYAUlUUTY OF ADDI110NAL IX11!RNAL INTEARUPT
Figure 6. Timer 2 in Baud Rate Generator MOde
February 1989 2-4

Table 1. Special Function Registers

Direct Bit Address, Symbol or Alternative Port Function Reset Value
Symbol Description
Address MSB LSB
ACC' Accumulator EOH E7 E6 E5 E4 E3 E2 E1 EO OOH
B* B register FOH F7 F6 F5 F4 F3 F2 F1 FO OOH
DPTR: Data pointer (2 bytes)
DPH Data pointer high 83H OOH
DPL Data pointer low 82H OOH
AF AE AD AC AB AA A9 A8
IE' Interrupt enable A8H EA I - I ET2 I ES I ETl I EXI I ETO I EXO OxOOOOOOB
BF BE BD BC BB BA B9 B8
IP' Interrupt priority B8H -
I - I PT2 I PS I PTl I PX1 I PTO I PXO xxOOOOOOB
87 86 85 84 83 82 81 80
PO' Port 0 80H AD7 I AD6 I AD5 LAD4 J AD3 J AD2 1 AD1 LADO FFH
97 96 95 94 93 92 91 90
Pl' Port 1 90H -
I -
I -
I -
I -
I - IT2EXI T2 FFH
A7 A6 A5 A4 A3 A2 Al AO
P2' Port 2 AOH A15 I A14 I A13 I A12 I All I AlO I A9 I A8 FFH
B7 B6 B5 B4 B3 B2 B1 BO
P3' Port 3 BOH FFH
RD IWR ITO I Tl I INTil INTO I TxD I RxD
PC ON Power control 87H SMODI - I - I - I GF1 I GFO I PD I IDL OxxxxxxxB
D7 D6 D5 D4 D3 D2 D1 DO
PSW* Program status word DOH CY I AC I FO I RS1 I RSO I OV I - I P OOH
RCAP2H# Capture high CBH OOH
RCAP2L# Capture low CAR OOH
SBUF Serial data buffer 99H xxxxxxxxB
9F 9E 9D 9C 9B 9A 99 98
SCON' Serial controller 98H SMO I SM1 I SM2 I REN I TB8 I RB8 I TI I RI OOH
SP Stack pointer 81H 07H
8F 8E 8D 8C 8B 8A 89 88
TCON* Timer control 88H TF1 I TR1 I TFO I TRO I lEI I ITl I lEO I ITO OOH
CF CE CD CC CB CA C9 C8
T2CON*# Timer 2 control C8H TF2 I EXF21RCLK ITCLK I E)CEN2 1 TR2 I C/T21 CP/RL2 OOH
THO Timer high 0 8CH OOH
TH1 Timer high 1 8DH OOH
TH2# Timer high 2 CDH OOH
TLO Timer low 0 8AH OOH
TLl Timer low 1 8BH OOH
TL2# Timer low 2 CCH OOH
TMOD Timer mode 89H GATE I CIT I M1 I MO IGATE I CIT I M1 I MO OOH
* ~ BIt addressable
# ~ SFRs are modified from or added to the 80C51 Timer 2 as a baud rate generator is shown in Figure 6.
SFRs. This Figure is valid only if RCLK + TCLK ~ 1 in
TICON. Note that a rollover in TH2 does not set TF2,
Table 2. Timer 2 Operating Modes and will not generate an interrupt. Therefore, the Timer
2 interrupt does not have to be disabled when Timer 2 is
RCLK + TCLK CP/RL2 TR2 Mode in the baud rate generator mode. Note too, that if
0 0 1 16-bit Auto-reload EXEN2 is set, a 1-to-0 transition in TIEX will set EXF2
0 1 1 16-bit Capture but will not cause a reload from (RCAP2H, RCAP2L) to
1 X 1 Baud rate generator (TH2, TL2). Thus when Timer 2 is in use as a baud rate
X X 0 (off) generator, TIEX can be used as an extra external inter-
rupt, if desired.
February 1989 2-5

Section 2 8051 - Derivatives 8032/8052

It should be noted that when Timer 2 is running (1m = not be written to, because a write might overlap a reload
1) in "timer" function in the baud rate generator mode, and cause write and/or reload errors. Turn the Timer off
one should not try to read or· write 1H2 or 1L2. Under (clear 1m) before accessing the Timer 2 or RCAP reg-
these conditions the Timer is being incremented every isters, in this case.
state time, and the results of a read or write may not be
accurate. The RCAP registers may be read, but should The serial port in Modes 1 and 3 with the timer 2 baud
rate interface is shown in Figures 7 and 8.
TIMER2
OVERFLOW
WRITE
SBUF
TO --~r--=~~~~~~--~~~--~----r-~ ~r-~ __ Txe
Rxe
TRANSMIT
I
716 RESET
RECEIVE
R;~ux: !l!TAAT IITI
.T DETECTOR SAMPlE TIMEI

181 ., D> OJ .. bi I DI I D1 I STOP81T
~SH~I~FT~________~L_ _ _ _JL-__- L__~____~__-L___ .~
~R~I ______________________________________________________ Jr----
Figure 7. Serial Port Mode 1 in the 8052
February 1989 2-6

Section 2 8051 - Derivatives 8032/8052
TIMER 1 TIMER 2
OVERFLOW OVERFLOW
__
WRITE
TO
SBUF ~-,~-::::£~~;r~--~=-----~---r~L- ~~ TXO
TCLK-
TI
TX
FLOCK! R
• WRITE TO SBUF L--JIL--__-"-__- - '____A-__...Jl.__.-.JL-__-'-___
- - - - , ftiiI!j I
DATA C S1P1 I I
SHIFT R D L-L-J L-n TRANSMIT
fij)\STA.T .tTi 00' Ll!i::X::Q.L1 D3 ~~ru;;;;::;,:::S:T:::O:::P:::B;IT;==
TI I
RXD BIT DETECTORI orA.T on I DO

RECEIVE
1 SHIFT
SAMPLE TIMES
--L-__~~__JL____IL___~____~__~L____L____L____A_____
__________________________________________________________r____
~
R
I
~
Figure 8. Serial Port Mode 3 in the 8052
February 1989 2-7


TIMER/COUNTER 2 SET-UP
Except for the baud rate generator mode, the values giv-
en for 1'2CON do not include the setting of the TR2 bit.
Therefore, bit TR2 must be set, separately, to turn the
Timer on. See table 3 for set-up of timer 2 as a timer.
See table 4 for set-up of timer 2 as a counter.
Table 3. Timer 2 as a Timer

T2CON
Mode Internal External
Control Control
(Note 1) (Note 2) wo------__________
16-bit Auto-Reload OOH 08H
16-bit Capture 01H 09H
Baud rate generator receive and
transmit same baud rate 34H 36H INTERRUPT
SOUACEI
Receive only 24H 26H
Transmit only 14H 16H
Table 4. Timer 2 as a Couuter ",------------------

TMOD
Mode Iuternal Control External Control
(Note 1) (Note 2)
16-bit 02H OAH
Auto-Reload 03H OBH
NOTES:
1. Capture/reload occurs only on timer/counter overflow.
2. Capture/reload occurs on timer/counter overflow and
a 1 to 0 transition on 1'2EX (PI. 1) pin except when
timer 2 is used in the baud rate generator mode.
USING TIMER/COUNTER 2
TO GENERATE BAUD RATES
For this purpose, Timer 2 must be used in the baud rate Figure 9. 805218032 Interrupt Sources
generating mode. If Timer 2 is being clocked through
pin 1'2 (P1.0) the baud rate is: The Interrupt Enable Register and the Interrupt Priority
Register are modified to include the additional 8052 in-
Timer 2 Overflow Rate terrupt sources. The operation of these registers is iden-
Baud Rate = --------- tical to the 8051. The registers are detailed in Figures
16 10, 11 and 12.
And if it is being clocked internally the baud rate is: In the 8052, the Timer 2 Interrupt is generated by the
logical OR of TF2 and EXF2. Neither of these flags is
Osc Freq cleared by hardware when the service routine is vectored
Baud Rate = to. In fact, the service routine may have to determine
32 x [65536 - (RCAP2H, RCAP2L)] whether it was TF2 or EXF2 that generated the inter-
rupt, and the bit will have to be cleared in software.
To obtain the reload value for RCAP2H and RCAP2L All of the bits that generate interrupts can be set or
the above equation can be rewritten as: cleared by software, with the same result as though it
had been set or cleared by hardware. That is, interrupts
Osc Freq can be generated or pending interrupts can be canceled
RCAP2H, RCAP2L = 65536 - - - - - - in software.
32 x Baud Rate
The interrupt vector addresses and the interrupt priority
INTERRUPTS for requests in the same priority level are given in the
The 8052 has 6 interrupt sources as shown in Figure 9. following:
All except TF2 and EXF2 are identical sources to those
in the 8051.
February 1989 2-8

Section 2 8032/8052
HIGH PRIORITY
IP REGISTER INTERRUPT
~~--~~4---~
I
I
I
~c>f~~---I....j
TFO,-------~~~
INTERRUPT
POLLING
I SEQUENCE
I
I
~
II >J~H---++I
I
I
TFl-------+t--o' ~I ~-ro-~-4+I
I
I
I
>----...--<Y ~e>j---r-~....J---I-~
RI
TI
TF2
EXF2
INDIVIDUAL GLOBAL LOW PRIORITY

ENABLES DISABLE INTERRUPT
Figure 10. 8052 Intermpt Control System
Source Vector Address Priority WithIn

Level
1. IEO 0003H (highest)
2. TFO OOOBH
3. IEI 0013H
4. TFI OOlBH
5. RI + TI 0023H
6. TF2 + EXF2 002BH (lowest)
Note that they are identical to those in the 8051 except

for the addition of the Timer 2 (TF1 and EXF2) inter-
rupt at 002BH and at the lowest priority within a level.
PORT STRUCTURES
The port structures are identical in both parts, except

that on the 8052/8032 ports P1.0 and P1.1 include the
Timer 2 alternate functions as follows:
PLO T2 (Timer/counter 2 external input)

Pl.l T2EX (Timer/counter 2 capture/reload trigger)
As with the 8051, these alternate functions can only be

activated if the corresponding bit latch in the port SFR
contains a 1.
February 1989 2-9

(MSB) (LSB) (MSB) (LSB)

I EA IxlmIEsIET1IEXlIETOIEXO I x IxlPT2lpslpT1lpXllPTOI PXO I
Symbol Po8ItIon Function Symbol PGlllllon Function
EA IE.7 disablaa all Interrupts. If EA = 0, no IP.7 reserved
Inlerrupt will be acknowledged. If EA - 1,
each Interrupt source is Individually IP.6 reserved
enabled or dI8abIad by setting or clearing PT2 IP.5 defines the Timer 2 interrupt priority
Its enable bit. lavel. PT2 = 1 programs rt to the
IE.6 reserved. higher priority laval.
ET2 IE.S enables or disables the TImer 2 Overftow PS IP.4 defines the Serial Port interrupt priority
or capture interrupt. If ET2 = 0, the TImer laval. PS = 1 programs It to the
2 Interrupt Is cfosabled. higher priority laval.
ES IE.4 • enables or disables the SerIal Port
Interrupt. If ES = 0, the Serial Port
PT1 IP.3 defines the Timer 1 interrupt priority
laval. PT1 = 1 programs It to the
Interrupt Is disabled. higher priority laval.
ETl IE.3 enables or disables the Timer 1 Overflow PXl IP.2 defines the Extarnallnterrupt 1 priority
i$rrupt. If ETl = 0, the TImer 1 Interrupt
level. PXl = 1 programs It to the
is disabled.
higher priority laval.
EXl IE.2 enables or disables External Interrupt 1. If
EXl = 0, Extarnallnterrupt 1 Is disabled. PTO IP.l defines the TImer 0 interrupt priority
ETO IE.l enables or disables the nner 0 Overflow laval. PTO = 1 programs It to the
higher priority lavel.
Interrupt. If ETO = 0, the TImer 0 Interrupt
isdiaablad. PXO IP.O defines the Extarnallnterrupt 0 priority
EXO IE.O enables or disables Extamallnterrupt O. If level. PXO = 1 programs It to the
EXQ = 0, ExternaIlntarrupt 0 18 disabled. higher priority level.
Figure 11. 8052 Interrupt Enable (IE) Register Figure 12. 8052 Interrupt Priority (IP) Register
February 1989 2-10

Signetics SCN8032AH/SCN8052AH

The Signetics SCNB032AH/SCNB052AH • SCN8032AH - control-oriented
is a high-performance microcontroller CPU with RAM and I/O
fabricated using the Signetics highly reli- T2/P1.0'1 40 Vee
able +5V, depletion-load, N -channel, sili-
• SCN8052AH - an SCN8032AH
with factory mask-program- T2EX/P1.1 ~ ~ PO.O/ADO
con-gate, N500 MOS process technol- P1.2~ 38 PO.1/AD1
mable ROM
ogy. It provides the hardware features,
• 8K X 8 ROM (SCN8052AH only) P1.3~ ~ PO.2/AD2
architectural enhancements and instruc-
.256 X 8 RAM P1.4~ ~ PO.3/AD3
tions that are necessary to make it a
powerful and cost-€ffective controller for
applications requiring up to 64K bytes of
• 32 I/O lines (four 8-bit ports)
• Three 16-bit timer/counters :~::~ ~ :~::~~~:
programming memory and up to 64K • Programmable full-duplex serial P1.7~ ~ PO.6/AD6
bytes of data storage. channel RST f2. ~ PO.7/AD7
- Variable transmit/receive RxD/P3.0~ DIP 31 EA
The SCNB032AH contains 256 bytes of
read/write data memory, 32 I/O lines baud rate capability ~/P3.1 ~ ~ ALE
configured as four B-bit ports, three 16- • Timer 2 capture capability ~/P3.2~ ~ PSEN
bit timer/counters, a six-$ource two- • External memory addressing INT1/P3.3~ ~ P2.7/A15
priority-level nested interrupt structure, a - 64K ROM and 64K RAM TO/P3.4~ ~ P2.6/A14
programmable serial I/O port and an on- • Boolean processor ..!!./P3.5~ ~ P2.5/A13
chip oscillator and clock circuitry. The • 128 user bit-addressable ~/P3.6~ ~ P2.4/A12
SCNB052AH has all of these features locations RD/P3.7g ~ P2.3/A11
plus BK bytes of non-volatile read-only • Upward compatible with
program memory. Both microcontrollers XTAL2~ ~ P2.2/A10
SCN8031 AH/SCN8051 AH XTAL1 ~ ~ P2.1/A9
ha ve memory expansion capabilities of
up to 64K bytes of data storage and 64K Vss.gg ~ P2.0/ A8
bytes of program memory that may be
LOGIC SYMBOL TOP VIEW
realized with standard TTL compatible
INDEX
memories. CORNER 6 1 40
8'"
Because of its extensive BCD/binary
~
rr-
arithmetic and bit-handling facilities, the
~
SCNB032AH/SCNB052AH microcontrol- PLCC
ler is efficient at both computational and -~
~= ~
control-oriented tasks. Efficient use of 17 29
program memory is also achieved by us-
ing the familiar compact instruction set ~-l:! 18 28
of the B031/B051. Forty-four percent of ....

-:5
TOP VIEW
Function Pin Function
t~.
the instructions are one-byte, 41 % two- Pin
byte, and 15% three-byte instructions. 1 NC 23 NC
2 T2/P1.0 24 P2.0/AS
With a 12MHz crystal, the majority of EA 3 T2EX/P1.1 25 P2.1/A9
the instructions execute in just 1.0j.lS. PSEN 4 P1.2 26 P2.2/A10
The longest instructions, multiply and di- ALE 5 P1.3 27 P2.3/A11
~t~-
-T2 6 P1.4 28 P2.4/A12
vide, require only 4j.1S at 12MHz. P1.5 P2.5/A13
7 29
]~li
~ '~-~ 8 P1.6 30 P2.6/A14
::>mrn- .., 9 P1.7 31 P2.7/A15
u..1RI'l-t;;: 10 RST 32 !5Srn
~ TO-~ 11 RxD/P3.0 33 ALE
<~- 12 NC 34 NC
!! - 13 TxD/P3.1 35 ~
8R!l-
....
en
14
15
iFlTO/P3.2
mTT/P3.3
36
37
PO.7/AD7
PO.6/AD6
16 TO/P3.4 38 PO.5/AD5
17 T1/P3.5 39 PO.4/AD4
18 WI1/P3.6 40 PO.3/AD3
19 R[)/P3.7 41 PO.2/AD2
22 Vss 44 Vee
February 1989 2-11


ROM~R:a==5ce:)HCCCICC ::L::
Temperature and Frequency
ROM less ROM Package
ROM Pattern No,
32 - Extl256 Applies to masked ROM versions
SCN8032HCCN40 SCN8052HCCN40 o to +70·C, plastiC DIP 3.5 to 12MHz
52 - 8K/256 only. Number will be assigned by SCNS032HCCA44 SCN8052HCCA44 o to + 70·C, plastic LCC 3.5 to 12MHz
Signetics. Contact Signetics sales
Power office for ROM pattern submission SCNS032HACN40 SCN8052HACN40 -40 to +85·C, plastic DIP 3.5 to 12MHz
Consumption requirements.
SCNS032HACA44 SCNS052HACA44 -40 to +S5·C, plastiC LCC 3.5 to 12MHz
H -P~:~~c:~ Pins
40 - 40-pin SCN8032HCFN40 SCNS052HCFN40 o to +70·C, plastic DIP 3.5 to 15MHz
44 - 44-pin SCNS032HCFA44 SCN8052HCFA44 o to + 70·C, plastic PLCC 3.5 to 15MHz
Package
A - Plastic LCC SCNS032HAFN40 SCNS052HAFN40 -40 to +85·C, plastic DIP 3.5 to 15MHz
I - Ceramic DIP
N - Plastic DIP SCN8032HAFA44 SCN8052HAFA44 -40 to +85·C, plastic PLCC 3.5 to 15MHz
Speed
C - 3.5 to 12MHz
F - 3.5 to 15MHz
A - -40·C to +85·C
C - O·C to +70·C
BLOCK DIAGRAM
--------l
PCON scaN TIoIOD TCON

T2CON THO TLO THI
TL, TH2 TL2 RCIIP2H
RCIIP2l SBUF IE IP
iiSEN ~_.r--"""-::;"I
ALE
EA
RST
PUH".7
February 1989 2-12


PIN DESCRIPTION
PIN NO.
MNEMONIC TYPE NAME AND FUNCTION
DIP LCC
Vee 40 44 I Power Supply: This is the power supply voltage for normal operation.
PO.0-PO.7 39-32 43-36 1/0 Port 0: Port 0 is an open-drain, bidirectional 1/0 port. Port 0 is also the multiplexed
ory. In this application, it uses strong internal pullups when emitting 1s. Port 0 also
outputs the code bytes during program verification.
P1.0-P1.7 1-8 2-9 1/0 Port 1: Port 1 is an 8-bit bidirectional 1/0 port with internal pull-ups. Pins P1.0 and
P1.1 also correspond to the special functions T2, timer 2 counter trigger input, and
T2EX, external input to timer 2. The output latch on these two special functions must
be programmed to one for that function to operate. Port 1 also receives the low-order
address byte during program verification.
1 2 T2 (P1.0): Timerlcounter 2 trigger input.

2 3 T2EX (P1.1): Timerlcounter 2 external count input.
P2.0-P2.7 21-28 24-31 1/0 Port 2: Port 2 is an 8-bit bidirectional 1/0 port with internal pUll-ups. Port 2 emits the
accesses to external data memory that use 16-bit addresses (MOVX @DPTR). During
accesses to external data memory that use 8-bit addresses (MOVX @Ri), port 2 emits
the contents of the P2 special function register.
P3.0-P3.7 10-17 11, 1/0 Port 3: Port 3 is an 8-bit bidirectional 1/0 port with internal pull ups. Port 3 is also used
13-19 for the special features listed below: .
14 16 I TO (p3.4): Timer 0 external input
15 17 I !!JP3.5): Timer 1 external input
16 18 o WR (P3.8): External data memory write strobe
17 19 o RD (P3.7): External data memory read strobe
the device. A small external pull-down resistor (= 8.2KQ) from RST to Vss permits
power-on reset when a capacitor (= 10!d) is also connected from this pin to Vee.
ALE 30 33 1/0 Address Latch Enable: Output pulse for latching the low byte of the address during an
one ALE pulse is skipped during each access to external data memory.
29 32 o Program Store Enable: The read strobe to external program memory. When the device
is executing code from externa.L.EJ:Qgram memory, PSEN is activated twice each
machine cycle, except that two PSEN activations are skipped during each access to
external data memory. PSEN Is not activated during fetches from internal program
memory.
31 35 I External Access Enable: EA must be externally held low to enable..!l!.e device to fetch
code from external program memory locations OOOOH and 1 FFFH. If EA is held high, the
address greater than 1 FFFH.
XTAL1 19 21 I Crystal 1: Input to the inverting oscillator amplifier and input to the internal clock
generator circuits.
XTAL2 18 20 o Crystal 2: Output from the inverting oscillator amplifier.
February 1989 2-13

OSCILLATOR CHARACTERISTICS To drive the device from an external RESET

XTAL1 and XTAL2 are the input and out- clock source, XTAL2 should be driven A reset is accomplished by holding the
put, respectively, of an inverting ampli- while XTAL1 should be grounded. There RST pin high for at least two machine
fier. The pins can be configured for use are no requirements on the duty cycle of cycles (24 oscillator periods), while the
as an on-chip oscillator, as shown in the the external clock signal, because the oscillator is running.
logic symbol, page 1. input to the internal clock circuitry is
through a divide-by-two flip-flop. How-
ever, minimum and maximum high and
low times specified in the data sheet
must be observed.
ABSOLUTE MAXIMUM RATINGS1. 2. 3

All voltages with respect to ground -0.5 to +7.0 V
Power dissipation 2.0 W
DC ELECTRICAL CHARACTERISTICS TA - O°C to +70°C , Vee - 5V ±10%, Vss - OV4, 5

Limits
Min Max
VIL Input low voltage -0.5 O.S V
VIH Input high voltage, except RST and XTAL2 2 Vee+0.5 V
VIH1 Input high voltage to RST for reset, XTAL2 XTAL1 to Vss 2.5 Vee+0.5 V
VOL Output low voltage, ports 1, 2, 3 6 IOL - 1.6mA 0.45 V
VOLl Output low voltage, port 0, ALE, PSEN6 IOL - 3.2mA 0.45 V
VOH Output high voltage, ports 1, 2, 3 IOH - -SOj.lA 2.4 V

VOH1 Output high voltage port 0 in external bus IOH - -400j.lA 2.4 V
mode, ALE, PSEN)3
IlL Logical 0 input current, ports 1, 2, 3 VIN - 0.45V -SOO j.lA
IIH1 Input high curent to RST for reset VIN - Vee - 1.5V 500 j.lA
III Input leakage current, port 0, EA 0.45 < VIN < Vee ±10 j.lA
IIL2 Logical 0 input current for XTAL2 XTAL1 - Vss, VIN - 0.45V -3.2 rnA
lee Power supply current All outputs disconnected 175 rnA
and EA - Vee
CIO Pin capacitance fe - 1MHz, TA - 25°C 10 pF
TA =-40°C to +85°C - Extended temperature range - SCNS052HAC only
VIH Input high voltage, except RST and XTAL2 2.2 Vee+0.5 V
VIHl Input high voltage to RST for reset, XTAL2 XTAL1 to VSS 2.7 V
lee Power supply current All outputs disconnected 175 rnA
and EA - Vee
NOTES:
2 For operating at elevated temperatures, the device must be derated based on +150 0 C maximum junction temperature.
charge. Nonetheless, it is suggested that conventional precautions be taken to avoid applying voltages greater than the ratee! maxima.
5. All voltage measurements are referenced to ground. For testing, all input signals swing between 0.45V and 2.4V with a transition time of
20ns maximum. All time measurements are referenced at input voltages of 0.8V and 2.0V and at output voltages of 0.8V and 2.0V as
appropriate.
6. VOL is degraded when the device rapidly discharges external capacitance. This AC noise is most pronounced during emission of address
data. When using external memory, locate the latch or buffer as close to the device as possible.
Emitting Degraded
Datum Ports I/O Lines VOL (Peak Max)
Address P2. PO Pl, P3 0.8V
Write Data PO P1, P3, ALE 0.8V
7. eL - 100pF for port 0, ALE and PSEN outputs; eL - 80pF for all other ports.
February 1989 2-14


Min Max Min Max
Pro!lram Memo
l/tCLCL Oscillator frequency: Speed Versions
SCN8052 C 3.5 12 MHz
SCN8052 F 3.5 15 MHz
tLHLL 1 ALE pulse width 127 2tCLCL 40 ns
tAvLL 1 Address valid to ALE low 43 tCLCL 40 ns
tLLAX 1 Address hold after ALE low 48 tCLCL-35 ns
tLLlV 1 ALE low to valid instruction in 233 4tCLCL -100 ns
tLLPL 1 ALE low to PSEN low 58 tel CI -25 ns
tpLPH 1 PSEN pulse width 215 3tCLCL-35 ns
tpLiV 1 PSEN low to valid instruction in 125 3tCLCL -125 ns
tPXIZ 1 Input instruction float after PSEN 63 tCLCL -20 ns
tAVIV 1 Address to valid instruction in 302 5tCLCL -115 ns
tpIA7 1 PSEN low to address float 20 20 ns
tpXAV 1 PSEN to address valid 75 tCLCL-8 ns
Data Memory
tRLRH 2 RD pulse width 400 6tCLCL -100 ns
tWLWH 3 WR pulse width 400 6tCLCL-100 ns
tRLDV 2 RD low to valid data in 252 5tCLCL -165 ns
tRHDX 2 Data hold after R 0 0 0 ns
tRHD7 2 Data float after RD 97 2tci CI -70 ns
tLLDV 2 ALE low to valid data in 517 8tCLCL-150 ns
tAVDV 2 Address to valid data in 585 9tCLCL -165 ns
tLLWL 2, 3 ALE low to RD or WR low 200 300 3tCLCL-50 3tCLCL+50 ns
tAVWL 2, 3 Address valid to WR low or RD low 203 4tcLCL -130 ns
tOVWX 3 Data valid to WR transition 23 tCLCL-60 ns
t()VW~ 3 Data vaid to WR high 433 7tCLCL-150 ns
tWHOX 3 Data hold after WR 33 tCLCL-8 ns
tRLAZ 2 RD low to address float 20 20 ns
External lock
tCHCX 5 High time 20 ns
tCLCX 5 Lr.w time 20 ns
tCLCH 5 Rise time 20 ns
tCHCL 5 Fall time 20 ns
Shift Register
tXLxL 4 Serial port clock cycle time 1.0 12tCLCL f.LS
tOVXH 4 Output data setup to clock rising edge 700 10tCLCL-133 ns
NOTES.

always '1' (- time). The other characters, depending on their R - RD signal
that Signal. The designations are: V - Valid
A - Address W -WR signal
o - I nput data Z - Float
H - Logic level high Examples: tAvLL - Time for address valid to ALE low.
I - I nstruction (program memory contents) tLLPL - Time for ALE low to PSEN low.
February 1989 2-15

ALE
~ _ _ _J
PORTO _ _ _ _~
1o---tAVIV-----.I
PORT 2 )< A8-A15 A8-A15
ALE "- /
J.-- WHLH
PsE"N
tLLDV
I--- t LLWL tRLRH
RD "- /
t AVLL
I---t foo- tLLAX-o
II--
io--tRLDv--o
tRLAZ
tRHDX ..... IF tRHDZ
PORTO ~ . _''')"
AO-A?
'" n" np, 1'1
tAVWL
DATA IN
»>K AO-A? FROM PCL INSTR IN
t AvDV
PORT 2 )< P2.0-P2.? OR A8-A 15 FROM DPH A8-A15 FROM PCH
ALE "- /
0-----0 tWHLH
ffiN
I---- t LLWL t WLWH
WR
tAVLL
i----<
I--tLLAX ""
"'
I-- tOVWX
/
Io--t t WHOX
tOVWH
PORTO~ . Fom ~g~~~ no, I> DATA OUT ~ AO-A? FROM PCL INSTR IN
tAVWL -
PORT 2 )< P2.0-P2.? OR A8-A15 FROM DPH A8-A15 FROM PCH
February 1989 2-16

ALE
tOVXH HI t XHOX
OUTPUT DATA
f
WRITE TO SBUF
,'----,J '---".J '-_---J ' - - - - ' '-_---J ' - - _ - ' '-_---J ~_.J
I INPUT DATAl _ _ _ _ _ _..1

1
CLEAR RI t
SET RI
Vee-O.5·-------- O.7Vce
0.45V
~---------tcLCL-----~
Vee-O.5
O.45V
=x O.2Vcc+O.9 >C
_..O_.2_V;.;;e.;;.e-...:O;,;.;.1~_ _
Timing
Reference
Points
<
for a logic H1 Hand O.4SV for a logic HOH. For timing purposes, a port Is no longer floating
a logic H1 H and V IL max for a logic ·0·.
the 10adedVOHlVOL level occurs.IOH/IOL~±20mA.

February 1989 2-17

Section 2 - 8051 Derivatives 8XC451
DIFFERENCES FROM THE 8051

8XC451 OVERVIEW
The SC80C4S1, the SC83C4S1, and the SC87C4S1 SPECIAL FUNCTION REGISTERS
(hereafter referred to collectively as the 83C4S1) are
The SFRs are identical to those of the standard 80CS1
I/O expanded versions of the 80CSl. Three I/O ports
with the exception of four registers that have been added
have been added to the basic 80CS1 architecture for a
to allow control of the three additional I/O ports P4 PS
and P6. The additional registers are P4, PS, P6,~ and
total of 7 on-chip I/O ports. The LCC version has a total
of 68 pins. The DIP version has 64 pins. Port 6 has 4
CSR. Registers P4, PS, and P6 function as port latches
control lines to facilitate high-speed asynchronous I/O
for ports 4, 5, and 6 respectively. These registers oper-
functions.
ate identically to those for ports 0 through 3 of the
The 83C451187C4S1 includes a 4K X 8 ROM/EPROM, a 80CSl.
128 X 8 RAM, 56 (LCC) or 52 (DIP) I/O lines, two 16-
The Control Status Register (CSR) is used to control the
bit timer/counters, a five source, two priority, level nest-
mode of operation of port 6 and indicates the current
ed interrupt structure, a serial I/O port for either full
status of port 6. All control status register bits can be
duplex UART, I/O expansion, or multiprocessor commu-
read and written by the CPU except bits 0 and 1, which
nications, and an on-chip oscillator and clock circuits.
are read only. A Reset writes ones to bits 2-7 and zeros
The 8OC4S1 includes all of the 83C4S1 features except
to bits 0 and 1. See Table 5 for the specific function of
the on-board 4K X 8 ROM.
each bit in the Control Status register.
The 83C4S1 has two software selectable modes of re-
The SFR addresses for the 83C451 are identical to those
duced activity for further power reduction: idle mode and
in the 80CS1 except for the additional registers P4, P5,
power-down mode. Idle mode freezes the CPU while al-
P6, and CSR. Table 6 lists the SFR addresses bit
lowing the RAM, timers, serial port, and interrupt sys-
names and addresses (where applicable), and reset'val-
tem to continue functioning. Power-down mode freezes
ues for the 83C4S1. Table 7 is a detailed expansion of
the oscillator, causing all other chip functions to be in-
the special function registers.
operative while maintaining the RAM contents.
110 PORT STRUCTURE
The 83C4S1 features include:
The 8XC4S1 has a total of seven parallel I/O ports. The
• 80C51 based architecture
first four ports, PO through P3, are identical in function
• 68-pin LCC and 64-pin DIP packages
to those present on the 80CS1 family. The added ports 4
• Seven 8-bit I/O ports (LCC Version)
and 5 are identical in function to port 1, that is, they are
• Six 8-bit ports and one 4-bit port (DIP version)
standard quasi-bidirectional ports with no alternate func-
• 4K X 8 ROM or EPROM
tions and the standard output drive characteristics. Note
.128 X 8 RAM
th~t on the 68-pin LCC packages, port 4 is an 8-bit port,
• Two 16-bit counter/timers
while on the 64-pin DIP packages, only the lower four
• Two external interrupts
bits of port 4 are available. Port 6 is a specialized 8-bit
• External memory addressing capability
bidirectional I/O port with internal pull ups. This special
- 64K ROM and 64K RAM
port can sink/source three LS TTL inputs and drive
• Low power consumption
CMOS inputs without external pullups. The flexibility of
- Idle Mode
this port facilitates high-speed parallel data communica-
- Power-down mode
tions. Port 6 operating modes are controlled by the port
Table S. Control Status Register (CSR)

Bit 7 I Bit 6 Bit 5 I Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
MB1 T MBO MA1 I MAO OBFC IOSM OBF ISF
Output Buffer
Input Data Output Buffer Input Buffer
BFLAG Mode Select AFLAG Mode Select Flag Clear
Strobe Mode Full-Flag Full Flag
Mode
0/0 - Logic 0 output"
011 - Logic 1 output"
0/0
0/1
- Logic 0 output
- Logic 1 output
0 - N~veO
edge of ODS
-
Positive
edge of IDS
0- Output
data buffer
0- Input
data buffer
110 - IBF output 1/0 - OBF output" empty empty
1/1 - PE input
(0 - Select)
1/1 - SEL input
(0 - Data)
1 - Positive 1 =_bpw level
edge of ODS of IDS 1 - Output 1 - Input .
(1 - Disable I/O) (1 - Control/status) data buffer full data buffer full
NOTE:
"Output-always mode: MB1 - 0, MA1 - 1, and MAO - O. In this mode, port 6 is always enabled for output ODS only clears
th.e OBF flag. .
February 1989 2-18

Table 6. Special Function Register Addresses
REGISTER ADDRESS BIT ADDRESS

Name Symbol Address MSB LSB
Port 4 P4 CO C7 C6 C5 C4 C3 C2 C1 CO
Port 5 P5 C8 CF CE CD CC CB CA C9 C8
Port 6 data P6 D8 DF DE DD DC DB DA D9 D8
Port 6 control status CSR E8 EF EE ED EC EB EA E9 E8
6 Control Status Register (CSR). Port 6 and 111e CSR STANDARD QUASI-BIDIRECTIONAL 110 PORT
are addressed at 111e Special Function Addresses shown
in Table 6. Port 6 can be used as a standard I/O port, To use port 6 as a common I/O port, all of 111e control
or in strobed modes of operation in conjunction wi111 111e pins should be tied to ground. On hardware reset, bits
four port 6 control lines listed below: 2-7 of 111e CSR are set to one. Wi111 111e control pins
grounded, 111e Port's operation and electrical characteris-
tics will be identical to port 1 on 111e 80C51. No fur111er
ODS Output data strobe (active low) software initialization is required.
IDS Input data strobe (active low)
BF1.AG Bidirectional I/O pin. Can be programmed PARALLEL PRINTER PORT
to output 111e Input Buffer Full flag (IBF),
input an active low Port Enable (PE) sig- The 83C451 has 111e capacity to permit all of 111e intelli-
nal, or output a high or low logic level. gent features of a common printer to be handled by a
AF1.AG Bidirectional I/O pin. Can be programmed single chip. The features of Port 6 allow a parallel port
to output 111e Output Buffer Full (OBF) to be designed wi111 only line driving and receiving chips
flag, input a register select signal (SEL), required as additional hardware. The onboard UART al-
or output a high or low logic level. lows RS232 interfacing wi111 only level shifting chips add-
ed. The 8-bit parallel ports 0 to 6 are ample to drive
Port 6 can be used in a number of different ways to fa- onboard control functions, even when ports are used for
cilitate data communication. It can be used as a proces- external memory access, interrupts, and o111er functions.
sor bus interface, as a standard quasi -bidirectional I/O The RAM addressing ability of ports 0 to 2 can be used
port, or as a parallel printer port (ei111er polled or in- to address up to 64K bytes of a hardware buffer/spooler.
terrupt driven).
In addition, ei111er end of a parallel interface can be im-
PROCESSOR BUS INTERFACE plemented using port 6, and 111e interfaces can be inter-
rupt driven or polled in ei111er case. For more detailed
Port 6 allows 111e use of an 83C451 as an element on a information on port 6 usage, refer to 111e application
microprocessor type bus. The host processor could be a notes contained in Section 3, entitled "80C451 Operation
general purpose MPU or 111e data bus of a microcon- of Port 6" and "256K Centronics Printer Buffer Using
troller like 111e 83C451 itself. Setting up 111e 83C451 as a 111e SC87C451 Microcontroller".
processor bus interface allows single or multiple
microcontrollers to be used on a bus as flexible periph-
eral processing elements. Applications can include:
keyboard scanners, serial I/O controllers, servo control-
lers, etc.
On reset, Port 6 is programmed correctly (111at is Spe-

cial Function registers CSR and P6) for use as a bus in-
terface. This prevents 111e interface from disrupting data
on 111e bus of a host processor during power-up.
February 1989 2-19

Table 7. 8X4S 1 Special Function Registers

Direct Bit Names and Addresses
Symbol Description LSB Reset Value
Address MSB
ACC* Accumulator EOH E7 E6 E5 E4 E3 E2 El EO OOH
B* B register FOH F7 F6 F5 F4 F3 F2 F1 FO OOH
EF EE ED EC EB EA E9 E8
CSR*# Port 6 command/status E8H MB1 I MBO I MAl I MAO IOBFC IIDSM I OBF I IBF FCH
DPTR: Data pointer (2 bytes):
DPH High byte 83H OOH
DPL Low byte 82H OOH
IP* Interrupt priority B8H - I - I - I PS I PT1 I PX1 I PTO I PXO xxxOOOOOB
IE* Interrupt enable A8H EA I - I - I ES I ETl I EX1 I ETO I EXO OxxOOOOOB
PO· Port 0 80H 87 B6 85 84 83 82 81 80 FFH
P1* Port 1 90H 97 96 95 94 93 92 91 90 FFH
P2* Port 2 AOH A7 A6 AS A4 A3 A2 A1 AO FFH
P3* Port 3 BOH B7 B6 B5 B4 B3 B2 B1 BO FFH
P4*# Port 4 COH C7 C6 C5 C4 C3 C2 C1 CO FFH
P5*# Port 5 C8H CF CE CD CC CB CA C9 C8 FFH
P6*# Port 6 D8H DF DE DD DC DB DA D9 D8 FFH
PCON Power control 87H SMOni - I - I - I GF1 I GFO I PD I IDL OxxxOOOOB
D7 D6 D5 D4 D3 D2 D1 DO
PSW* Program status word DOH CY I AC I FO I RS1 I RSO I OV I - I P OOH
SBUF Serial data buffer 99H xxxxxxxxB
9F 9E 9D 9C 9B 9A 99 98
SCON* Serial port control 98H SMO I SM1 I SM2 I REN I TB8 I RB8 I TI I RI OOH
8F 8E 8D 8C 8B 8A 89 88
TCON* Timer/counter control 88H TF1 I TRI I TFO I TRO I lEI I ITl I lEO I ITO OOH
TMOD Timer/counter mode 89H GATE I CIT I MI I MO IGATEI CIT I MI I MO OOH

THO Timer 0 high byte 8CH OOH
TH1 Timer 1 high byte 8DH OOH
TLO Timer 0 low byte 8AH OOH
TLl Timer I low byte 8BH OOH
*SFRs are bit addressable.
#SFRs are modified from or added to the 80C5I SFRs.
February 1989 2-20

Signetics SC80C451/SC83C451
Microcontroller
DESCRIPTION FEATURES PIN CONFIGURATIONS

The Signetics SCBOC451/SCB3C451 is • User programmable microcontrolier
an I/O expanded, single-chip micro- • SC80C51 based architecture
controller fabricated with Signetics high- • 88-pin LCC and 84-pin DIP EA" '64 ALE
packages:
density CMOS technology. Signetics
epitaxial substrate minimizes latch-up
- Seven 80bit I/O ports (LCC P2.0/AB ~ ~ PSEN
version) P2.1/A9 ~ ~ P6.7
sensitivity. - Six 80bit ports and one 40bit
port (DIP version)
P2.21 A10 t4 ~ P6.6
The SCBOC451/SCB3C451 is a functional P2.3/A11 ~ ~ P6.5
• Port 8 features:
extension of the SCBOC51 microcontrol- - 8 data pins P2.4/A12 ~ §I P6.4
ler with three additional I/O ports and - 4 control pins P2.5/A13 ~ ~ P6.3
four I/O control lines. The LCC version - Direct MPU bus interface
P2.6/A14~ ~ P6.2
has a total of 6B pins. Four control lines - Parallel printer interface
associated with port 6 facilitate high • On the microcontrolier P2.7/A15 ~ ~ P6.1
speed asynchronous I/O functions. - 4K X 8 ROM (SC83C451 only) PO.7/AD7 ~ ~ P6.0
- 128 X 8 RAM PO.61 AD6 ~ 54 AFLAG
The SCB3C451 includes a 4K X B ROM, - Two 180bit counter/timers
- Two external interrupts PO.5/AD5tl¥ ~ ~AG
a 12B X B RAM, 56 (LCC) or 52 (DIP)
• External memory addressing P0.41 AD4 1 ~ ~
I/O lines, two 16-bit timer/counters, a
five source, two priority level, nested in-
capability PO.3/AD3~ ~ ODS
- 84K ROM and 84K RAM PO.21 AD2 ~ 50 Vss
terrupt structure, a serial I/O port for ei-
~ ~ XTAL1
• Low power consumption:
ther a full duplex UART, I/O expansion, - Normal operation: less than PO.1/AD1
or multiprocessor communications, and 24mA at 5V, 12MHz PO.O/ADO ~ DIP ¢.g XTAL2
an on-chip oscillator and clock circuits. - Idle mode
- Power-down mode
Vee ~ J!Y P5.7
The SCBOC451 includes all the SC- P4.3~ ~ P5.6
B3C451 features except the on-board 4K
LOGIC SYMBOL P4.2~ ~ P5.5
X B ROM.
P4.1 ~ ~4 P5.4
The SC80C451/SCB3C451 has two soft- P4.0 g t!,3 P5.3
ware selectable modes of reduced activ- P1.og ~2 P5.2
ity for further power reduction: idle mode P1.1~ ~ P5.1
and power-down mode. Idle mode freez-
jiG P5.0 _
es the CPU while allowing the RAM, tim-
ers, serial port, and interrupt system to
I P1.2~
P1.3~
P1.4g
F!l P3.7/~
~ P3.6/WR
continue functioning. Power-down mode
freezes the oscillator, causing all other
chip functions to be inoperative while
I P1.5 ~
P1.6 ~
~ P3.5/T1
36 P3.4/TO
maintaining the RAM contents. P1.7~ ~ P3.3/1NT1
RST 31 ~ P3.2/INTO
P3.0/RxD ~ ~ P3.1/TxD
TOP VIEW
INDEX
'"""~M
26CJ44
27 43
TOP VIEW
See next page for LCC pin functions
F ebrua ry 1989 2-21

CMOS Single-Chip 8-Bit Microcontroller SC80C451/SC83C451

o-
1
ROM::.:r:: CCCC C
ROMless
3 - ROM
::c
1 ROM Pattern No.
Applies to masked ROM versions
only. Number will be assigned by
Sig netics. Contact Sig netics sales
ROMlesa
SC80C451CCN64
SC80C451CGN64
SC80C451CBN64
ROM
SC83C451CCN64
SC83C451CGN64
SC83C451CBN64
Temp8rature and Package
o to +7000 plastic DIP
office for ROM pattern submission
requirements.
SC80C451 CCA68 SC83C451 CCA68 o to +70°C plastic LGC
Pins
SC80C451 CGA68 SC83C451 CGA68 o to +70°C plastic LCC
64 - 64-pin DIP SC80C451 CBA68 SC83C451CBA68 o to +7000 plastic LCC
68 - 68-pln PLCC
SC80C451 ACN64 SC83C451ACN64 -40 to +85°C plastic DIP
Package
A - Plastic PLCC SC80C451AGN64 SC83C451AGN64 -40 to +8500 plastic DIP
N - Plastic DIP SC80C451 ACA68 SC83C451 ACA68 -40 to +85°C plastic LCC
Speed SC80C451 AGA68 SC83C451 AGA68 -40 to +8500 plastic LCC
B - 0.5 to 12MHz
C - 3.5 to 12MHz
G - 3.5 to 16MHz
A - _40°C to +85 0 C
C - OOC to +70 0 C
LCC PIN FUNCTIONS
INDEX
~tj 10
LCC
60
26 44
27 43
TOP VIEW
Pin Function Pin Function Pin Function
1 EA 24 P4.2 47 P5.3
2 P2.0/A8 25 P4.1 48 P5.4
3 P2.1/A9 26 P4.0 49 P5.5
4 P2.2/Al0 27 Pl.0 50 P5.6
5 P2.3/All 28 Pl.l 51 P5.7
6 P2.4/A12 29 Pl.2 52 XTAL2
7 P2.5/A13 30 Pl.3 53 XTALI
8 P2.6/A14 31 Pl.4 54
9
10
11
12
P2.7/A15
PO.7/AD7
PO.6/AD6
PO.5/AD5
32
33
34
35
Pl.5
Pl.6
Pl.7
55
56
57
I
BFLAG
RST 58 AFLAG
13 PO.4/AD4 36 P3.0/RxD 59 P6.0
14 PO.3/AD3 37 P3.1/TxD 60 P6.1
15 PO.2/AD2 38 P3.2/iFffii 61 P6.2
16 PO.l/ADl 39 P3.3/iNi'i 62 P6.3
17 PO.O/ADO 40 P3.4/TO 63 P6.4
18 Vcc 41 P3.5/Tl 64 P6.5
19 P4.7 42 P3.6/iNIi 65 P6.6
20 P4.6 43 P3.7/im 66 P6.7
21 P4.5 44 P5.0 67 PSEN
22 P4.4 45 P5.1 68 ALE
23 P4.3 46 P5.2
February 1989 2-22

~ m w
g- 6 o cO"
~
-<~
0
~
2
a~ ;
g.fh
co
00 )0
Q en~
_
~ en §
11
co
i: "0
i------Ttf[-F-'ieTiF------.~--:
c:
"0
00
.
!l
I
III
;::+
~
o·
a
(")
o
::J
~ II 11:-".:,.. ':
SBUF IE IP
I~=~I I I~
~:i:::1
RST~
n= li~~II!f
CONIROL 1t
U 11 if
~
~
1T
IT if
I~....-----.
~ DPTR ~ en
I o00
I o
oJ::o.
_____ J
l
-
....
01
en !l8.c:
o00
w
"0
w
""5l
o
oJ::o. =
0"
~
....
01 0"
:::l

PIN DESCRIPTION
PIN NO.
MNEMONIC DIP PLCC TYPE NAME AND FUNCTION
Vee 18 18 I Power Supply: This is the power supply voltage for normal, idle, and power-<:town operation.
PO.0-PO.7 17-1017-10 I/O pon 0: Port 0 is an 8-blt open-<:train, bidirectional I/O port. Port 0 is also the multiplexed data
and low-order address bus during accesses to external memory. External pullups are required
during program verification. Port 0 can sink/source eight LS TIL inputs.
P1.0-P1.7 23-3027-34 I/O pon 1: Port 1 is an 8-bit bidirectional I/O port with internal pullups. Port 1 receives the low-
order address bytes during program memory verification. Port 1 can sink/source three LS TTL
inputs, and drive CMOS inputs without external pullups.
P2.0-P2.7 2-9 2-9 I/O pon 2: Port 2 is an 8-bit bidirectional I/O port with internal pullups. Port 2 emits the hlgh-order
address bytes during access to external memory and receives the high-order address bits and
control signals during program verification. Port 2 can sink/source three LS TTL inputs and
drive CMOS inputs without external pullups.
P3.0-P3.7 32-39 36-43 I/O pon 3: Port 3 is an 8-bit bidirectional I/O port with internal pullups. Port 2 can sink/source
three LS TTL inputs and drive CMOS inputs without external pullups. Port 3 also serves the
special functions listed below:
32 36 I RxO (P3.0): Serial input port
33 37 0 TxO (P3.1): Serial output port
34 38 I INTO (P3.2): External interrupt 0
35 39 I INT1 (P3.3): External interrupt 1
37 41 I !!.{P3.5): Timer 1 external input
39 43 0 RO (P3.7): External data memory read strobe
P4.0-P4.3 22-19 I/O pon 4: Port 4 is a 4/8-bit (DIP/LCC) bidirectional I/O port with internal pullups. Port 4 can
P4.0-P4.7 26-19 I/O sink/source three LS TIL inputs and drive CMOS inputs without external pullups.
P5.0-P5.7 40-47 44-51 flO pon 5: Port 5 is an 8-bit bidirectional I/O port with internal pullups. Port 5 can sink/source
three LS TIL inputs and drive CMOS inputs without external pullups.
P6.0-P6.7 55-62 59-66 I/O pon 6: Port 6 is a specialized S-bit bidirectional I/O port with internal pullups. This special
port can sink/source three LS TTL inputs and drive CMOS inputs without external pull ups.
Port 6 can be used in a strobed or non-strobed mode of operation. Port 6 works in conjunc-
tion with four control pins that serve the functions listed below:
pon 6 Control Lines:
ODS 51 55 I ODS: Output data strobe
IDS 52 56 I IDS: Input data strobe
BFLAG 53 57 I/O BFLAG: Bidirectional I/O pin with internal pullups
AFLAG 54 58 I/O AFLAG: Bidirectional I/O pin with internal pullups
RST 31 35 I Reset: A high on this pin, for two machine cycles while the oscillator is running, resets the
device. An internal pull-<:town resistor permits a power-on reset using only a capacitor connect-
ed to Vee.
ALE 64 68 0 Address Latch Enable: Output pulse for latching the low byte of the address during accesses
to external memory. ALE is activated at a constant rate of 1/6 the oscillator frequency except
during an external data memory access, at which time one ALE is skipped. ALE can
sink/source eight LS TTL inputs and drive CMOS Inputs without an external pullup.
PSEN 63 67 0 Program Store Enable: The read strobe to external program memory. PSEN is activated twice
each machine cycle during fetches from external program memory. However, when executing
out of external program...!!!Jilllory, two activations of PSEN are skipped during each access to
~al data memory. PSEN is not activated during fetches from internal program memory.
PSEN can sink/source eight LS TTL inputs and drive CMOS inputs without an external pullup.
EA 1 1 I Instruction Execution Control: When EA is held high, the CPU executes out of internal program
memory, unless the program cou~r exceeds OFFFH. When EA is held low, the CPU executes
out of external program memory. EA must never be allowed to float.
XTAL1 49 53 I Crystal 1: Input to the inverting amplifier that forms the oscillator. This input receives the ex-
ternal oscillator when an external oscillator is used.
XTAL2 48 52 o Crystal 2: An output of the inverting amplifier that forms the oscillator. This pin should be
floated when an external oscillator is used.
February 1989 2-24

PORTS 4 AND 5 ODS - Output data strobe input for port control, or to output the state of the
Ports 4 and 5 are bidirectional 1/0 ports 6. ODS can be programmed to control output buffer full flag. AFLAG can also
with internal pullups. Port 4 is an 8-bit the port 6 output drivers and the output be programmed to be an input which se-
port (LCC version) or a 4-bit port (01 P buffer full flag (OBF), or to clear only lects whether the contents of the output
version). Port 4 and port 5 pins with the OBF flag bit in the CSR (output- buffer, or the contents of the port 6 con-
ones written to them, are pulled high by always mode). ODS is active low for trol status register will be output on port
the internal pullups, and in that state can output driver control. The OBF flag can 6. This feature grants complete port 6
be used as inputs. Port 4 and 5 are ad- be programmed to be cleared on the status to external devices.
dressed at the special function register negative or positive edge of ODS.
addresses shown in Table 1. BFLAG - BFLAG is a bidirectional 1/0
IDS- Input data strobe for port 6. IDS is pin which can be programmed to be an
PORT 6 used to control the port 6 input latch and output, set high or low under program
Port 6 is a special 8-bit bidirectional 1/0 input buffer full flag (IBF) bit in the CSR. control, or to output the state of the in-
port with internal pullups (see Figure 1). The input data latch can be programmed put buffer full flag. BFLAG can also be
This port can be used as a standard 1/0 to be transparent when IDS is low and programmed to input an enable signal for
port, or in strobed modes of operation in latched on the positive transition of IDS, port 6. When BFLAG is used as an en-
conjunction with four special control or to latch only on the positive transition able input, port 6 output drivers are in
lines: ODS, IDS, AFLAG, and BFLAG. of IDS. Correspondingly, the IBF flag is the high-impedance state, and the input
Port 6 operating modes are controlled by set on the negative or positive transition latch does not respond to the IDS strobe
the port 6 control status register (CSR). of IDS. when BFLAG is high. Both features are
Port 6 and the CSR are addressed at the enabled when BFLAG is low. This fea-
special function register addresses AFLAG - AFLAG is a bidirectional 1/0 ture facilitates the use of the SC80C451 1
shown in Table 1. The following four pin which can be programmed to be an SC83C451 in bused multiprocessor
control pins are used in conjunction with output set high or low under program systems.
port 6:

Port 4 P4 CO C7 C6 C5 C4 C3 C2 C1 CO
Port 5 P5 C8 CF CE CD CC CB CA C9 C8
Port 6 data P6 08 OF DE DO DC DB DA 09 08
AFLAG
Figure 1. Port 6 Block Diagram
February 1989 2-25

Signetlcs Microprocessor Products Product Specification

CONTROL STATUS REGISTER input buffer is loaded on the IDS positive source of port 6 output data. A logic 0
The control status register (CSR) estab- edge. When CSR.2 - 1, a high-to-low on AFLAG input selects the port 6 data
lishes the mode of operation for port 6 transition on the ~ pin sets the I BF register, and a logic 1 on AFLAG input
and indicates the current status of port 6 flag. When port 6 Input buffer is trans- selects the control status register.
i/O registers. All control status register parent when jjjS" is low, and latched
bits can be read and written by the CPU, when jjjS" is high. CSR.6, CSR.7 BFLAG Moda Salact (MBO,
except bits 0 and 1, which are read on- MB1) - Bits 6 and 7 select the mode
Iy. Reset writes ones to bits 2 through 7, CSR.3 Output Buffer Full Flag Clear operation as follows:
and writes zeros to bits 0 and 1 (see Ta- Mode (OBFC) - When CSR.3 - 1, the
positive edge of the ODS input clears MB1 MBO AFLAG Function
ble 2).
the OBF flag. When CSR.3 - 0, the o 0 Logic 0 output
CSR.O Input Buffar Full Flag (IBF) (Raad negative edge of the ODS input clears o 1 Logic 1 output
Only) - The I BF bit is set to a logic 1 the OBF flag. 1 0 IBF flag output (CSR.O)
when port 6 data is loaded into the input 1 1 Port enable (PE)
buffer under control of IDS. This can oc- CSR.4, CSR.5 AFLAG Mode Sal act (MAO,
cur on the negative or positive edge of MA1) - Bits 4 and 5 select the mode of In the port enable mode, IDS and ODS
IDS, as determined by CSR.2. IBF is operation for the AFLAG pin, as follows: inputs are disabled when BFLAG input is
cleared when the CPU reads the input high. When the BFLAG input is low, the
MA1 MAO AFLAG Function port is enabled for i/O.
buffer register.
o 0 Logic 0 output
CSR.1 Output Buffar Full Flag (OBF) o 1 Logic 1 output SPECIAL FUNCTION REGISTER
(Read Only) - The OBF flag is set to a 1 0 OBF flag output (CSR.1) ADDRESSES
1 1 Select (SEL) Input mode Special function register addresses for
logic 1 when the CPU writes to the port
the SC80C451/SC83C451 are identical
6 output data buffer. OBF is cleared by
The select (SEL) input mode is used to to those of the SC80C51, except for the
the positive or negative edge of ODS, as
determined by CSR.3. determine whether the port 6 data regis- additional registers listed in Table 1.
ter or the control status register is output
CSR.2 IDS Mode Salect (IDSM) - When on port 6. When the select feature is
CSR.2 - 0, a low-to-high tranSition on enabled, the AFLAG input controls the
the ~ pin sets the IBF flag. The port 6
Tabla 2. Control Status Ragister (CSR)
I
-rI
Bit 7 Bit 6 Bit 0 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
MB1 I MBO MA1 MAO OBFC IDSM OBF IBF
Output Buffer
Strobe Mode Full Flag Full Flag
Mode
0/0
0/1
- Logic 0 output
- Logic 1 output
0 -N~veO -
edge of ODS
Positive
edge of IDS
0- Output
data buffer
0- Input
data buffer
110 - IBF output 110 - OBF output" empty empty
111 - PE Input 111 - SEL Input 1 - Positive 1 - Low level
(0 - Select) (0 - Data) edge of ODS of IDS 1 - Output 1 - Input
(1 - Disable 1/0) (1 - Control/status) data buffer full data buffer full
NOTE.
"Output-always mode: MB1 - 0, MA1 - 1, and MAO - O. In this mode, port 6 is always enabled for output. ODS only clears
the OBF flag.
February 1989 2-26


I
PARAMETER RATING UNIT 1-
Operating temperature under bias

o to +70 °C
-40 to +85
1.5 W
NOleS:
noted.
DC ELECTRICAL CHARACTERISTICS TA - O°C to +70°C or TA - -40°C to +85°C, Vcc - 5V ±20%, VSS - OV
Limits
Min Typical 1 Max
VIL Input low voltage, except EA -0.5 0.2Vcc-0.1 V

VIL1 Input low voltage to EA 0 0. 2Vcc-0.3 V
VIH Input high voltage, except XT AL1, RST 0. 2Vcc+· 9 Vcc+0.5 V
VIH1 Input high voltage, XTAL1, RST 0. 7Vcc Vcc+0.5 V
VOH Output high voltage, ports 1, 2, 3 IOH - -601JA 2.4 V
IOH - -251JA 0. 75Vcc V
0. 9Vcc V
IOH - -1 01JA
VOH1 Output high voltage (port 0 in external bus IOH - -8001JA 2.4 V
mode, ALE, PSEN)3 IOH - -3001JA 0. 75Vcc V
IOH - -801JA 0. 9Vcc V
IlL Logical 0 Input current, ports 1, 2, 3 VIN - 0.45V -50 IJA

ITL LogicaI1-to-0 transition current, ports 1, 2, 3 See note 4 -650 IJA
III Input leakage current, port 0 VIN - VIL or VIH ±10 IJA
Active mode @ 12MHz5 11.5 25 rnA
Idle mode @ 12MHz5 1.3 4 rnA
Power down mode 3 50 IJA
RRST Internal reset pulldown resistor 50 300 k.Q
CIO Pin capacltance7 - DIP package 15 pF
- PLCC package 10 pF
NOleS:
at room temperature, 5V. '
to external bus capacitance discharging into the port 0 and port 2 pins when these pins make 1·to-0 transitions during bus operations. In
the worst cases (capacitive loading> 100pF), the noise pulse on the ALE pin may exceed O.SV. In such cases, it may be desirable to qualify
ALE with a Schmitt Trigger, or use an address latch with a Schmitt Trigger STROBE input.
3. Capacitive loading on ports 0 and 2 may cause the VOH on ALE and PSEN to momentarily fall below the 0.9VCC specification when the
5. leeMAX at other frequencies is given by:
Active mode: ICCMAX - 0,94 X FREQ + 13.71
Idle mode: ICCMAX - 0.14 X FREQ + 2.31
where FREQ is the external oscillator frequency in MHz. ICCMAX is given in rnA. See Figure 13.
7. CIO applies to Ports 1,2,3,4,5,6, AFLAG, BFLAG, XTAL1, XTAL2.
February 1989 2-27

AC ELECTRICAL CHARACTERISTICS TA - O°C to +70°C or TA - -40°C to +85°C, VCC - 5V ±20%, Vss - OV1, 2

Min Max Min Max
Program Memory
l/tCLCL 2 Oscillator frequency: Speed Versions
SC80C451/SC83C451 B 0.5 12 MHz
SC80C451/SC83C451 C 3.5 12 MHz
SC80C451/SC83C451 G 3.5 16 MHz
tLHLL 2 ALE pulse width 127 2tCLCL -40 ns
tAVLL 2 Address valid to ALE low 28 tCLCL -55 ns
tLLAX 2 Address hold after ALE low 48 tCLCL -35 ns
tpLPH 2 PSEN pulse width 205 3tCLCL -45 ns
tpLiV 2 PSEN low to valid instruction in 145 3tCLCL-l05 ns
tpXIZ 2 Input instruction float after PSEN 59 tCLCL-25 ns
tAVIV 2 Address to valid instruction in 312 5tcLCL -105 ns

Data Memory
tRLRH 3,4 RD pulse width 400 6tCLCL -100 ns
tWLWH 3, 4 WR pulse width 400 6tCLCL -100 ns
tRLDV 3,4 RD low to valid data in 252 5tCLCL -165 ns
tRHDX 3, 4 Data hold after R 0 0 0 ns
tRHDZ 3, 4 Data float after RD 97 2tCLCL -70 ns
tLLDV 3, 4 ALE low to valid data in 517 8tCLCL -150 ns
tAvDV 3, 4 Address to valid data in 585 9tCLCL -165 ns
tLLWL 3,4 ALE low to RD or WR low 200 300 3tCLCL -50 3tCLCL+50 ns
tAVWL 3, 4 Address valid to WR low or RD low 203 4tCLCL -130 ns
tOVWX 3, 4 Data valid to WR transition 23 tCLCL-60 ns

tRLAZ 3, 4 RD low to address float 0 0 ns

Shift Register
tXLXL 5 Serial port clock cycle time 1.0 12tCLCL J.1S
tOVXH 5 Output data setup to clock rising edge 700 1OtCLCL -133 ns
tXHOX 5 Output data hold after clock rising edge 50 2tCLCL -117 ns
tXHDV 5 Clock rising edge to input data valid 700 1OtCLCL -133 ns
NOTES.
February 1989 2-28

AC ELECTRICAL CHARACTERISTICS (Continued)

Min Max Min Max
Port 6 Input (input rise and fall times =5ns)
tFLFH 8 PE width 270 3tCLCL +20 ns
tlLlH 8 IDS width 270 3tCLCL +20 ns
tDVIH 8 Data setup to IDS high or PE high 0 0 ns
tlHDX 8 Data hold after IDS high or PE high 30 30 ns
tlVFV 9 IDS to BFLAG (IBF) delay 130 130 ns

Port 6 Output
tOLOH 6 ODS width 270 3tCLCL+20 ns
tFVDV 7 SEL to data out delay 85 85 ns
tOLDV 6 ODS to data out delay 80 80 ns
tOHDZ 6 ODS to data float delay 35 35 ns
tOVFV 6 ODS to AFLAG (OBF) delay 100 100 ns
tFLDV 6 PE to data out delay 120 120 ns

tOHFH 7 ODS high to AFLAG (SEL) delay 100 100 ns
External Clock

EXPLANATION OF THE AC SYMBOLS

Each timing symbol has five characters. The first character is
always 't' (- time). The other characters, depending on their
positions, indicate the name of a signal or the logical status of
that signal. The designations are:
A - Address
C - Clock
0- Input data
F - PE, SEL, or IBF
H - Logic level high
I - Instruction (program memory contents), or input data strobe
o- Output data strobe
P- PSEN
Q - Output data
R - RD signal
t - Time
V - Valid
W - WR signal
X - No longer a valid logic level
Z - Float
Examples: tAVLL - Time for address valid to ALE low.

tLLPL - Time for ALE low to PSEN 10w.L - Logic I
February 1989 2-29

ALE
PORTO _ _ _ _/
PORT 2 _ _ _ _J A8-A15
ALE
10----- 'lLDV ----001

-~~----'RlRH------~
'RHDX
PORTO AO-A? FROM PCl
Io----------'AVDV~----~
PORT 2
--- P2.0-P2.? OR AS-A15 FROM DPH A8-A15 FROM PCH
February 1989 2-30

ALE
- ....---WLWH----01
tOVWX
PORTO DATA OUT
PORT 2 P2.0-P2.7 OR A8-A15 FROM DPH A8-A15 FROM PCH

---'
ALE
tOVXH HI t XHOX
OUTPUT DATA
' ' - _ - J "--_-' ' - _ - J ' - - _ . . J ' - _ - J ' - - _ - ' ' - _ - J '--_....J
f
WRITE TO SBUF
I INPUT DATA I _ _ _ _ _ _ _ _ _ _ _ _,~--'~---I'~~··?
f
CLEAR RI
SET RI
February 1989 2-31

~ -' I.-
OBF (AFLAG) k::
1----0 tOVFV ~ tOVFV
~ ...., t<-
PE(BFlAG) ~
t OLOH
~ Ir- -: £.
tOLDV I-- tOHDZ
PORT 6
10-- tFLDV -
Figure 6. Port 6 Output
...., ~
I------ tOHFH
:; I'- ~
~ I'-
"to--
SEL (AFLAG)
I----- t FvDV t FVDV
PORT 6 DATA CSR DATA
Figure 7. Port 6 Select Mode
I
tFLFH
PE (BFLAG) ~ ~~
I
tlllH
"{ 7 I'-
t Dv1H
tlHDX
PORTS
Figure 8. Port 6 Input
'" "'~:) ~~~~~~~~~~~~~~~-t!--.Lj.-:I-VF-v---------i+_IV_FV _ _ _ __
Figure 9. ISF Flag Output
February 1989 2-32

0.45V
~----------tCLCL----------~
Vcc-o.s
°.45V
=x O.2Vcc+O.9 >C
_,-O.;.;..;;.2V.;,.C;,.;c.;..-,.;;.O;,.;., _ _.....
Timing
Reference
Points
<
AC inputs during testing are driven at Vcc-o.s
for a logic "1" and O.4SV for a logic "0".
the loaded VOHIVOL level occurs.IOH/lOL~± 20mA.

30
MAX
ACTIVE MODE
25
20
f
<.
E 15
()
!:!
10
5 ~---+~~+----4----~MAX
IDLE MODE
TYP(1)
L:::d=:::::±==:t:==:J IDLE MODE
FREQ AT XTAL1

TYP(1) - See DC Electrical Characteristics
February 1989 2-33

Vee
Vee
RST
RST
(NC) XTAL2
(NC) XTAL2 CLOCK XTAL1 Vee
CLOCK XTAL1 SIGNAL Vss
SIGNAL Vss
Figure 14. Icc Test Condition, Active Mode Figure 15. Icc Test Condition, Idle Mode
All other pins are disconnected All other pins are disconnected
0.45V
~--------tCLCL----------~
tCLCH = tCHCL 5ns=
RST
(NC) XTAL2
XTAL1 Vee
Vss

February 1989 2-34

Signetics SC87C451
CMOS Single-Chip 8-Bit EPROM
Microcontroller

The Signetics SC87C451 is an I/O ex- • User programmable microcontroller
panded, single-chip microcontroller fabri-
cated with Signetics high-density CMOS
• SC80C51 based architecture
• 681'in LCC and 641'in DIP EA/vPP II ~ ~ROG
technology. Signetics epitaxial substrate packages: P2.0/A8 ~ ~ PSEN
- Seven 8-bit I/O ports (LCC P2.1/A9 3 S2 PS.7
minimizes latch-up sensitivity. version)
- Six 6-bit ports and one 4-bit P2.2/Al0 ~ ~ P6.S
The SC87C451 has 4K of EPROM on- port (DIP version) P2.3/All ,l ~ PS.5
chip as program memory and is other- • Port 6 features: P2.4/A12 ~ ~ P6.4
wise identical to the SC83C451. - 8 data pins P2.5/A13 ~ ~ PS.3
- 4 control pins
The SC87C451 is a functional extension - Direct MPU bus interface P2.6/A14.! ~ PS.2
of the SC87C51 microcontroller with - Parallel printer interface P2.7/A15 .! ~ PS.l
three additional I/O ports and four I/O • On the microcontroller PO.7/AD7 il2 55 P6.0
control lines. The LCC version has a total
of 68 pins. Four control lines associated
- 4KX 8 EPROM
- 128X 8 RAM PO.S/ADS~ ~ AFLAG
with port 6 facilitate high speed asyn- - Two 16-bit counter/timers PO.5/AD5~ ~ ~AG
chronous I/O functions. - Two external interrupts PO.4/AD4~ ~ ~
• External memory addressing PO.3/AD3~ ~ ODS
The SC87C451 includes a 4K X 8 capability
PO.2/AD2~ 50 Vss
- 64K ROM and 64K RAM
EPROM, a 128 X 8 RAM, 58 (LCC) or 54
(DIP) I/O lines, two 16-blt timer/count-
• Low power consumption: PO.l/ADl ~ ~ XTALl
- Normal operation: less than PO.O/ADO~ DIP ~ XTAL2
ers, a five source, two priority level, 24mA at 5V, 12MHz
nested interrupt structure, a serial I/O VCC~ ~ P5.7
- Idle mode
port for either a full duplex UART, I/O - Power-down mode P4.3~ ~ ps.s
expansion, or multiprocessor communica- P4.2~ ~ P5.5
tions, and an on-chip oscillator and clock LOGIC SYMBOL P4.1 ~ ~ P5.4
circuits. P4.0~ ~ P5.3
The SC87C451 has two software select- Pl.0~ ~ P5.2
able modes of reduced activity for fur- Pl.l ~ ~ P5.1
ther power reduction: Idle mode and Pl.2~ ~ P5.0_
power-down mode. Idle mode freezes Pl.3~ ~ P3.7/~
the CPU while allowing the RAM, timers, Pl.4~ ~ P3.S/WR
serial port, and interrupt system to con-
Pl.5 ~ ~ P3.5/Tl
tinue functioning. Power-down mode
freezes the OSCillator, causing all other Pl.S ~ ~ P3.4/~
chip functions to be inoperative while Pl.7~ ~ P3.3~
maintaining the RAM contents. RST ~ ~ P3.2/INTO
P3.0/RxD ~,-_ _~1=_33_ P3.1 /TxD
TOP VIEW
INDEX
CORNE1~9
: 61 so
LCC
26 44
27 43
TOP VIEW
See next page for LCC pin functions
February 1989 2-35 ECN 94521

SC87C451 cC!:!:',!:! PART NUMBER SELECTION

Pan No. Speed Temperature and Package
SC87C451 CCI64 3.5 to 12MHz o to +70 "C ceramic 01 P
SC87C451CGI64 3.5 to 16MHz o to +70·Cceramic DIp·
SC87C451CBI64 0.5 to 12MHz o to +70"Cceramic DIP
SC87C451 CCl68 3.5 to 12MHz o to +70·Cceramic LCC
SC87C451 CGl68 3.5 to 16MHz o to +70"Cceramic LCC·
SC87C451CBL68 0.5 to 12MHz o to +70·Cceramic LCC
OPERATING
SC87C451 CCN64 3.5 to 12MHz o to +70"Cplastic DIP
TEMPERATURE RANGE -
A - -40°C to +85 0 C
~64
68
=
=64 pin DIP
68 pin lCC
SC87C451 CGN64 3.5 to 16MHz o to +70 "C plastic 01 p.
C - oOC to +70OC SC87C451CBN64 0.5 to 12MHz o to +70"C plastic DiP
SC87C451 CCA68 3.5 to 12MHz o to +70"C plastic LCC
SPEED- '---PACKAGE SC87C451CGA68 3.5 to 16MHz o to +70"C plastic LCC·
B - 0.5 to 12MHz A - Plastic LCC SC87C451CBA68 0.5 to 12MHz o to +70"C plastic LCC
C - 3.5 to 12MHz I - Ceramic DIP
G - 3.5 to 16MHz L - Ceramic LCC 'PRELIMINARY SPECIFICATION
N - Plastic DIP
lCC PIN FUNCTIONS
INDEX
~"n
10 0 60
LCC
26 44
27 43
TOP VIEW
Pin Function Pin Function Pin Function
1 EAIVPP 24 P4.2 47 P5.3
2 P2.0/A8 25 P4.1 48 P5.4
3 P2.1/A9 26 P4.0 49 P5.5
4 P2.2/Al0 27 Pl.0 50 P5.6
5 P2.3/All 28 Pl.l 51 P5.7
6 P2.4/A12 29 Pl.2 52 XTAL2
7 P2.5/A13 30 Pl.3 53 XTALl
8 P2.6/A14 31 Pl.4 54 Vss
9 P2.7/A15 32 Pl.5 55 ODS
10 PO.7IAD7 33 Pl.6 56 ~
11 PO.6/AD6 34 Pl.7 57 BFLAG
12 PO.5/AD5 35 RST 58 AFLAG
13 PO.4/AD4 36 P3.0/RxD 59 P6.0
14 PO.3/AD3 37 P3.1/TxD 60 P6.1
15 PO.2/AD2 38 P3.2/iliiTli 61 P6.2
16 PO.l/ADl 39 P3.3/iN'i'i 62 P6.3
17 PO.O/ADO 40 P3.4/TO 63 P6.4
18 Vee 41 P3.5/Tl 64 P6.5
19 P4.7 42 P3.6/ioWi 65 P6.6
20 P4.6 43 P3.7/RD 66
21 P4.5 44 P5.0 67 ~~'~N
22 P4.4 45 P5.1 68 ALE/PROO
23 P4.3 46 P5.2
February 1989 2-36

.,.,
CD
cr OJ (f)
r
-<"
I» 0 0 <5.
0
s:: ::J
~
'"
00
"i>c 0 n·
(j)
CJ) s::
'" PO.D-PO.7 P2.CI-P2.7 P4.o-P4.7 P5.o-P5.7
G)
1I
CJ)
n·
(3
> -a
3:
( ---------1 ::::l
<C
(3
()
CD
F. 0
CD
I
::r
"0
III
Q
""0
(3
Q.
c
()
en
CXl
I
-
OJ
m
-0
JJ
0
s::
'" s::
I
'".... PCON ISCON ITMODI

THO TLO
TCON
THl
o·
~
TL1 0
SBUFI IE I IP 0
-
0
::::l
~
0
ffiN CD
AL~G
T~~~ ~m~ ~; ~ ~
~
EA/V"" J DPTR
RST ~
CONTROL - 1f ,q.,q.
if ; ;
1"f
l XTALl XTAL2
-----) ""0
lI! CJ) a
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CXl -a
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()
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01
....0. o·~
::J
PIN DESCRIPTION
PIN NO.
DIP LCC
Vee 18 18 I Power Supply: This is the power supply voltage for normal, idle, and power-down operation.
PO.0-PO.7 17-10 17-10 I/O Port 0: Port 0 is an 8-bit open-drain, bidirectional I/O port. Port 0 is also the multiplexed data
and low-<lrder address bus during accesses to external memory. External pullups are required
during program verification. Port 0 can sink/source eight LS TTL inputs.
Pl.0-Pl.7 23-3027-34 I/O Port 1: Port 1 is an 8-bit bidirectional I/O port with internal pull ups. Port 1 receives the low-
order address bytes during program memory verification. Port 1 can sink/source three LS TTL
inputs, and drive CMOS inputs without external pullups.
P2.0-P2.7 2-9 2-9 I/O Port 2: Port 2 is an 8-bit bidirectional I/O port with internal pullups. Port 2 emits the
high-order address bytes during access to external memory and receives the high-<lrder
address bits and control signals during program verification. Port 2 can sink/source three LS
TTL inputs and drive CMOS inputs without external pullups.
P3.0-P3.7 32-39 36-43 I/O Port 3: Port 3 is an 8-bit bidirectional I/O port with internal pullups. Port 2 can sink/source
three LS TTL inputs and drive CMOS inputs without external pullups. Port 3 also serves the
special functions listed below:
32 36 I RxO (P3.0): Serial input port
33 37 0 TxO (P3.1): Serial output port
34 38 I INTO (P3.2): External interrupt 0
35 39 I INT1 (P3.3): External interrupt 1
37 41 I lliP3.5): Timer 1 external input
39 43 0 RO (P3.7): External data memory read strobe
P4.0-P4.3 22-19 I/O Port 4: Port 4 is a 4/8-bit (DIP/LCG) bidirectional I/O port with internal pull ups. Port 4 can
P4.0-P4.7 26-19 I/O sink/source three LS TTL inputs and drive CMOS inputs without external pullups.
P5.0-P5.7 40-47 44-51 I/O Port 5: Port 5 is an 8-bit bidirectional I/O port with internal pullups. Port 5 can sink/source
three LS TTL inputs and drive CMOS inputs without external pullups.
P6.0-P6.7 55-62 59-66 I/O Port 6: Port 6 is a specialized 8-bit bidirectional I/O port with internal pull ups. This special
port can sink/source three LS TTL inputs and drive CMOS inputs without external pull ups.
Port 6 can be used in a strobed or non-strobed mode of operation. Port 6 works in conjunc-
tion with four control pins that serve the functions listed below:
Port 6 Control Lines:
51 55 ODS: Output data strobe
52 56 IDS: Input data strobe
53 57 BFLAG: Bidirectional I/O pin with internal pullups
54 58 AFLAG: Bidirectional I/O pin with internal pull ups
RST 31 35 I Reset: A high on this pin, for two machine cycles while the oscillator is running, resets the
device. An internal pull-down resistor permits a power-<ln reset using only a capacitor connect-
ed to Vee.
ALE/PROG 64 68 I/O Address Latch Enable/Program Pulse: Output pulse for latching the low byte of the address
during accesses to external memory. ALE is activated at a constant rate of 1/6 the oscillator
frequency except during an external data memory access, at which time one ALE is skipped.
ALE can sink/source eight LS TTL inputs and drive CMOS inputs without an external pullup.
This pin is also the program pulse during EPROM programming.
PSEN 63 67 I/O Program Store Enable: The read strobe to external program memory. PSEN is activated twice
each machine cycle during fetches from external program memory. However, when executing
out of external program.1!!!ill!.0ry, two activations of PSEN are skipped during each access to
~al data memory. PSEN is not activated during fetches from internal program memory.
PSEN can sink/source eight LS TIL inputs and drive CMOS inputs without an external pull up.
This pin should be tied low during programming.
EA/vpp 1 1 I Instruction Execution Control/Programming Supply Voltage: When EA is held high, the CPU
~ecutes out of internal program memory, unless the program count.N..exceeds OFFFH. When
EA is held low, the CPU executes out of external program memory. EA must never be allowed
to float. This pin also receives the 12.75V programming supply voltage (Vpp) during EPROM
programming.
XTAL1 49 53 I Crystal 1: Input to the inverting amplifier that forms the oscillator. This input receives the ex-
ternal oscillator when an external oscillator is used.
XTAL2 48 52 0 Crystal 2: An output of the inverting amplifier that forms the oscillator. This pin should be
floated when an external oscillator is used.
February 1989 2-38

PORTS 4AND5 ODS - 0 utput data strobe input for port control, or to output the state of the
Ports 4 and 5 are bidirectional 1/0 ports 6. O~S can be programmed to control output buffer full flag. AFLAG can also
with internal pullups. Port 4 is an 8.oit the port 6 output drivers and the output be programmed to be an input which se-
port (LCC version) or a 4.oit port (01 P buffer full flag (OBF), or to clear only lects whether the contents of the output
version). Port 4 and port 5 pins with the OBF flag bit in the CSR (output- buffer, or the contents of the port 6 con-
ones written to them, are pulled high by always mode). ODS is active low for trol status register will be output on port
the internal pullups, and in that state can output driver control. The OBF flag can 6. This feature grants complete port 6
be used as inputs. Port 4 and S are ad- be programmed to be cleared on the status to external devices.
dressed at the special function register negative edge of ODS.
addresses shown in Table 1. BFLAG - BFLAG is a bidirectional I/O
IDS- Input data strobe for port 6. IDS is pin which can be programmed to be an
PORTe used to control the port 6 input latch and output, set high or low under program
Port 6 is a special 8.oit bidirectional 1/0 input buffer full flag (IBF) bit in the CSR. control, or to output the state of the in-
port with internal pullups (see Figure 1). The input data latch can be programmed put buffer full flag. BFLAG can also be
This port can be used as a standard 1/0 to be transparent when IDS is low and programmed to input an enable signal for
port, or in strobed modes of operation in latched on the positive transition of i"DS, port 6. When BFLAG is used as an en-
conjunction with four special control or to latch only on the positive transition able input, port 6 output drivers are in
lines: ODS, IDS, AFLAG, and BFLAG. of IDS. Correspondingly, the IBF flag is the high-impedance state, and the input
Port 6 operating modes are controlled by set on the negative or positive transition latch does not respond to the IDS strobe
the port 6 control status register (CSR). of IDS. when BFLAG is high. Both features are
Port 6 and the CSR are addressed at the enabled when BFLAG is low. This fea-
special function register addresses AFLAG - AFLAG is a bidirectional I/O ture facilitates the use of the SC87C4S1
shown in Table 1. The following four pin which can be programmed to be an in bused multiprocessor systems.
control pins are used in conjunction with output set high or low under program
port 6:

Port 4 P4 CO C7 C6 CS C4 C3 C2 C1 CO
Port S PS C8 CF CE CD CC CB CA C9 C8
Port 6 data P6 08 OF DE DO DC DB OA 09 08
AFLAG
Figure 1. Port 6 Block Diagram
February 1989 2-39

CONTROL STATUS REGISTER Input buffer is loaded on the IDS positive source of port 6 output data. A 'logic 0
The control status register (CSR) estab- edge. When CSR.2 - 1, a high-to-low on AFLAG input selects the port 6 data
lishes the mode of operation for port 6 transition on the ii5S pin sets the I BF register, and a logic 1 on AFLAG input
and indicates the current status of port 6 flag. When port 6 input buffer is trans- selects the control status register.
I/O registers. All control status register parent when IDS is low, and latched
bits can be read and written by the CPU, when ii5S is high. CSR.6, CSR.7 BFLAG Mode Select (MBO,
except bits 0 and 1, which are read on- MB1) - Bits 6 and 7 select the mode
ly. Reset writes ones to bits 2 through 7, CSR.3 Output Buffer Full Flag Clear operation as follows:
and writes zeros to bits 0 and 1 (see Ta- Mode (OBFe) - When CSR.3 - 1, the
positive edge of the ~ input clears MA1 MAO AFLAG Function
ble 2). o 0 Logic 0 output
the OBF flag. When CSR.3 - 0, the
CSR.O Input Buffer Full Flag (IBF) (Read negative edge of the ODS input clears o 1 Logic 1 output
Only) ~ The IBF bit Is set to a logic 1 the OBF flag. 1 0 IBF flag output (CSR.O)
when port 6 data Is loaded into the input 1 1 Port enable (PE)
buffer under control of ii5S. This can oc- CSR.4, CSR.5 AFLAG Mode Select (MAO,
cur on the negative or positive edge of MA1) - Bits 4 and 5 select the mode of In the port enable mode, IDS and ODS
IDS, as determined by CSR.2. IBF is operation for the AFLAG pin, as follows: inputs are disabled when BFLAG input is
cleared when the CPU reads the input high. When the BFLAG input Is low, the
MA1 MAO AFLAG Function port is enabled for I/O.
buffer register.
o 0 Logic 0 output
CSR.1 Output Buffer Full Flag (OBF) o 1 Logic 1 output SPECIAL FUNCTION REGISTER
(Read Only) - The OBF flag is set to a 1 0 OBF flag output (CSR.1) ADDRESSES
1 1 Select (SEL) input mode Special function register addresses for
logic 1 when the CPU writes to the port
the SC87C451 are identical to those of
6 output data buffer. OBF is cleared by
The select (SEL) input mode is used to the SC80C51, except for the additional
the positive or negative edge of ODS, as
determine whether the port 6 data regis- registers listed in Table 1.
determined by CSR.3.
ter or the control status register is output
CSR.2 IDS Mode Select (IDSM) - When on port 6. When the select feature is
CSR.2 - 0, a low-to-high transition on enabled, the AFLAG input controls the
the IDS pin sets the IBF flag. The port 6
Table 2. Control Status Register (CSR)
Bit 7 I Bit 6 Bit 5 I Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

MB1 I MBO MA1 I MAO OBFC IDSM OBF IBF
Output Buffer
Strobe Mode Full Flag Full Flag
Mode
0/0
011
- Logic 0 output
- Logic 1 output
0 -N~ve o -
edge of ODS
Positive
edge of IDS
0- Output
data buffer
0- Input
data buffer
1/0 - IBF output 1/0 - OBF output" empty empty
1/1 - PE input 1/1 - SEL input 1 - Positive 1 - Low level
(0 - Select) (0 - Data) edge of ODS of IDS 1 - Output 1 - Input
(1 - Disable I/O) (1 - Control/status) data buffer full data buffer full
NOTE.
"Output-always mode: MB1 - 0, MA1 - 1, and MAO - O. In this mode, port 6 is always enabled for output. ODS only clears
the OBF flag.
February 1989 2-40


Operating temperature under bias

o to +70
°C
-40 to +85
Voltage on EA/vpp pin to VSS o to +13.0 V
1.5 W
NOTES:
2. This product inctudes circuitry specifically designed for the protection of its internal devices from the damaging effects of excessive static
charge. Nonetheless. it is suggested that conventional precautions be taken to avoid applying voltages greater than the rated maxima.
noted.
DC ELECTRICAL CHARACTERISTICS TA - O°C to +70°C or TA - -40°C to +85°C, Vcc - 5V ±10%, Vss - OV
Test Limits
Symbol Parameter Unit
Conditions Min Typical 1 Max
VIL Input low voltage, except EA -0.5 0. 2Vcc-0.1 V
VIL1 Input low voltage to EA 0 0.2Vcc-0.3 V
VIH Input high voltage, except XT AU, RST 0.2Vcc+·9 Vcc+0.5 V
VIH1 Input high voltage, XTAL 1, RST 0.7Vcc Vcc+O.5 V
VOL Output low voltage, ports 1, 2, 3, 4, 5, 6 IOL - 1.6mA2 0.45 V
VOH Output high voltage, ports 1, 2, 3, 4, 5, 6 IOH - -60jJA 2.4 V
IOH - -25jJA O.75VcC V
IOH - -10jJA 0.9Vcc V
VOH1 Output high voltage (port 0 in external bus IOH - -800jJA 2.4 V
mode, ALE, PSEN)3 IOH - -300jJA 0.75Vcc V
IOH - -80jJA 0. 9Vcc V
IlL Logical 0 input current, ports 1, 2, 3, 4, 5, 6 VIN - 0.45V -50 jJA

ITL Logical 1-to-0 transition current, ports 1, 2, 3, 4, 5, 6 See note 4 -650 jJA
III Input leakage current, port 0 VIN - VIL or ±10 jJA
VIH
Active mode @ 12MHz5 11.5 25 rnA
Idle mode @ 12MHz5 1.3 4 rnA
Power down mode 3 50 jJA
RRST Internal reset pulldown resistor 50 300 kQ
CIO Pin capacitance7 - DIP package 15 pF
- PLCC package 10 pF
NOTES:
2. Capacitive loading on ports a and 2 may cause spurious noise to be superimposed on the VOLs of ALE and ports 1 and 3. The noise is due
to external bus capacitance discharging into the port 0 and port 2 pins when these pins make 1-to-O transitions during bus operations. In
the worst cases (capacitive loading> 100pF), the noise pulse on the ALE pin may exceed O.SV. In such cases, it may be desirable to qualify
ALE with a Schmitt Trigger, or use an address latch with a Schmit! Trigger STROBE input.
3. Capacitive loading on ports 0 and 2 may cause the YOH on ALE and PSEN to momentarily fall below the 0.9YCC specification when the
4. Pins of ports 1, 2, and 3 source a transition current when they are being externally driven from 1 to-'O. The transition current reaches its
5. ICCMAX at other frequencies is given by:
Active mode: ICC MAX - 0.94 X FREQ + 13.71
Idle mode: ICCMAX - 0.14 X FREQ + 2.31
where FREQ is the external oscillator frequency in MHz. ICCMAX is given in rnA. See Figure 13.
7. CIO applies to Ports 1, 2, 3, 4, 5, 6, AFLAG, BFLAG, XTAL1, XTAL2.
February 1989 2-41

AC ELECTRICAL CHARACTERISTICS TA - DoC to +70°C or TA - -40°C to +85°C, VCC - 5V ±10%, Vss - OV1, 2

Min Max Min Max
Program Memory
l/tCLCL 2 Oscillator frequency: Speed Versions
SC87C451 8 0.5 12 MHz
SC87C451 C 3.5 12 MHz
SC87C451 G 3.5 16 MHz
tLHLL 2 ALE pulse width 127 2tCLCL-40 ns
tLLAX 2 Address hold after ALE low 48 tCLcL -35 ns
tLLPL 2 ALE low to PSEN low 43 tCLCL-40 ns
tpLiV 2 PSEN low to valid instruction in 145 3tCLCL -105 ns

Data Memory
tRLRH 3, 4 RD pulse width 400 6tCLCL -100 ns
tWLWH 3, 4 WR pulse width 400 6tCLCL-100 ns
tRLDV 3, 4 RD low to valid data in 252 5tCLCL-165 ns
tRHDZ 3, 4 Data float after RD 97 2tCLCL-70 ns
tLLDV 3, 4 ALE low to valid data in 517 8tCLCL-150 ns
tAvDV 3, 4 Address to valid data in 585 9tCLCL-165 ns
tLLWL 3, 4 ALE low to RD or WR low 200 300 3tCLCL-50 3tCLCL+50 ns
tAVWL 3,4 Address valid to WR low or RD low 203 4tCLCL-130 ns
tOVWX 3,4 Data valid to WR transition 23 tCLCL-60 ns
tWHOX 3, 4 Data hold after WR 33 tCLCL -50 ns
tWHLH 3,4 RD or WR high to ALE high 43 123 tCLCL-40 tCLCL+40 ns

Shift Register
tXLXL 5 Serial port clock cycle time 1.0 12tCLCL !IS
tOVXH 5 Output data setup to clock rising edge 700 1OtCLCL -133 ns

NOTES:
2. Load capacitance for port 0, ALE, and PSEN - 100pF. load capacitance for all other outputs - 80pF.
February 1989 2-42


Min Max Min Max
Port 6 Input (input rise and fall times = 5ns)
tFLFH 8 PE width 270 3tCLCL+20 ns
tlLlH 8 IDS width 270 3tCLCL +20 ns
tDVIH 8 Data setup to IDS high or PE high 0 0 ns
tlHDX 8 Data hold after IDS high or PE high 30 30 ns
tlVFV 9 IDS to BFLAG (lBF) delay 130 130 ns
Port 6 Output
tOLOH 6 ODS width 270 3tCLCL +20 ns
tFVDV 7 SEL to data out delay 85 85 ns
tOLDV 6 ODS to data out delay 80 80 ns
tOHDZ 6 ODS to data float delay 35 35 ns
tOVFV 6 ODS to AFLAG (OBF) delay 100 100 ns
tFLDV 6 PE to data out delay 120 120 ns
tOHFH 7 ODS high to AFLAG (SEL) delay 100 100 ns

External Clock

Each timing symbol has five characters. The first character is
always 't' (- time). The other characters, depending on their
positions, indicate the name of a signal or the logical status of
that signal. The designations are:
A - Address
C - Clock
o - I nput data
F - PE, SEL, or IBF
H - LogiC level high
I - I nstruction (program memory contents), or input data strobe
a- Output data strobe
P- PSEN
Q - Output data
R - RD signal
t - Time
V - Valid
W - WR signal
X - No longer a valid logic level
Z - Float
Examples: tAVLL - Time for address valid to ALE low.

tLLPL - Time for ALE low to PSEN 10w.L - Logic I
February 1989 2-43

ALE
~ _ _ _J
PORTO _ _ _J
PORT 2 _ _ _ _J
ALE
---M.------IRlRH------~
PORTO AO-A7 FROM PCl

1o----IAVWl
Io-------IAVDV------~
PORT 2 P2.0-P2.7 OR AS-A 15 FROM DPH AS-A15 FROM PCH

----'
February 1989 2-44

ALE "- /
I-- tWHLH
I--- t LLWL t WLWH
1\
t AVLL
- ..-tLLAX .....
- tOVWX
/
..... t wHoX
PORT 0
~ . ",,,,,.A~ I ~~ nDI ~ DATA OUT K AD-A7 FROM PCL INSTR I N
tAVWL
PORT 2 )< P2.0-P2.7 OR A8-A15 FROM DPH A8-A15 FROM PCH
INSTRUCTION o 2 3 4 5 6 7 B
ALE
tOVXH H I ' X H Q X
OUTPUT DATA
\ ...._ - - ' '--_...J \.._--' I - - _ . . J ...._ - - ' '--_..J ...._----1 \..o-_..J
T
WRITE TO SBUF
I INPUT DATA I __________- J
f
CLEAR RI t
SET RI
February 1989 2-45

~~ -'
OBF (AFLAG)
I----t tOVFV to--- "

tOVFV
..J
"7 IL
"
PE(BFLAG)
..::~
t OLOH
.., IL
tOLDV I--t tOHDZ
PORTe
I-- tFLDV ---
Figure 6. Port 6 Output
"7 l£-
I-- tOHFH
-~
SEL (AFLAG) "7 IL "7 l£-
I--- t FVDV ""

I----- t FVDV
PORTe DATA eSR DATA
Figure 7. Port 6 Select Mode
I
tFLFH
PE (BFLAG) ~ -:: IL
~
tlLlH
.., F-
t DV1H
tlHDX
PORTe
Figure 8. Port 6 Input
IBF (BFLAG)
IDS
-
~
_
;,~ iJ_ 1VFV
Figure 9. ISF Flag Output
February 1989 2-46

0.45V
~---------tCLCL--------~
Vcc-O.5
O.45V
=x O.2Vcc+O.9
_...O;;,;.,:;;2V.:.,c,;;.c,;;.-..,;O.:...,:......___
>C Timing
Reference
Points
<
a logic" 1" and V IL max for a logic "0".

EPROM CHARACTERISTICS applied to port O. RST, PSEN and pins shown in Figure 20. The other pins are
The SC87C451 is programmed by using a of ports 2 and 3 specified in Table 2 are held at the "Verify Code Data" levels in-
modified Quick-Pulse Programming" al- held at the "Program Code Data" levels dicated in Table 3. The contents of the
gorithm. It differs from older methods in indicated in Table 3. The ALE/PROG is address location will be emitted on port
the value used for Vpp (programming pulsed low 25 times as shown in Figure O. External pull-ups are required on port
supply voltage) and in the width and 19. o for this operation.
number of the ALE/PROG pulses.
To program the encryption table, repeat If the encryption table has been pro-
The SC87C451 contains two signature the 25 pulse programming sequence for grammed, the data presented at port 0
bytes that can be read and used by an addresses 0 through 1 FH, using the will be the exclusive NOR of the pro-
EPROM programming system to identify "Pgm Encryption Table" levels. Do not gram byte with one of the encryption
the device. The signature bytes identify forget that after the encryption table is bytes. The user will have to know the
the device as an SC87C451 manufac- programmed, verification cycles will pro- encryption table contents in order to cor-
tured by Signetics Corporation. duce only encrypted data. rectly decode the verification data. The
encryption table itself cannot be read
Table 3 shows the logic levels for read- To program the lock bits, repeat the 25 out.
ing the signature byte, and for program- pulse programming sequence using the
ming the program memory, the encryp- "Pgm Lock Bit" levels. After one lock bit Reading the Signature Bytes
tion table, and the lock bits. The circuit is programmed, further programming of The signature bytes are read by the
configuration and waveforms for quick- the code memory and encryption table is same procedure as a normal verification
pulse programming are shown in Figures disabled. However, the other lock bit of locations 030H and 031 H, except that
18 and 19. Figure 20 shows the circuit can still be programmed. P3.6 and P3.7 need to be pulled to a
configuration for normal program memory logic low. The values are:
verification. Note that the EAIVpp pin must not be al-
lowed to go above the maximum speci- (030H) - 15H indicates manufactured by
QUICK-PULSE PROGRAMMING fied Vpp level for any amount of time. Signetics
The setup for microcontroller quick-pulse Even a narrow glitch above that voltage (031 H) - 90H indicates SC87C451
programming is shown in Figure 18. Note can cause permanent damage to the de-
that the SC87C451 is running with a 4 to vice. The Vpp source should be well reg- ProgramlVerify Algorithms
6MHz oscillator. The reason the oscilla- ulated and free of glitches and over- Any algorithm in agreement with the
tor needs to be (unning is that the de- shoot. conditions listed in Table 3, and which
vice is executing internal address and satisfies the timing specifications, is suit-
program data transfers. Program Verification able.
If lock bit 2 has not been programmed,
The address of the EPROM location to the on-chip program memory can be
be programmed is applied to ports 1 and read out for program verification. The
2, as shown in Figure 18. The code byte address of the program memory locations
to be programmed into that location is to be read is applied to ports 1 and 2 as "Trademark phrase of Intel Corp.
February 1989 2-47

E rasure Characteristics The recommended erasure procedure is

Erasure of the EPROM begins to occur exposure to ultraviolet light (at 2537
when the chip is exposed to light with angstroms) to an integrated dose of at
wa velengths shorter than approximately least 15W-sec/cm2. Exposing the
4,000 angstroms. Since sunlight and flu- EPROM to an ultraviolet lamp of
orescent lighting have wavelengths in 12,OOOIlW/cm2 rating for 20 to 39 min-
this range, exposure to these light utes, at a distance of about 1 inch,
sources over an extended time (about 1 should be sufficient.
week in sunlight, or 3 years in room level
fluorescent lighting) could cause inadver- Erasure leaves the array in an all 1s
tent erasure. For this and secondary ef- state.
fects, it is recommended that an
opaque label be placed over the win-
dow. For elevated temperature or sol-
vent environment, use Kapton tape
Fluorglas part number 2345-5 or equiva-
lent.
Table 3, EPROM Programming Modes
MODE RST PSEN ALE/PROG EANpp P2.7 P2.B P3.7 P3.B

Program code data 1 0 O' Vpp 1 0 1 1
Pgm encryption table 1 0 O' Vpp 1 0 1 0
NOTES:
1. '0' - valid low for that pin, '1" - valid high for that pin.
2, Vpp = 12.75V ±O.25V.
3. Vee - 5V ±10% during programming and verification.
'ALE/i5"R1X3 receives 25 programming pulses while Vpp Is held at 12.75V. Each programming pulse is low for 100/lS (±10/lS) and
high for a minimum of 10/lS.
30
MAX
ACTIVE MODE
t
1 15
~
10
5 f---+r---,f---+---:f MAX
IDLE MODE
TYP(1)
L:::'d:=::±==t:=:J IDLE MODE

FREQ AT XTAL 1
Figure 13. ICC VB. FREQ

TYP(1) - See DC Electrical Characteristics
February 1989 2-48

Vee
Vee
Vee
RST
RST
(NC) XTAL2
(NC) XTAL2 CLOCK XTAL1 Vee
CLOCK XTAL1 SIGNAL Voo
SIGNAL Voo
Figure 14. Icc Test Condition, Active Mode Figure 15. Icc Test Condition, Idle Mode
0.45V
1-----tcLcL------"I
Figure 16. Clock Signal Waveform for IcC Tests in Active and Idle Modes
tCLCH =tCHCL =
5ns
Vee
RST
(NC) XTAL2
XTAL1 Vee
Voo

All other pins are disconnected. VCC = 2V to 5.SV
February 1989 2-49

+5V
Vee
A 0-A7 P1 PO PGM DATA

r
1 RST EAlVpp +12.75V
25 100us PULSES
1 P3.S ALE/PRciG TO GROUND
SC87C451
1 P3.7 PsEN o
XTAL2 P2.7
4-SMHz ~ =*=~ P2.S o
L =i=
XTAL1
P2.0
-P2.3 •
A
A8-A11
.-- Vss
- L-
J,....--------:25 PULSES----------01
i-----
ALE/PROG: -:LJLJlJUl.:::.------------
L-...,--J
1'- 10/iSMIN -01 r--- 100/iS±10-----1
ALE/PROG: ----o~I_______ __In n. . __

Figure 19. PROG Waveform
February 1989 2-50

+5V
Vee
AO-A7 -----,{I P1 PO I--""'-,{ PGM DATA

_ _ _-IjRST
EAlVpp ......- - -
----IjP3.6 ALE/PROO ......- - -
----IjP3.7 SC87C461 PSEN i t - - - - - 0
...--......---1 XTAL2 P2.7 i t - - - - - 0 (ENABLE)
P2.6 10---- 0
P2.0 1/'---- AS-A11

-P2.31\r----
-+-I XTAL1
L - _......
Voo
Figure 20. Programming Verification
EPROM PROGRAMMING AND VERIFICATION CHARACTERISTICS TA - 21°C to +27°C, VCC - 5V±10%, VSS - OV (see Figure 21)

Vpp Programming supply voltage 12.5 13.0 V
Ipp Programming supply current 50 rnA
1/tCLCL Oscillator frequency 4 6 MHz
tAVGL Address setup to PROG low 48tCLCL
tGHAX Address hold after PROG 48tcLCL
tDVGL Data setup to PROG low 48tCLCL
tGHDX Data hold after PROG 48tCLCL
tEHsH P2.7 (ENABLE) high to Vpp 48tCLCL
tSHGL Vpp setup to PROG low 10 ~
tGHSL Vpp hold after PROG 10 !IS

tGLGH PROG width 90 110 ~
tAVQV Address to data valid 48tCLCL

tELQV ENABLE low to data valid 48tCLCL
tEHQZ Data float after ENABLE 0 . 48tCLCL
tGHGL PROG high to PROG low 10 ~
February 1989 2-51

PROGRAMMING' VERIFICATION'
P1.0-P1.7 '\.
ADDRESS ADDRESS
P2.0-P2.3 /
-0 io- tAVOV
PORTO DATA IN DATA OUT

t DVGL
1-0 I- -0 I- tGHDX
t AVGL 25 PULSES
j.o---o ~ tGHAX
ALE/PROG h
tGLGH-o
t SHGL
D=-: 10- t GHGL
1--0 t GHSL
~
V
EANpp ~ LOGIC 1 LOGIC 1
- - -- - - - - - - - - - - -
LOGIC 0
- -- - - - - --
t EHSH
t EHOZ
P2.7
tELOr I-
EANBlE ---./
'FOR PROGRAMMING VERIFICATION SEE FIGURE 18.
FOR VERIFICATION CONDITIONS SEE FIGURE 20.
Figure 21. EPROM Programming and Verification
February 1989 2-52

8XC552 OVERVIEW DATA MEMORY
The internal data memory is divided into 3 sections: the

The 83C552 is a stand-alone high-performance micro-
lower 128 bytes of RAM, the upper 128 bytes of RAM
controller designed for use in real-time applications such
and the 128-byte special function register areas. The
as instrumentation, industrial control, and automotive
lower 128 bytes of RAM are directly and indirectly ad-
control applications such as engine management and
dressable. While RAM locations 128 to 255 and the spe-
transmission control. The device provides, in addition to
cial function register area share the same address space,
the 80C51 standard functions, a number of dedicated
hardware functions for these applications. they are accessed through different addressing modes.
RAM locations 128 to 255 are only indirectly address-
The 83C552 single-chip 8-bit microcontroller is manu- able and the special function registers are only directly
factured in an advanced CMOS process and is a deriva- addressable. All other aspects of the internal RAM are
tive of the 80C51 microcontroller family. The 83C552 identical to the 8051.
uses the powerful instruction set of the 80C51. Additional
special function registers are incorporated to control the The stack may be located anywhere in the internal RAM
on-chip peripherals. Three versions of the derivative ex- by loading the eight bit stack pointer. Stack depth is 256
ist although the generic term "83C552" is used to refer bytes maximum.
to family members:
SPECIAL FUNCTION REGISTERS
83C552: 8K bytes mask-programmable ROM, 256 bytes
The special function registers (directly addressable only)
RAM
contain all of the 83C552 registers except the program
87C552: 8K bytes EPROM, 256 bytes RAM counter and the four register banks. Most of the 56 spe-
cial function registers are used to control the on-chip
80C552: ROMless version of the 83C552 peripheral hardware. Other registers include arithmetic
registers (ACC, B, PSW), stack pointer (SP) and data
The 83C552 contains a non-volatile 8K x 8 read-only pointer registers (DHP, DPL). Sixteen of the SFR's
program memory, a volatile 256 x 8 read/write data contain 128 directly addressable bit locations. Table 8
memory, six 8-bit 110 ports, two 16-bit timer/event lists the 83C552's special function registers.
counters (identical to the timers of the 80C51), an addi-
tional 16-b~t timer coupled to capture and compare The standard 80C51 SFR's are present and function
latches, a fifteen-source, two-priority-level, nested inter- identically in the 83C552 except where noted in the fol-
rupt structure, an 8-input ADC, a dual DAC pulse width lowing sections.
modulated interface, two serial interfaces (UART and
I2C bus), a 'watchdog' timer and on-chip oscillator and TIMER T2
timing circuits. For systems that require extra capability,
Timer T2 is a 16-bit timer consisting of two registers
the 83C552 can be expanded using standard TIL com-
TMH2 (HIGH byte) and TML2 (LOW byte). The 16-bit
patible memories and logic.
timer/counter can be switched off or clocked via a
The 83C552 has two software selectable modes of re- prescaler from one of two sources: fosc/12 or an exter-
duced activity for further power reduction - Idle and nal signal. When Timer T2 is configured as a counter,
Power-down. The Idle mode freezes the CPU and resets the prescaler is clocked by an external signal on T2
Timer T2 and the ADC and PWM circuitry but allows (P1.4). A rising edge on T2 increments the prescaler
the other timers, RAM, serial ports and interrupt system and the maximum repetition rate is one count per ma-
to continue functioning. The Power-down mode saves the chine cycle (lMHz with a 12MHz oscillator).
RAM contents but freezes the oscillator causing all other
The maximum repetition rate for Timer T2 is twice the
chip functions to become inoperative.
maximum repetition rate for Timer 0 and Timer 1. T2
(P1.4) is sampled at S2P1 and again at S5P1 (i.e., twice
DIFFERENCES FROM THE 8051
per machine oycle). A rising edge is detected when T2
PROGRAM MEMORY is LOW during one sample and HIGH during the next
sample. To ensure that a rising edge is detected, the in-
The 83C552 contains 8K-bytes of on-chip program mem- put signal must be LOW for at least 1/2 cycle and then
ory which can be extended to 64K-bytes with external HIGH for at least 112 cycle. If a rising edge is detected
memories (see Figure 13). When the EA pin is held before the end of S2P1, the timer will be incremented
high, the 83C552 fetches instructions from internal ROM during the following cycle; otherwise it will be incre-
unless the address exceeds 1FFFH. Locations 2000H to mented one cycle later. The prescaler has a program-
FFFFH are fetched from external program memory. mable division factor of 1, 2, 4 or 8 and is cleared if its
When the EA pin is held low, all instructions fetches are division factor or input source is changed, or if the tim-
from external memory. ROM locations 0003H to 0073H er/counter is reset.
are used by interrupt service routines.
February 1989 2-53

(FF FFHI 64 K
(FFFFHI 64K ...-------,
EXTERNAL
(1 FFFHI
(20 OOHI 8192
8191
(
t
,
INTERNAL EXTERNAL (FFHI 255 ...-----<,
(EA. 11 (EA·OI
(7FHI 127
INTERNAL
DATA RAM (OOOOHI 0 '--_ _ _.....
(OOOOHI 0 (OOH) 0
~------~y~--------~ ~'--------~y~--------~ ~
PROGRAM MEMORY INTERNAL EXTERNAL
DATA MEMORY DATA MEMORY
Figure 13. Memory Map
Timer 1'2 may be read "on the fly", but possesses no

extra read latches and software precautions may have to
be taken to avoid misinterpretation in the event of an
overflow from least to most significant byte while Timer 6 4 I 0
1'2 is being read.· Timer 1'2 is not load able and is reset
by the RST signal or by a rising edge on ~e inp~t signal I
lEN (E8H) lenlECM2IECMIIECMOIEcr3IECT2IEcnlecrol
R1'2, if enabled. R1'2 is enabled by setting bIt 1'2ER MSB LSB
(TM2CON.5).
When the least significant byte of the timer overflows or BIT Symbol Function
\\hen a 16-bit overflow occurs, an interrupt request may
be generated. Either or both of these overflows can be lEN 1.7 ET2 Enable Timer T2 overflow interrupt( s)
programmed to request an interrupt. In both cases, the lENl.6 ECM2 Enable T2 Comparator 2 interrupt
IENl.5 ECMI Enable T2 Comparator I interrupt
interrupt vector will be the same. When the lower byte
IENl.4 ECMO Enable T2 Comparator 0 interrupt
(TML2) overflows, flag 1'2BO (TM2CON) is set and flag
lEN 1.3 ECf3 Enable T2 Capture register 3 interrupt
1'20V (TM2IR) is set when TMH2 overflows. These flags
IENl.2 ECT2 Enable T2 Capture register 2 interrupt
are set one cycle after an overflow occurs. Note that
IENl.l ECfI Enable T2 Capture register I interrupt
\\hen T20V is set, T2BO will also be set. To enable the
byte overflow interrupt, bits ET2 (IENl. 7, enable over-
IENl.O Ecro Enable T2 Capture register 0 interrupt
flow interrupt, see Figure 14) and 1'2lS0 (TM2CON.6,
byte overflow interrupt select) must be set. Bit T2BO
(TM2CON.4) is the Timer T2 byte overflow flag. Figure 14. Timer T2 Interrupt Enable Register (lEN1)
February 1989 2-54

Table 8. 8XC552 Special Function Registers

Direct Bit Address, Symbol or Alternative Port Function
Symbol Description Reset Value
Address MSB LSB
ACC* Accumulator EOH E7 E6 ES E4 E3 E2 E1 EO OOH
ADCH# A/D converter high C6H xxxxxxxxB
ADCON# Adc control CSH iADc.lIADc.0IADEX1ADCljADC~AADR2jAADR!lAAD~ xxOOOOOOB
B* B register FOH F7 F6 FS F4 F3 F2 Fl FO OOH
CTCON# Capture control EBH CTN31 CTP3 I CTN21 CTPZ ICTNll CTP ICTNO I CTPO OOH
CTH3# Capture high 3 CFH xxxxxxxxB
CTH2# Capture high 2 CEH xxxxxxxxB
CTHl# Capture high 1 CDH xxxxxxxxB
CTHO# Capture high 0 CCH xxxxxxxxB
CMH2# Compare high 2 CBH OOH
CMH1# Compare high 1 CAR OOH
CMHO# Compare high 0 C9H OOH
CTL3# Capture low 3 AFH xxxxxxxxB
CTL2# Capture low 2 AEH xxxxxxxxB
CTL1# Capture low 1 ADH xxxxxxxxB
CTLO# Capture low 0 ACH xxxxxxxxB
CML2# Compare low 2 ABH OOH
CML1# Compare low 1 AAH OOH
CMLO# Compare low 0 A9H OOH
DPTR: Data pointer (2 bytes)
IENO* Interrupt enable 0 A8H EA I EAD I ESlj ESO j ETlj EXlj ETO 1 ETl OOH
EF EE ED EC EB EA E9 E8
IENl*# Interrupt enable 1 E8H ET2 IECM21 ECMllECMO IECT31 ECTZI ECTl I ECTO OOH
IPO* Interrupt priority 0 B8H - I PAD I PSl I PSO I PTl I PXl I PTO I PXO xOOOOOOOB
FF FE FD FC FB FA F9 F8
IP1*# Interrupt priority 1 F8H PT2 1PCM21 PCMl LPCMol PCT3J PCTZ I PCTl I PCTO OOH
PS# Port S C4H ADC71ADC61ADCsIADC41ADC31ADC21ADCliADCO xxxxxxxxB
C7 C6 CS C4 C3 C2 Cl CO
P4*# Port 4 COH CMTlI CMTOlcMSRSlcMSR4IcMSR3lcMSR2lcMSRllcMSRO FFH
B7 B6 BS B4 B3 B2 B1 BO
P3* Port 3 BOH RD I WR I Tl I TO IINTlI INTO I TXD I RXD FFH
A7 A6 AS A4 A3 A2 Al AO
PZ* Port 2 AOH AlS I Al4 I A13 1 Al2 I All I AlO I A9 I A8 FFH
97 96 9S 94 93 92 91 90
Pl* Port 1 90H SDA I SCL I RT2j T2 j CT3Ij CTZlj CTlIj CTOI FFH
87 86 8S 84 83 82 81 80
PO* Port 0 80H AD7 I AD6 I ADS I AD4 I AD3 I AD2 I ADl I ADO FFH
PCON Power control 87H SMODI - I - I WLE I GFI I GFO I PD I IDL OOxxOOOOOB
D7 D6 DS D4 D3 D2 Dl DO
PSW· Program status word DOH CY I Ac.1 FO.1 RSlj RSOj OV L Fl 1 P OOH
PWMP# PWM prescaler FEH OOH
PWMl# PWM register 1 FDH OOH
PWMO# PWM register 0 FCH OOH
RTE# Reset/toggle enable EFH TP47 jTP46 I RP4Sj RP44 JRP431 RP42 IRP4l I RP40 OOH
SP Stack pointer 8lH 07H
SOBUF Serial 0 data buffer 99H xxxxxxxxB
* = SFRs are bit addressable.
# = SFRs are modified from or added to the 80CSl SFRs.
February 1989 2-55

Table 8. 8XC552 Special Function Registers (Continued)

Address MSB LSB
9F 9E 9D 9C 9B 9A 99 98
SOCON* Serial 0 control 98H SMO I SMI SM2 REN TB8 RB8 TI R1 OOH
SIADR# Serial I address DBH SLAVE ADDRESS GC OOH
SIDAT# Serial I data DAH OOH
SISTA# Serial I status D9H SC4j SC3 I SC2 I SCI 1 sco I 0 l 0 1 0 F8H
DF DE DD DC DB DA D9 D8
SICON#* Serial I control D8H - -.l ENSI STA STO SI AA CRI CRO xOOOOOOOB
STE# Set enable EEH TG47-.l TG46 I SP45 I SP44 I SP43 I SP42 L SP411 SP40 COH
THI Timer high I 8DH OOH

TLl Timer low I 8BH OOH
TMH2# Timer high 2 EDH OOH
TML2# Timer low 2 ECH OOH
TMOD Timer mode 89H GATE I CIT I MI I MO I GATE I CIT I MI I MO OOH
8F 8E 8D 8C 8B 8A 89 88
TCON* Timer control 88H TFI J TRI I TFO I TRO I IEI I IT! I lEO I ITO OOH
TM2CON# Timer 2 control EAH T2ISIJ TSISO I T2ER I T2BO I T2PI I T2PO IT2MSII T2MSO OOH
CF CE CD CC CB CA C9 C8
TM2IR# Timer 2 int flag reg C8H nov1 CMI2 I CMIl I CMIO I CTI3 I CTI2 j CTIll CTIO OOH
T3# Timer 3 FFH OOH
• = SFRs are bit addressable.
# = SFRs are modified from or added to the 80C51 SFRs.
To enable the 16-bit overflow interrupt, bits ET2 (IE1.7, OVINT: PUSH ACC ;save accumulator
enable overflow interrupt) and T2ISI (TM2CON.7, 16-bit PUSH PSW ;save status
overflow interrupt select) must be set. Bit T20V INC TIMEXI ;increment first
(TM2IR.7) is the Timer T2 16-bit overflow flag. All in- ; byte (low order)
terrupt flags must be reset by software. To enable both
;of extended timer
byte and 16-bit overflow, T2ISO and T2ISI must be set
and two interrupt service routines are required. A test on MOV A,TIMEXI
the overflow flags indicates which routine must be exe- JNZ INTEX ; jump to INTEX if
cuted. For each routine, only the corresponding overflow ;there is no
flag must be cleared. ; overflow
INC TIMEX2 ; increment second
Timer T2 may be reset by a nsmg edge on RT2 (Pl.5) ; byte
if the Timer T2 external reset enable bit (T2ER) in MOV A,TIMEX2
T2CON is set. This reset also clears the prescaler. In JNZ INTEX ; jump to INTEX i f
the Idle mode, the timer/counter and prescaler are reset ; there is no
and halted. Timer T2 is controlled by the TM2CON spe-
; overflow
cial function register (see Figure 15).
INC TIMEX3 ;increment third
Timer T2 Extension ; byte (high order)
INTEX: CLR T20V ;reset interrupt
When a 12MHz oscillator is used, a 16-bit overflow on ; flag
Timer T2 occurs every 65.5, 131, 262 or 524ms de- POP PSW ; restore status
pending on the prescaler division ratio i.e. the maximum POP ACC ;restore accumulator
cycle time is approximately 0.5 seconds. In applications RETI ; return from
where cycle times are greater than 0.5 seconds, it is
; interrupt
necessary to extend Timer T2. This is achieved by se-
lecting foscl12 as the clock source (set T2MSO, reset
Timer T2, Capture and Compare Logic
T2MSl), setting the prescaler division ratio to 118 (set
T2PO, set T2Pl), disabling the byte overflow interrupt Timer T2 is connected to four 16-bit capture registers
(reset T2ISO) and enabling the 16-bit overflow interrupt and three 16-bit compare registers. A capture register
(set T2ISl). The following software routine is written for may be used to capture the contents of Timer T2 when a
a three-byte extension which gives a maximum cycle transition occurs on its corresponding input pin. A com-
time of approximately 2400 hours. pare register may be used to set, reset or toggle Port 4
output pins at certain pre-programmable time intervals.
February 1989 2-56

sampled during SIP! of each cycle. When a selected

edge is detected, the contents of Timer 1'2 are captured
6 4 2 o at the end of the cycle.
TM2CON
(EAH)
I I I
11'21S1 1'2150 11'2ER 1'280 1'2PI I T2I'IlI 1'2MSII 1'2M5O I Measuring Time Intervals using Capture Registers
MSB LSB
When a recurring external event is represented in the
form of rising or falling edges on one of the four capture
pins, the time between two events can be measured using
Bit Symbol Functioa Timer 1'2 and a capture register. When an event occurs,
TM2CON.7 1'2ISI Timer 1'2 l6-bitoverflow intenuptselect the contents of Timer 1'2 are copied into the relevant
TM2CON.6 1'21S0 Timer 1'2 byte overflow intenupl select capture register and an interrupt request is generated.
TM2CON.5 1'2ER Timer 1'2 external reset enable. When this The interrupt service routine may then compute the in-
bit is set. Timer 1'2 may be reset by a rising terval time if it knows the previous contents of Timer 1'2
edge on R1'2 (PI.5). when the last event occurred. With a 12MHz oscillator,
TM2CON.4 1'280 Timer 1'2 byte overflow interrupt flag Timer 1'2 can be programmed to overflow every S24ms.
TM2CON.3
TM2CON.2
:g~ } Timer 1'2 prescaler select When event interval times are shorter than this, comput-
ing the interval time is simple and the interrupt service
routine is short. For longer interval times, the Timer 1'2
extension routine may be used.
T2P1 1'21'0 Timer 1'2 clock
0 0 clock source Compare Logic
0 I clock source/2
I 0 clock source,l4 Each time Timer 1'2 is incremented, the contents of the
I I clock sourcet8 three 16-bit compare registers CMO, CMl and CM2 are
compared with the new counter value of Timer 1'2. When
a match is found, the corresponding interrupt flag in
TM2CON.I 1'2MSI TM2IR is set at the end of the following cycle. When a
} Tuner 1'2 mode select match with CMO occurs, the controller sets bits 0-5 of
TM2CON.0 1'2MSO
Port 4 if the corresponding bits of the set enable register
STE are at logic 1. When a match with CMl occurs, the
controller resets bits 0-5 of Port 4 if the corresponding
1'2MSI T2MSO Mode selected bits of the reset/toggle enable register RTE are at logic
o o Timer 1'2 halted (oft) 1 (see Figure 18 for RTE register function). If RTE is
o I =
1'2 clock source f..J12 '0', then P4.n is not affect by a match between CMl or
I o Test mode; do not use CM2 and Timer 2. When a match with CM2 occurs, the
I I =
1'2 clock source pin 1'2 controller 'toggles' bits 6 and 7 of Port 4 if the corre-
sponding bits of the RTE are at logic 1. The port latch-
es of bits 6 and 7 are not toggled. Two additional flip-
Figure 15. T2 Control Register (TM2CON) flops store the last operation and it is these flip-flops
that are toggled. Thus, if the current operation is 'set',
The combination of Timer 1'2 and the capture and com- the next operation will be 'reset' even if the port latch is
pare logic is very powerful in applications involving rotat- reset by software before the 'reset' operation occurs. The
ing machinery, automotive injection systems, etc. Timer first 'toggle' after a chip RESET will set the port latch.
1'2 and the capture and compare logic are shown in Fig- The contents of these two flip flops can be read at
ure 16. STE.6 and STE.7 (corresponding to P4.6 and P4.7 re-
spectively). Bits STE.6 and STE.7 are read only (see
Capture Logic Figure 19 for STE register function). A logic 1 indicates
that the next toggle will set the port latch; a logic 0 in-
The four 16-bit capture registers that Timer 1'2 is con- dicates that the next toggle will reset the port latch.
nected to are: cro, crl, CI'2 and Cf3. These registers CMO, CMl and CM2 are reset by the RST signal.
are loaded with the contents of Timer 1'2 and an inter-
rupt is requested upon receipt of the input signals croI, The. modified port latch information appears at the port
crll, CI'2I or CI'3I. These input signals are shared with pin during SSP 1 of the cycle following the cycle in which
Port 1. The four interrupt flags are in the Timer 1'2 in- a match occurred. If the port is modified by software,
terrupt register (TM2IR special function register). If the the outputs change during S1Pl of the following cycle.
capture facility is not required, these inputs can be re- Each port 4 bit can be set or reset by software at any
garded as additional external interrupt inputs. time. A hardware modification resulting from a
comparator match takes precedence over a software
Using the capture control register crCON (see Figure modification in the same cycle. When the comparator
17), these inputs may capture on a rising edge, a falling results require a 'set' and a 'reset' at the same time, the
edge or on either a rising or falling edge. The inputs are port latch will be reset. .
February 1989 2-57

~r I~ I eTO
IT 1+11 eTl
IT eT2
I~:I ~r I~'I eT3
off
8 - bit overflow
interrupt
fose
I&-bit overflow
T2 .. interrupt
RT2
T2ER
external reset
enable
S R P4.0
S R P4.1
S R P4.2 INT
I/O port 4
S R P4.3~
S R P4.4 '\r--V
S R P4.S
TG T P4.&
TG T P4.7 5 • SIll T2 SFR address, TML2· lower 8 bits
R • reset TMH2· higher 8 bits
STE RTE
T • toggle
TG • toggle status
Figure 16. Block Diagram of Timer 2
7 6 4 2 o 7643210
~~H)ICIl3~1 erNj eml erN I CiPI C"3 aw I Rn (mf) I

11?4711P* 1aN'l __ RP431 aN21 aNI I I
RP40
MSB LSB MSB LSB

Bit S,mIIoI , Capture/lDterruptan: BIT Symbol Functloa
CTCON.7 CTN3 CapIUIe Register 3lriggeRd by a falling RTE.7 11'47 if 'I' then P4.7 toggles 01\ a march between
edge on CT31 CM2111d Tuner 1'2
CTCON:6 CI'P3 Capture Register 3 lriggeRd by a rising RTE.6 11'46 if 'I' then P4.6 toggles 011 • march between
edge 011 CT31 ,. CM21J1d Tuner 1'2
CTCON.S CTN2 Capture Register 2lriggeRd by a falling RTE.5 ItP45 if 'I' then P4.5 is reset an a march between
edge 011 CT21 CMIIJId Timer1'2
CTCON.4 CTP2, Capture Register 2lriggeRd by a rising RTE.4 RP44 if 'I' then P4.4 is reset 0111 march between
edgeOllCT21 CMIIJId Tuner 1'2
CTCON.3 CTNI Capture Register IlriggeRd by a falli", RTE.3 RP43 if 'I' then P4.3 is reset 011 1 mlk:b between
edge 011 CTII CMIIJId Timer 1'2
CTCON.2 CI1'I Capture Register 11riggeRd by a rising RTE.2 RP42 if 'I' then P4.2 is reset 011 1 march between
edge on CTII CMIIJId Timer 1'2
CTCON.I CTNO CapIUIe Register 0 IriggeRd by a fallin. RTE.I RP41 if 'I' then N.I is reset 011 1 march between
edge 01\ CTOI CMIIIId Timer 1'2
CTCON.O CTPO Capture Register 0 lrigered by a risi", RTE.O RP40 if 'I'lbea P4.0 is rae! 011 anwch between
edge 011 CTOI CMI IJId Tuner 1'2
Figure 17. Capture Control Register (CTCON) Figure 18, ReseVfoggle Enable Register (RTE)
February 1989 2-58

able period of time. An analogy is the "dead man's han-

765 432 1 0
dle" in railway locomotives. When enabled, the watchdog
STE (EEH) ITG471TG461SP451SP441SP431sP42jSP411sP40 circuitry will generate a system reset if the user program
MSB LSB fails to reload the watchdog timer within a specified
Bit Symbol length of time known as the 'watchdog interval'.
Function
STE.7 TG47 Toggle flip-flops
STE.6 TG46 Toggle flip-flops
STE.5 SP45 If '1' then P4.5 is set on a match be- 7 6 5 4 3 2 1 0
tween CMO and timer T2
STE.4 SP44 If '1' then P4.4 is set on a match be- M21R (C8H)IT20VICMI2ICMI1ICMIOI CTl31 CTI21 CTI1 I CTIO
tween CMO and timer T2 MSB LSB
STE.3 SP43 If '1' then P4.3 is set on a match be-
Bit Symbol Function
tween CMO and timer T2 TM2IR.7 T20V Timer T2 16-bit overflow interrupt flag
STE.2 SP42 If '1' then P4.2 is set on a match be- TM2IR.6 CMI2 CM2 interrupt flag
tween CMO and timer T2 TM2IR.5 CMI1 CM 1 interrupt flag
STE.1 SP41 If '1' then P4.1 is set on a match be- TM2IR.4 CMIO CMO interrupt flag
tween CMO and timer T2
TM2IR.3 CTI3 CT3 interrupt flag
STE.O SP40 If '1' then P4.0 is set on a match be- TM2IR.2 CTI2 CT2 interrupt flag
tween CMO and timer T2 TM2IR.1 CTI1 CT1 interrupt flag
Figure 19. Set Enable Register (STE) TM2IR.O CTIO CTO interrupt flag
Timer T2 Interrupt Flag Register TM2IR Interrupt Flag Register (TM2IR)
Eight of the nine Timer T2 interrupt flags are located in

special function register 1M2IR (see Figure 20). The 7 6 5 4 3 2 1 0
ninth flag is 1M2CON.4. IP1 (F8H) I PT2 IPCM21pCM11pCMOI PCT31 PCT21 PCT1I PCTO
MSB LSB
The CTOI and CTlI flags are set during S4 of the cycle
in which the contents of Timer T2 are captured. CTOI is Bit Symbol Function
IP1.7 PT2 Timer T2 overlfow interrupt(s) priority
scanned by the interrupt logic during S2 and CTlI is level
scanned during S3. CTII and CT3I are set during S6 IP1.6 PCM2 Timer T2 comparator 2 interrupt priority
and are sc anned during S4 and S5. The associated inter- level
rupt requests are recognized during the following cycle. IP1.5 PCM1 Timer T2 comparator 1 interrupt priority
If these flags are polled, a transition at CTOI or CTlI level
will be recognized one cycle before a transition on CTII IP1.4 PCMO Timer T2 comparator 0 interrupt priority
or CT3I since registers are read during S5. The CMIO, level
CMIl and CMI2 flags are set during S6 of the cycle fol- IP1.3 PCT3 Timer T2 capture register 3 interrupt
lowing a match. CMIO is scanned by the interrupt logic priority level
during S2; CMIl and CMI2 are scanned during S3 and IP1.2 PCT2 Timer T2 capture register 2 interrupt
priority level
S4. A match will be recognized by the interrupt logic (or IP1.1 PCT1 Timer T2 capture register 1 interrupt
by polling the flags) two cycles after the match takes priority level
place. IP1.0 PCTO Timer T2 capture register 0 interrupt
priority level
The 16-bit overflow flag (T20V) and the byte overflow
flag (T2BO) are set during S6 of the cycle in which the Timer 2 Interrupt Priority Register (IPi)
overflow occurs. These flags are recognized by the inter-
rupt logic during the next cycle.
Figure 20. Interrupt Flag Register (TM2IR)
and Timer T2 Interrupt Priority Register (IPl)
Special function register IP1 (Figure 20) is used to de-
termine the Timer T2 interrupt priority. Setting a bit
Watchdog Circuit Description
high gives that function a high priority, and setting a bit
low gives the function a low priority. The functions con- The watchdog timer (Timer T3) consists of an 8-bit tim-
trolled by the various bits of the IP1 register are shown er with an ll-bit prescaler as shown in Figure 21. The
in Figure 20. prescaler is fed with a signal whose frequency is 1/12
the oscillator frequency (1MHz with a 12 MHz oscilla-
TIMER T3, THE WATCHDOG TIMER
tor). The 8-bit timer is incremented every 't' seconds
where:
In addition to Timer T2 and the standard timers, a
watchdog timer is also incorporated on the 83C552. The
t = 12 x 2048 x lIfosc (= 2ms at fosc = 12MHz)
purpose of a watchdog timer is to reset the micro-
controller if it enters erroneous processor states (possi-
bly caused by electrical noise or RFI) within a reason-
February 1989 2-59

PRESCALER
11- BIT TIMER TJIB·BIT!
LOAD LOADEN
,.....
internal
writ~
T3 -~t----l -----c;:]
EWI
I -......- - - - - - - - " ' -_ _ _ _ _ _ _.. _-_-~~~_-_-_-__I -- '~f::'''
.....
INTERNAL BUS
Figure 21. Watchdog Timer
If the 8-bit timer overflows, a short internal reset pulse watchdog interval and thus it becomes more difficult to
is generated which will reset the 83CSS2. A short output implement watchdog operation.
reset pulse is also generated at the RST pin. This short
output pulse (3 machine cycles) may be destroyed if the The programmer must now partition the software in such
RST pin is connected to a capacitor. This would not, a way that reloading of the watchdog is carried out in
however, affect the internal reset operation. accordance with the above requirements. The program-
mer must determine the execution times of all software
Watchdog operation is activated when external pin EW is modules. The effect of possible conditional branches,
tied low. When EW is tied low, it is impossible to dis- subroutines, external and internal interrupts must all be
able watchdog operation by software. taken into account. Since it may be very difficult to
evaluate the execution times of some sections of code,
How to Operate the Watchdog Timer the programmer should use worst case estimations. In
any event, the programmer must make sure that the
The watchdog timer has to be reloaded within periods watchdog is not activated during normal operation.
that are shorter than the programmed watchdog interval;
otherwise the watchdog timer will overflow and a system The watchdog timer is reloaded in two stages in order to
reset will be generated. The user program must there- prevent erroneous software from reloading the watchdog.
fore continually execute sections of code which reload First, PCON.4 (WLE) must be set. Then T3 may be
the watchdog timer. The period of time elapsed between loaded. When T3 is loaded, PCON.4 (WLE) is auto-
execution of these sections of code must never exceed matically reset. T3 can not be loaded if PCON.4 (WLE)
the watchdog interval. When using a 12MHz oscillator, is reset. Reload code may be put in a subroutine as it is
the watchdog interval is programmable between 2ms and called frequently. Since Timer T3 is an up-counter, a
S1Oms. reload value of OOH gives the maximum watchdog inter-
val (S1Oms with a 12MHz oscillator) and a reload value
In order to prepare software for watchdog operation, a of OFFH gives the minimum watchdog interval (2ms with
programmer should first determine how long his system a 12MHz oscillator).
can sustain an erroneous processor state. The result will
be the maximum watchdog interval. As the maximum In the Idle mode, the watchdog circuitry remains active.
watchdog interval becomes shorter, it becomes more dif- When watchdog operation is implemented, the Power-
ficult for the programmer to ensure that the user pro- down mode cannot be used since both states are contra-
gram always reloads the watchdog timer within the dictory. Thus, when watchdog operation is enabled by ty-
February 1989 2-60

ing external pin EW low, it is impossible to enter the - Multimaster bus (no central master)
Power-down mode and an attempt to set the Power-down - Arbitration between simultaneously transmitting masters
bit (PCON.l) will have no effect. PCON.l will remain at without corruption of serial data on the bus
logic O. - Serial clock synchronization allows devices with differ-
ent bit rates to communicate via one serial bus
During the early stages of software development/debug- - Serial clock synchronization can be used as a hand-
ging, the watchdog may be disabled by tying the EW pin shake mechanism to suspend and resume serial trans-
high. At a later stage, EW may be tied low to complete fer
the debugging process. - The 12C bus may be used for test and diagnostic pur-
poses
Watchdog Software Example
The output latches of P1.6 and Pl.7 must be set to logic
The following example shows how watchdog operation 1 in order to enable SIal.
might be handled in a user program.
The 83C552 on-chip 12C logic provides a serial interface
;at the program start: that meets the 12C bus specification and supports all
transfer modes (other than the low speed mode) from
T3 EQU OFFH ;address of and to the I2C bus. The SIal logic handles bytes trans-
;watchdog timer T3 fer autonomously. It also keeps track of serial transfers,
PCON EQU 087H ;address of PCON SFR and a status register SlSTA) reflects the status of SIal
WATCH-INTV EQU 156 ;watchdog interval and the 12C bus.
;(e.g.2xlOOms)
ito be inserted at each watchdog reload The CPU interfaces to the I2C logic via the following
;location within the user program: four special function registers: SlCON (SIal control
register), SlSTA (SIOI status register), SlDAT (SIOI
LCALL WATCHDOG data register) and SlADR (SIal slave address register).
The Sial logic interfaces to the external 12C bus via
;watchdog service routine: two Port 1 pins: P1.6/SCL (serial clock line) and Pl.71
SDA (serial data line).
WATCHDOG: ORL PCON,tlOH;set condition A typic al 12C bus configuration is shown in Figure 22
; flag (PCON. 4) and Figure 23 shows how a data transfer is accomplished
MOV T3,WATCH-INV ;load T3 with on the bus. Depending on the state of the direction bit
; watchdog (R/W), two types of data transfers are possible on the
; interval 12C bus:
RET 1. Data transfer from a master transmitter to a slave
receiver. The first byte transmitted by the master is
If it is possible for this subroutine to be called in an er- the slave address. Next follows a number of data
roneous state, then the condition flag WLE should be set bytes. The slave returns an acknowledge bit after each
at different parts of the main program. received byte.
2. Data transfer from a slave transmitter to a master
SERIAL 110 receiver. The first byte (the slave address) is transmit-
ted by the master. The slave then returns an acknowl-
The 83C552 is equipped with two independent serial edge bit. Next follows a number of data bytes trans-
ports: SIOO and SIal. SIOO is a full duplex UART port mitted by the slave to the master. The master returns
and is identical to the 80C5l serial port. SIal accom- an acknowledge bit after all received bytes other than
modates the l2C bus. the last byte. At the end of the last received byte, a
'not acknowledge' is returned.
SIOO
The master device generates all of the serial clock puls-
SIOO is a full duplex serial I/O port identical to that on es and the START and STOP conditions. A transfer is
the 80C51. Its operation is identical including the use of ended with a STOP condition or with a repeated START
timer 1 as a baud rate generator.
condition. Since a repeated START condition is also the
beginning of the next serial transfer, the I2C bus will not
S101, Pc Serial 1/0 be released.
The 12C bus uses two wires (SDA and SCL) to transfer Modes of Operation
information between devices connected to the bus. The
main features of the bus are: The on-chip SIal logic may operate in the following
four modes:
- Bidirectional data transfer between masters and slaves
February 1989 2-61

VOD
) Rp ] Rp
SDA
SCL
Pl.7/SDA Pl.6/SCL
OTHER DEVICE OTHER DEVICE

83C552 WITH 12C WITH ,2C
INTERFACE 'NTERFACE
Figure 22. Typical Pc Bus Configuration
r-l
SOA~_-
STOP COndition
I __ J~-J~~_ _~
I I MSB
I I .,... odd,. .
I I
I I
I I
I I
I I
SCl~ r\ r\
i i \.J t \.J 2 L __
L..!.J
START
CONDiTION
Figure 23. Data Transfer on the 12C Bus
1. Master Transmitter Mode: 2. Master Receiver Mode:
Serial data output through P1.7/SDA while P1.6/SCL The first byte transmitted contains the slave address of
outputs the serial clock. The first byte transmitted con- the transmitting device (7 bits) and the data direction
tains the slave address of the receiving device (7 bits) bit. In this case the data direction bit (RJW) will be log-
and the data direction bit. In this case the data direction ic 1 and we say that an 'R' is transmitted. Thus the first
bit (RJW) will be logic 0 and we say that a 'W' is byte transmitted is SLA+R. Serial data is received via
transmitted. Thus the first byte transmitted is SLA+W. P1.7/SDA while P1.6/SCL outputs the serial clock. Se-
Serial data is transmitted 8 bits at a time. After each rial data is received eight bits at a time. After each byte
byte is transmitted, an acknowledge bit is received. is received, an acknowledge bit is transmitted. START
START and STOP conditions are output to indicate the and STOP conditions are output to indicate the beginning
beginning and the end of a serial transfer. and end of a serial transfer.
February 1989 2-62

3. Slave Receiver Mode: Comparator
Serial data and the serial clock are received through The comparator compares the received 7-bit slave ad-
P1.7/SDA and P1.6/SCL. After each byte is received, an dress with its own slave address (7 most significant bits
acknowledge bit is transmitted. START and STOP condi- in SlADR). It also compares the first received 8-bit
tions are recognized as the beginning and end of a serial byte with the general call address (OOH). If an equality
transfer. Address recognition is performed by hardware is found, the appropriate status bits are set and an inter-
after reception of the slave address and direction bit. rupt is requested.
4. Slave Transmitter Mode: Shift Register, SlDAT
The first byte is received and handled as in the slave re- This 8-bit special function register contains a byte of se-
ceiver mode. However, in this mode, the direction bit rial data to be transmitted or a byte which has just been
will indicate that the transfer direction is reversed. Se- received. Data in SlDAT is always shifted from right to
rial data is transmitted via P1.7/SDA while the serial left; the first bit to be transmitted is the MSB (bit 7)
clock is input through P1.6/SCL. START and STOP and, after a byte has been received, the first bit of re-
conditions are recognized as the beginning and end of a ceived data is located at the MSB of SlDAT. While data
serial transfer. is being shifted out, data on the bus is simultaneously
being shifted in; SlDAT always contains the last byte
In a given application, SIal may operate as a master present on the bus. Thus, in the event of lost arbitration,
and as a slave. In the slave mode, the SIal hardware the transition from master transmitter to slave receiver
looks for its own slave address and the general call ad- is made with the correct data in SlDAT.
dress. If one of these addresses is detected, an interrupt
is requested. When the microcontroller wishes to become Arbitration and Synchronization Logic
the bus master, the hardware waits until the bus is free
before the master mode is entered so that a possible In the master transmitter mode, the arbitration logic
slave action is not interrupted. If bus arbitration is lost checks that every transmitted logic 1 actually appears as
in the master mode, SIal switches to the slave mode a logic 1 on the 12C bus. If another device on the bus
immediately and can detect its own slave address in the overrules a logic 1 and pulls the SDA line low, arbitra-
same serial transfer. tion is lost and SIal immediately changes from master
transmitter to slave receiver. SIal will continue to out-
SI01 Implementation and Operation put clock pulses (on SCL) until transmission of the cur-
rent serial byte is complete.
Figure 24 shows how the on-chip 12C bus interface is
implemented and the following text describes the individ- Arbitration may also be lost in the master receiver
ual blocks. mode. Loss of arbitration in this mode can only occur
while SIal is returning a 'not acknowledge' (logic 1) to
Input Filters and Output Stages the bus. Arbitration is lost when another device on the
bus pulls this signal LOW. Since this can occur only at
The input filters have 12C compatible input levels. If the the end of a serial byte, SIal generates no further clock
input voltage is less than 1.5V, the input logic level is pulses. Figure 25 shows the arbitration procedure.
interpreted as 0; if the input voltage is greater than 3.0
V, the input logic level is interpreted as 1. Input signals The synchronization logic will synchronize the serial
are synchronized with the internal clock (fosc/4) and clock generator with the clock pulses on the SCL line
spikes shorter than three oscillator periods are filtered from another device. If two or more master devices gen-
out. erate clock pulses, the 'mark' duration is determined by
the device that generates the shortest 'marks' and the
The output stages consist of open drain transistors that 'space' duration is determined by the device that gener-
can sink 3mA at VOUT < O.4V. These open drain out- ates the longest 'spaces'. Figure 26 shows the synchroni-
puts do not have clamping diodes to VDD. Thus, if the zation procedure.
device is connected to the 12C bus and VDD is switched
off, the 12C bus is not affected. A slave may stretch the space duration to slow down the
bus master. The space duration may also be stretched
Address Register, SlADR for handshaking purposes. This can be done after each
bit or after a complete byte transfer. SIal will stretch
This 8-bit special function register may be loaded with the SCL space duration after a byte has been transmitted
the 7-bit slave address (7 most significant bits) to which or received and the acknowledge bit has been trans-
SIal will respond when programmed as a slave transmit- ferred. The serial interrupt flag (SI) is set and the
ter or receiver. The LSB (aC) is used to enable general stretching continues until the serial interrupt flag is
call address (DOH) recognition. cleared.
February 1989 2-63

r---,
r
I
--I'- ___
PI.7 :
....
I
I
I
P1.8/SCL
OUTPUT
STAGE
3
INPUT
'"...
-<
z
P1.1/SDA
I
FILTER
OUTPUT
.
a::
w
!:
STAGE
I
I
I r---, TIMER 1
OVERFLOW
L -+IL.. _Pl.8 I
_ _ ..J
STATUS {
BITS
SlSTA
Figure 24. Block Diagram of the 12C Bus Serial Interface
February 1989 2-64

I" ·1
,--_!_ll_1.....JrL-.-_-_l_'~_-=I====='f..== _ ____JX\___C
(3)
SDA l . . ____ ..J
SCL
--~ ACK
I. Another device transmits identical serial data

2. Another device overrules a logic I (dotted line) transmitted by SIOI (master) by pulling the SDA line LOW.
Arbitration is lost and SID 1 enters the slave receiver mode
3. SIOI is in the slave receiver mode but still generates clock pulses until the current byte has been transmitted.
SID I will not generate clock pulses for the next byte. Data on SDA originates from the new master once it has won
arbitration.
Figure 25. Arbitration Procedure
SDA ________~x~___________x==
SCL
I. Another sevice pulls the the SCL line low before the SIOI 'mark' duration is complete. The serial clock generator
is immediately reset and commences with the 'space' duration by pulling SCL LOW.
2. Another device stills pulls the SCL line LOW after SID I releases SCL. The serial clock generator is forced into the
wait state until the SCL line is released. ~
3. The SCL line is released and the serial clock generator commences with the mark duration.
Figure 26. Serial Clock Synchronization
February 1989 2-65

Serial Clock Generator Abbreviation Explanation

S Start condition
This programmable clock pulse generator provides the SLA 7-bit slave address
SCL clock pulses when SIOI is in the master transmitter R Read bit (high level at SDA)
or master receiver mode. It is switched off when SIOI is W Write bit (low level at SDA)
in a slave mode. The programmable output clock fre- A Acknowledge bit (low level at SDA)
quencies are: fosc/120, fosc/9600 and the Timer 1 over- A Not acknowledge bit (high level at SDA)
flow rate divided by eight. The output clock pulses have DATA S-bi t data byte
a 50% duty cycle unless the clock generator is synchro- p Stop condition
nized with other seL clock sources as described above.
In Figure 27-30, circles are used to indicate when the
Timing and Control serial interrupt flag is set. The numbers in the circles
show the status code held in the SlSTA register. At
The timing and control logic generates the timing and these points, a service routine must be executed to con-
control signals for serial byte handling. This logic block tinue or complete the serial transfer. These service rou-
provides the shift pulses for SlDAT, enables the tines are not critical since the serial transfer is sus-
comparator, generates and detects start and stop condi- pended until the serial interrupt flag is cleared by
tions, receives and transmits acknowledge bits, controls software.
the master and slave modes, contains interrupt request
logic and monitors the 12C bus status. When a serial interrupt routine is entered, the status
code in SlSTA is used to branch to the appropriate serv-
Control Register, SlCON ice routine. For each status code, the required software
action and details of the following serial transfer are
This 7-bit special function register is used by the micro- given in Tables 9-12.
controller to control the following SIOI functions: start
and restart of a serial transfer, termination of a serial Master Transmitter Mode
transfer, bit rate, address recognition and acknowledg-
ment. In the master transmitter mode, a number of data bytes
are transmitted to a slave receiver (see Figure 27). Be-
Status Decoder and Status Register fore the master transmitter mode can be entered,
SleON must be initialized as follows:
The status decoder takes all of the internal status bits
and compresses them into a 5-bit code. This code is
unique for each 12C bus status. The 5-bit code may be 7 6 5 4 3
used to generate vector addresses for fast processing of SlCON (DSH)
the various servic.e routines. Each service routine proc-
esses a particular bus status. There are 26 possible bus
states if all four modes of SIOI are used. The 5-bit stat-
us code is latched into the five most significant bits of
the status register when the serial interrupt flag is set CRO and CRI define the serial bit rate. ENSI must be
(by hardware) and remains stable until the interrupt flag set to logic 1 to enable SIOL If the AA bit is reset,
is cleared by software. The three least significant bits of SIOI will not acknowledge its own slave address or the
the status register are always zero. If the status code is general call address in the event of another device be-
used as a vector to service routines, then the routines coming master of the bus. In other words, if AA is reset,
are displaced by eight address locations. Eight bytes of SIOO can not enter a slave mode. STA, STO and SI
code is sufficient for most of the service routines (see must be reset.
the software example in this section).
The master transmitter mode may now be entered by set-
More Information on SI01 Operating Modes ting the STA bit using the SETB instruction. The SIOI
logic will now test the 12C bus and generate a start con-
The four operating modes are: dition as soon as the bus becomes free. When a START
condition is transmitted, the serial interrupt flag (S1) is
- Master Transmitter set and the status code in the status register (SlSTA)
- Master Receiver will be OSH. This status code must be used to vector to
Slave Receiver an interrupt service routine that loads SlDAT with the
- Slave Transmitter slave address and the data direction bit (SLA+W). The
S1 bit in Sl CON must then be reset before the serial
Data transfers in each mode of operation are shown in transfer can continue.
Figures 27-30. These figures contain the following ab-
breviations:
February 1989 2-66

MT
SUCCESSFUL TRANSMISSION
TO A SLAVE RECEIVER
NEXT TRANSFER STARTEO WITH

A REPEATEO START CONDITION
NOT ACKNOWLEDGE RECEIVED

AFTER THE SLAVE ADDRESS
TO MST/REC MODE
ENTRY. MR

AFTER A DATA BYTE
ARBITRATION LOST IN SLAVE

ADDRESS OR DATA BYTE
ARBITRATION LOST AND

ADDRESSED AS SLAVE
TO CORRESPONDING STATES
IN SLAVE MODE
~ FROM MASTER TO SLAVE
D FROM SLAVE TO MASTER
ANY NUMBER OF DATA BYTES

AND THEIR ASSOCIATED ACKNOWLEDGE BITS
THIS NUMBER (CONTAINED IN SlSTAI CORRESPONDS TO A

DEFINED STATE OF THE 12C·bus; See Table 9.
Figure 27. Format and States in the Master Transmitter Mode
February 1989 2-67

MR
SUCCESSFUL RECEPTION
FROM A SLAve
TRANSMITTER
NEXT TRANSFER STARTED WITH

R
A REPEATED START CONDITION

AFTER THE SLAVE ADDRESS
TO MST ITRX MODE

ENTRY -MT
ARBITRATION LOST IN SLAVE OTHER MST

ADDRESS OR ACKNOWLEDGE BIT CONTINUES
ARBITRATION LOST AND

ADDRESSED AS SLAVE
TO CORRESPONDING STATES
IN SLAVE MODE
r-;:;:~ ANY NUMBER OF DATA BYTES

L.::.:,,~ AND THEIR ASSOCIATED ACKNOWLEDGE BITS
8+ THIS NUMBER (CONTAINED IN SISTAI CORRESPONDS TO A

DEFINED STATE OF THE 12C-bus; See Tabla 10.
Figure 28. Format and States in the Master Receiver Mode
February 1989 2-68

RECEPTION OF THE OWN SLAVE

ADDRESS AND ONE OR MORE DATA
BYTES. ALL ARE ACKNOWLEDGED
LAST DATA BYTE RECEIVEO

IS NOT ACKNOWLEDGED
ARBITRATION LOST AS MST

AND ADDRESSED AS SLAVE
A
RECI:PTION OF THE GENERAL

CALL ADDRESS AND ONE OR
MORE DATA BYTES
LAST DATA BYTE IS NOT ACKNOWLEDGED
ARBITRATION LOST AS MST AND

ADDRESSED AS SLAVE BY GENERAL CALL []
c§
~ FROMMASTERTOSLAVE
~~
ANY NUMBER OF DATA BYTES
AND THEIR ASSOCIATED ACKNOWLEDGE BITS
8+ THIS NUMBER ICONTAINED IN SlSTAI CORRESPONDS TO A

Figure 29. Format and States in the Slave Receiver Mode
February 1989 2-69

RECEPTION OF THE OWN

SLAVE ADDRESS AND TRANSMISSION
OF ONE OR MORE DATA BYTES
ARBITRATION LOST AS MST

AND ADDRESSED AS SLAVE
D FROMSLAVETOMASTER
LAST DATA BYTE TRANSMIITEO.
SWITCHED TO NOT ADDRESSED
SLAVE (AA BIT IN SICON 0'0'1
~~ ANY NUMBER OF DATA BYTES
~~ AND THEIR ASSOCIATED ACKNOWLEDGE BITS
8+ THIS NUMBER (CONTAINED IN SISTAI CORRESPONDS TO A

Figure 30. Format and States of the Slave Transmitter Mode
When the slave address and the direction bit have been logic 1). The appropriate action to be taken for each of
transmitted and an acknowledgment bit has been re- these status codes is detailed in Table 10. ENS1, CR1
ceived, the serial interrupt flag (SI) is set again and a and CRO are not affected by the serial transfer and are
number of status codes in SlSTA are possible. There not referred to in Table 10. After a repeated start condi-
are 18H, 20H or 38H for the master mode and also tion (state 10H), SIal may switch to the master trans-
68H, 78H, or BOH if the slave mode was enabled (AA = mitter mode by loading SlDAT with SLA+W.
logic 1). The appropriate action to be taken for each of
these status codes is detailed in Table 9. ENS1, CR1 Slave Receiver Mode
and CRO are not affected by the serial transfer and are
not referred to in Table 9. After a repeated start condi- In the slave receiver mode, a number of data bytes are
tion (state lOH). SIal may switch to the master receiver received from a master transmitter (see Figure 29). To
mode by loading SlDAT with SLA+R. initiate the slave receiver mode. SlADR and SlCON
must be loaded as follows:
Master Receiver Mode
In the master receiver mode, a number of data bytes are 765 4 3 2 1 0

received from a slave transmitter (see Figure 28). The
transfer is initialized as in the master transmitter mode.
SlADR (DBH) !Xlxlxlxlxlxlx!ocl
- - - own slave address - - -
When the start condition has been transmitted, the inter-
rupt service routine must load SlDAT with the 7-bit The upper 7 bits are the address to which SIal will re-
slave address and the data direction bit (SLA+R). The
spond when addressed by a master. If the LSB (GC) is
SI bit in SlCON must then be cleared before the serial
set, SIal will respond to the general call address (OOR);
transfer can continue.
other wise it ignores the general call address.
When the slave address and the data direction bit have
been transmitted and an acknowledgment bit has been 7 6 5 4 3 210
received, the serial interrupt flag (SI) is set again and a SlCON (D8H)
number of status codes in SlSTA are possible. These
are 40H, 48H or 38H for the master mode and also
x 1 0 0 0 1 X X
68H, 78H, or BOH if the slave mode was enabled (AA =
February 1989 2-70

Table 9. Master Transmitter Mode
Status Status of the Application Software Response

Code PC bus and
(SISTA) SIO 1 Hardware ToSICON Next Action Taken by SIOI Hardware
To/From SlOAT
STA STO SI AA
08H A START condition Load SLA+W X 0 0 X SLA+W will be transmitted;
has been transmitted ACK bit will be received
10H A repeated START Load SLA+W or X 0 0 X As above
condition has been Load SLA+R X 0 0 X SLA+R will be transmitted;
transmitted SIOI will be switched to MST/REC
mode
18H SLA+W has been Load data byte or 0 0 0 X Data byte will be transmitted;
transmitted; ACK ACK bit will be received
has been received no SIDAT action or I 0 0 X Repeated START will be transmitted;
no S I DAT action or 0 I 0 X STOP condition will be transmitted;
STO nag will be reset
no SIDAT action I I 0 X STOP condition followed by a
START condition will be transmitted;
STO flag will be reset
20H SLA+W has been Load data byte or 0 0 0 X Data byte will be transmitted;
transmitted; NOT ACK bit will be received
ACK has been no SIDAT action or I 0 0 X Repeated START will be transmitted;
received no SIDATaction or 0 I 0 X STOP condition will be transmitted;
no SIDAT action 1 I 0 X STOP condition followed by a
28H Data byte in Load data byte or 0 0 0 X Data byte will be transmitted;
SI DAT has been ACK bit will be received
transmitted; ACK no SIDAT action or 1 0 0 X Repeated START will be transmitted;
has been received no SIDAT action or 0 I 0 X STOP condition will be transmitted;
no SIDAT action I I 0 X STOP condition followed by a
30H Data byte in Load data byte or 0 0 0 X Data byte will be transmitted;
SIDAT has been ACK bit will be received
transmitted; NOT no SIDAT action or I 0 0 X Repeated START will be transmitted;
ACK has been no SIDAT action or 0 1 0 X STOP condition will be transmitted;
received STO flag will be reset
no S I DA Taction I I 0 X STOP condition followed by a
38H Arbitration lost in No S 1DA T action or 0 0 0 X PC bus will be released;
SLA+R/Wor not addressed slave will be entered
Data bytes no SIDAT action I 0 0 X A START condition will be
transmitted when the bus becomes free
February 1989 2-71

Table 10. Master Receiver Mode

Code PC bus and
(SISTA) SlOl Hardware ToSlCON Next Action Taken by SlOl Hardware
To/From SlOAT
STA STO SI AA
08H A START condition Load SLA+R X 0 0 X SLA+R will be transmitted;

has been transmitted ACK bit will be received
IOH A repeated START Load SLA+R or X 0 0 X As above
condition has been Load SLA+W X 0 0 X SLA+W will be transmitted;
transmitted Sial will be switched to MST/TRX
mode
38H Arbitration lost in No Sl DAT action or 0 0 0 X FC bus will be released;
NOT ACK bit SI01 will enter a slave mode
no SlDAT action 1 0 0 X A START will be transmitted when
the bus becomes free
40H SLA+R has been No SlDAT action or 0 0 0 0 Data byte will be received;
transmitted; ACK NOT ACK bit will be returned
has been received no Sl DAT action 0 0 0 1 Data byte will be received;
ACK bit will be returned
48H SLA+R has been No S 1DA T action or 1 0 0 X Repeated START condition will be
transmitted; NOT transmitted
ACK has been no S 1DA T action or 0 1 0 X STOP condition will be transmitted;
received. STO flag will be reset
no SI DA Taction 1 1 0 X STOP condition followed by a
50H Data byte has been Read data byte or 0 I0 0 0 Data byte will be received;
received; ACK has I NOT ACK bit will be returned
been returned read data byte 0 0 0 1 Data byte will be received;
ACK bit will be returned
58B Data byte has been Read data byte or 1 0 0 X Repeated START condition will be
received; NOT ACK transmitted
has been returned read data byte or 0 1 0 X STOP condition will be transmitted;
read data byte 1 1 0 X STOP condition followed by a
February 1989 2-72

Table 11. Slave Receiver Mode

Status Statu. of the I'C bus Application Softwue IlelPOnle
Code and 510 I Hudware
(SISTA) ToSICON Next Action Taken by SI01 Hudwue
To/From SIDAT
STA STO SI AA
60H Own SLA+W has been No SIDATaction or X 0 0 0 Data byte will be received and NOT ACK will be returned
received; ACK has been no S I DATaction X 0 0 I Data byte will be received and ACK will be returned
returned
68H Arbitration lost in SLA+RtW No SIDAT action or X 0 0 0 Data byte will be received and NOT ACK will be returned
as master; Own SLA+W has no SIDAT action X 0 0 I Data byte will be received and ACK will be returned
been received, ACK returned
70H General call address (OOH) No S I DA T action or X 0 0 0 Data byte will be received and NOT ACK will be returned
has been received; ACK has no SIDATaction X 0 0 I Data byte will be received and ACK will be returned
been returned
78H Arbitration lost in SLA+R/W No SIDAT action or X 0 0 0 Data byte will be received and NOT ACK will be returned
as master; General call no SIDAT action X 0 0 I Data byte will be received and ACK will be returned
address has been received;
ACK has been returned
80H Previously addressed with Read data byte or X 0 0 0 Data byte will be received and NOT ACK will be returned
own SLY address; DATA read data byte X 0 0 I Data byte will be received and ACK will be returned
has been received; ACK has
been returned
88H Previously addressed with Read data byte or 0 0 0 0 Switched to not addressed SLV mode; no recognition
own SLA; DATA byte has of own SLA or General call address
been received; NOT ACK read data byte or 0 0 0 I Switched to not addressed SLV mode; Own SLA will
has been returned be recognized; General call address will be recognized
if SIADR. 0 =logic I
read data byte or I 0 0 0 Switched to not addressed SLV mode; no recognition
of own SLA or General call address. A START
condition will be transmitted when the bus becomes free.
read data byte I 0 0 I Switched to not addressed SLV mode; Own SLA will
be recognized; General call address will be recognized
if SIADR. 0 =logic 1. A START condition will be
transmitted when the bus becomes free.
90H Previously addressed with Read data byte or X 0 0 0 Data byte will be received and NOT ACK will be returned
General Call; DATA byte read data byte X 0 0 I Data byte will be received and ACK will be returned
has been received; ACK has
been returned
98H Previously addressed with Read data byte or 0 0 0 0 Switched to not addressed SLY mode; no recognition
General Call; DATA byte of own SLA or General call address
has been received; NOT ACK read data byte or 0 0 0 I Switched to not addressed SLY mode; Own SLA will
has been returned be recognized; General call address will be recognized
read data byte I 0 0 I Switched to not addressed SLV mode; Own SLA will
AOH A STOP condition or Read data byte or 0 0 0 0 Switched to not addressed SLY mode; no recognition
repeated START condition of own SLA or General call address
has been received while still read data byte or 0 0 0 I Switched to not addressed SLY mode; Own SLA will
addressed as SLV/REC or be recognized; General call address will be recognized
SLV/TRX if SIADR. 0 =logic I
read data byte I 0 0 I Switched to not addressed SLY mode; Own SLA will
February 1989 2-73

Table 12. Slave Transmitter Mode

Statu. Statu. of the PC bu. Application Software ReapOOIle
Code and SIOI Hudwue
(SISTA) ToSICON Next Action Taken by SIOI Hudwue
To/prom SIDAT
STA STO SI AA
ASH Own SLA+R has been Load data byte or X 0 0 0 Last data byte will be transmitted and
received; ACK bas been ACK bit will be received
returned load data byte X 0 0 I Data byte will be transmitted; ACK bit will be received
DOH Arbitration lost in SLA+R/W Load data byte or X 0 0 0 Last data byte will be transmitted and
as master; own SLA+R has ACK bit will be received
been received; ACK has been load data byte X 0 0 I Data byte will be transmitted; ACK bit will be received
returned
B8H Data byte in SlOAT has Load data byte or X 0 0 0 Last data byte will be transmitted and ACJ\ bi .. will be
been transmitted; ACK has load data byte X 0 0 I received Data byt~ will be tr.nsmilt~d: ACJ\ bit will be
been received received
COH Data byte in SlOAT bas No SIDAT aetion or 0 0 0 0 Switched to not addressed SLY mode; no recognition
been transmitted; NOT of own SLA or General call address
ACK has been received no SIOATaetion or 0 0 0 I Switched to not addressed SL V mode; Own SLA will
no S I OAT action or I 0 0 0 Switched to not addressed SLY mode; no recognition
no S I OAT action I 0 0 I Switched to not addressed SLV mode; Own SLA will
if SIADR. 0 =logic I. A START condition will be
CSH Last data byte in SlDAT No SIDAT action or 0 0 0 0 Switched to not addressed SLV mode; no recognition
hal been transmitted of own SLA or General call address
(AA =0); ACK has been no SlOAT action or 0 0 0 I Switched to not addressed SLV mode; Own SLA will
received be recognized; General call address will be recolnized
no S IDAT action or I 0 0 0 Switched to not addressed SLV mode; no recognition
no SlOAT action I 0 0 I Switched to not addressed SLV mode; Own SLA will
be recognized; General can address will be recolnized
If SIADR. 0 -lope I. A START condition will be
transmitted when the bUI becomes free.
CRO and CR1 do not affect SI01 in the slave mode. However, the I2C bus is still monitored and address rec-
ENS1 must be set to logic 1 to enable SIOl. The AA bit ognition may be resumed at any time by setting AA. This
must be set to enable SI01 to acknowledge its own slave means that the AA bit may be used to temporarily iso-
address or the general call address. STA, sm and SI late SI01 from the I2C bus.
must be reset.
Slave Transmitter Mode
When SlADR anq SlCON have been initialized, SI01
waits until it is addressed by its own slave address fol- In the slave transmitter mode, a number of data bytes
lowed by the data direction bit which must be '0' (W) for are transmitted to a master receiver (see Figure 30).
SI01 to operate in the slave receiver 'mode. After its Data transfer is initialized as in the slave receiver mode.
own slave address and the W bit have been received, the When SlADR and SlCON have been initialized, SI01
serial interrupt flag (I) is set and a valid status code can waits until it is addressed by its own slave address fol-
be read fromS1STA. This status code is used to vector lowed by the data direction bit which must be '1' (R) for
to an interrupt service routine and the appropriate action SI01 to operate in the slave transmitter mode. After its
to be taken for each of these status codes is detailed in own slave address and the R bit have been received, the
Table 11. The slave, receiver mode may also be entered serial interrupt flag (SI) is set and a valid status code
if arbitration is lost while SI01 is in the master mode can be read from SlSTA. This status code is used to
(see status 68H and 78H); vector to an interrupt service routine and the appropriate
action to be taken for each of these status codes is de-
If the AA bit is reset during a transfer ,SI01 will return tailed in Table 12. The slave transmitter mode may also
a not acknowledge (logic 1) to SDA after the next re- be entered if arbitration is lost while SI01 is in the mas-
ceived data byte. While AA is reset, SI01 does not re- ter mode (see state BOH).
spond to its own slave address or a general call address.
February 1989 2-74

If the AA bit is reset during a transfer, SIal will trans- set. To recover from a bus error, the STO flag must be
mit the last byte of the transfer and enter state COH or set and SI must be cleared. This causes SIal to enter
C8H. SIal is switched to the not addressed slave mode the 'not addressed' slave mode (a defined state) and to
and will ignore the master receiver if it continues the clear the STO flag (no other bits in SlCON are af-
transfer. Thus the master receiver receives all 1s as se- fected). The SDA and SCL lines are released (a STOP
rial data. While AA is reset, SIal does not respond to condition is not transmitted).
its own slave address or a general call address. How-
ever, the 12C bus is still monitored and address recogni- The Four SI01 Special Function Registers
tion may be resumed at any time by setting AA. This
means that the AA bit may be used to temporarily iso- The microcontroller interfaces to SIal via four special
late SIal from the I2C bus. function registers. These four SFR's (SlADR, SlDAT,
SlCON and SlSTA) are described individually in the fol-
Miscellaneous States lowing sections.
There are two SlSTA codes that do not correspond to a The Address Register, S1ADR
defined SIal hardware state (see Table 13). These are
discussed below. The CPU can read from and write to this 8-bit, directly
addressable SFR. SlADR is not affected by the SIal
SlSTA - F8H: hardware. The contents of this register are irrelevant
\Wen SIal is in a master mode. In the slave modes, the
This status code indicates that no relevant information is seven most significant bits must be loaded with the
available because the serial interrupt flag, SI is not yet microcontroller's own slave address and, if the least sig-
set. This occurs between other states and when SIal is nificant bit is set, the general call address (OOH) is rec-
not involved in a serial transfer. ognized; otherwise it is ignored.
SlSTA - OOH: 7 6 5 4 321 0
This status code indicates that a bus error has occurred

SlADR (DBH) Ixlxlxlxlxlxlxlocl
- - - own slave address - - -
during an SIal serial transfer. A bus error is caused
\Wen a START or STOP condition occurs at an illegal
position in the format frame. Examples of such illegal
positions are during the serial transfer of an address The most significant bit corresponds to the first bit re-
byte, a data byte or an acknowledge bit. A bus error may ceived from the 12C bus after a start condition. A logic
also be caused when external interference disturbs the 1 in SlADR corresponds to a high level on the I2C bus
internal SIal signals. When a bus error occurs, SI is and a logic 0 corresponds to a low level on the bus.
Table 13. Miscellaneous States

Code PC bus and
(SISTA) SIOI Hardware ToSICON Next Action Taken by SlOt Hardware
To/From SlOAT
STA STO SI AA
F8H No relevant state No SIDAT action No SICON action Wait or proceed current transfer.
information
available; Sl = 0
OOH Bus error during No SIDAT action 0 1 0 X Only the internal hardware is affected
MST or selected in the MST or addressed SL V modes.
slave modes, due to In all cases, the bus is released and
an illegal START or SIOI is switched to the not addressed
STOP condition. SLY mode. STO is reset.
State DOH can also
occur when
interf"rence causes
SI01 to enter an
undefined state.
February 1989 2-75

The Data RegIster, SIDAT Serial data is shifted out from SlDAT via a buffer
(BSD7) on the falling edges of clock pulses on the SCL
SIDAT contains a byte of serial data to be transmitted line.
or a byte which has just been received. The CPU can
read from and write to this 8-bit, directly addressable When the CPU writes to SlDAT, BSD7 is loaded with
SFR while it is not in the process of shifting a byte. This the content of SlDAT.7 which is the first bit to be
occurs when SIOI is in a defined state and the serial in- transmitted to the SDA line (see Figure 32). After nine
terrupt flag is set. Data in SlDAT remains stable as serial clock pulses, the eight bits in SlDAT will have
long as SI is set. Data in SlDAT is always shifted from been transmitted to the SDA line and the acknowledge
right to left: the first bit to be transmitted is the MSB bit will be present in ACK. Note that the eight transmit-
(bit 7) and, after a byte has been received, the first bit ted bits are shifted back into SlDAT.
of received data is located at the MSB of SlDAT. While
data is being shifted out, data on the bus is simultane- The Control RegIster, SICON
ously being shifted in; SlDAT always contains the last
data byte present on the bus. Thus, in the event of lost The CPU can read from and write to this 8-bit, directly
arbitration, the transition from master transmitter to addressable SFR. The most significant bit is not used
slave receiver is made with the correct data in SlDAT. and a logic 1 will be returned if SlCON.7 is read. Two
bits are affected by the SIOI hardware: the SI bit is set
\<hen a serial interrupt is requested and the STO bit is
7 654 3 210 cleared \<hen a STOP condition is present on the I2C
SlDAT (DAH) ISD7ISD6ISD5ISD4ISDJISDZISDlISDOI bus. The STO bit is also cleared when ENSI = '0'.
~--- shift direction - - - - - 76543210
SlCON (D8H) I - @NSllsTAlsTOI SI I AA ICRllCROI
SD7 - SDO:
8-bits to be transmitted or just received. A logic 1 in ENS1, the SIOI Enable Bit
SlDAT corresponds to a high level on the I2C bus and a
ENSI = '0': \<hen ENSI is '0', the SDA and SCI.. out-
logic 0 corresponds to a low level on the bus. Serial da-
puts are in a high impedance state. SDA and SCI.. input
ta shifts through SlDAT from right to left. Figure 31
signals are ignored, SIOl is in the 'not addressed' slave
shows how data in SlDAT is serially transferred to and
state and the STO bit in SlCON is forced to '0'. No
from the SDA line.
other bits are affected. P1.6 and P1.7 may be used as
SlDAT and the ACK flag form a 9-bit shift register open drain 1/0 ports.
\<hich shifts in or shifts out an 8-bit byte, followed by an
acknowledge bit. The ACK flag is controlled by the SIOI ENSI - '1': \<hen ENSI is '1', SIOI is enabled. The
P1.6 and PI. 7 port latches must be set to logic 1.
hardware and cannot be accessed by the CPU. Serial
data is shifted through the ACK flag into SlDAT on the
ENS!. should not be used to temporarily release SIOI
rising edges of serial clock pulses on the SCL line.
from the I2C bus since, when ENS1 is reset, the I2C bus
When a byte has been shifted into SlDAT, the serial da-
status is lost. The AA flag should be used instead (see
ta is available in SlDAT and the acknowledge bit is re-
description of the AA flag in the following text).
turned by the control logic during the ninth clock pulse.
In the following text, it is assumed that ENSI = '1'.
SOA
SCl
SHIFT PULSES
Figure 31. Serial Input/Output Configuration
February 1989 2-76

SOA 07 De 05 04 03 02 01 DO
SCc
SHIFT ACK &: 51 OAT SHiFT IN
'CK 121 121 121 121 121 121 121 121
121 121 121 121 121 121 121 111
SHIFT eS07 SHIFT OUT
BS01 07 06 05 04 03 02 01 DO III
LO .... OED BY THE CPu
(t) Valid data In StOAT

(2) Shifting data in S10AT and ACK
(3) High level on SOA
Figure 32. Shift-in and Shift-out Timing
STA, the START Flag ter mode (in a slave mode, SIal generates an internal
STOP condition which is not transmitted). SIal then
STA = '1': when the STA bit is set to enter a master transmits a START condition.
mode the SIal hardware checks the status of the 12C
bus and generates a START condition if the bus is free. STO = '0': when the STO bit is reset, no STOP condi-
If the bus is not free, then SIal waits for a STOP condition will be generated.
tion (which will free the bus) and generates a START
condition after a delay of a half clock period of the in- SI, the Serial Interrupt Flag
ternal serial clock generator.
SI = '1': when the SI flag is set, then, if the EA and
If STA is set while SIal is already in a master mode ES1 (interrupt enable register) bits are also set, a serial
and one or more bytes are transmitted or received, SIal interrupt is requested. SI is set by hardware when one of
transmits a repeated START condition. STA may be set 25 of the 26 possible SIal states is entered. The only
at any time. STA may also be set when SIal is an ad- state that does not cause SI to be set is state F8H which
dressed slave. indicates that no relevant state information is available.
STA = '0': when the STA bit is reset, no START condi- While SI is set, the low period of the serial clock on the
tion or repeated START condition will be geuerated. SCL line is stretched and the serial transfer is sus-
pended. A high level on the SCL line is unaffected by
STO, the STOP Flag the serial interrupt flag. SI must be reset by software.
STO = '1': when the STO bit is set while SIal is in a SI = '0': when the SI flag is reset, no serial interrupt is
master mode, a STOP condition is transmitted to the 12C requested and there is no stretching of the serial clock
bus. When the STOP condition is detected on the bus, on the SCL line.
the SIal hardware clears the STO flag. In a slave
mode, the STO flag may be set to recover from an error AA, the Assert Acknowledge Flag
condition. In this case, no STOP condition is transmitted
to the 12C bus. However, the. SIal hardware behaves as AA = '1': if the AA flag is set, an acknowledge (low
if a STOP condition has been received and switches to level to SDA) will be returned during the acknowledge
the defined 'not addressed' slave receiver mode. The clock pulse on the SCL line when:
STO flag is automatically cleared by hardware. -the 'own slave address' has been received
-the general call address has been received while the
If the STA and STO bits are both set, then a STOP con- general call bit (GC) in SlADR is set
dition is transmitted to the 12C bus if SIal is in a mas-
February 1989 2-77

-a data byte has been received while SIal is in the The Status Register, SISTA
master receiver mode
-a data byte has been received while SIal is in the ad- SlSTA is an 8-bit read-only special function register.
dressed slave receiver mode The three least significant bits are always zero. The five
most significant bits contain the status code. There are
AA = '0': if the AA flag is reset, a not acknowledge 26 possible status codes. When SlSTA contains FSH, no
(high level to SDA) will be returned during the acknowl- relevant state information is available and no serial in-
edge clock pulse on SCL when: terrupt is requested. All other SlSTA values correspond
-a data has been received while SIal is in the master to defined SIal states. When each of these states is en-
receiver mode tered, a serial interrupt is requested (SI = '1'). A valid
-a data byte has been received while SIal is in the status code is present in SlSTA one machine cycle after
addressed slave receiver mode SI is set by hardware and is still present one machine
cycle after SI has been reset by software.
When SIal is in the addressed slave transmitter mode,
state C8H will be entered after the last serial is trans- Some Special Cases
mitted (see Figure 30). When SI is cleared, SIal leaves
state C8H, enters the not addressed slave receiver mode The SIal hardware has facilities to handle the following
and the SDA line remains at a high level. In state C8H, special cases that may occur during a serial transfer:
the AA flag can be set again for future address
recognition. Simultaneous Repeated START Conditions
from 2 Masters
When SIal is in the not addressed slave mode, its own
slave address and the general call address are ignored. A repeated START condition may be generated in the
Consequently, no acknowledge is returned and a serial master transmitter or master receiver modes. A special
interrupt is not requested. Thus, SIal can be temporar- case occurs if another master simultaneously generates a
ily released from the I2C bus while the bus status is repeated START condition (see Figure 33). Until this
monitored. While SIal is released from the bus, START occurs, arbitration is not lost by either master since they
and STOP conditions are detected and serial data is were both transmitting the same data.
shifted in. Address recognition can be resumed at any
time by setting the AA flag. If the AA flag is set when If the SIal hardware detects a repeated START condi-
the part's own slave address or the general call address tion on the I2C bus before generating a repeated START
has been partly received, the address will be recognized condition itself, it will release the bus and no interrupt
at the end of the byte transmission. request is generated. If another master frees the bus by
generating a STOP condition, SI01 will transmit a nor-
CRO and CR1, the Clock Rate Bits mal START condition (state OSH) and a retry of the to-
tal serial data transfer can commence.
These two bits determine the serial clock frequency when
SIal is in a master mode. The various serial rates are Data Transfer After Loss of Arbitration
shown in Table 14.
Arbitration may be lost in the master transmitter and
A 12.5kHz bit rate may be used by devices that interface master receiver modes (see Figure 25). Loss of arbitra-
to the 12C bus via standard I/O port lines which are tion is indicated by the following states in SlSTA: 3SH,
software driven and slow. 100kHz is usually the maxi- 6SH, 78H and BOH (see Figures 27 and 2S).
mum bit rate and can be derived from a 12MHz oscilla-
tor or a 6MHz oscillator. A variable bit rate (0.5kHz to If the STA flag in SlCON is set by the routines which
62.5kHz) may also be used if Timer 1 is not required for service these states, then, if the bus is free again, a
any other purpose while SIal is in a master mode. START condition (state OSH) is transmitted without in-
tervention by the CPU and a retry of the total serial
The frequencies shown in Table 14 are unimportant when transfer can commence.
SIal is in a slave mode. In the slave modes, SIal will
automatically synchronize with any clock frequency up to
100kHz.
Table 14. Serial Clock Rates

CRI CRO fose divided by bit frequency
0 0 960 12.5 kHz@ fose =12 MH
0 I 120 100 kHz@ fo,", =12 MHz
I 0 60 100 kHz@ fo", =6 MHz
I I 96 x (256 - reload value of Timer I) 0.5 kHz to 62.5 KHz
(reload value range is 0 to 254 in mode 2) at fose = 12 MHz
February 1989 2-78

Forced Access to the I2C bus 12C Bus Obstructed by a Low Level on SCL or SDA
In some applications, it may be possible for an un- An 12C bus hang-up occurs if SDA or SCL is pulled
controlled source to cause a bus hang-up. In such situ- LOW by an uncontrolled source. If the SCL line is ob-
ations, tl,e problem may be caused by interference, tem- structed (pulled LOW) by a device on the bus, no further
porary interruption of the bus or a temporary short- serial transfer is possible and the SIal hardware cannot
circuit between SDA and SCL. resolve this type of problem. When this occurs, tllC prob-
lem must be resolved by tlw device that is pulling the
If an uncontrolled source generates a superfluous SCL bus line LOW.
START or masks a STOP condition, then tl,e I2C bus
stays busy indefinitely. If the STA flag is set and bus ac- If the SDA line is obstructed by another device on the
cess is not obtained within a reasonable amount of time, bus (e.g. a slave device out of bit synchronization), the
then a forced access to the 12C bus is possible. 11,is is problem can be solved by transmitting additional clock
achieved by setting the STO flag while the STA flag is pulses on the SCL line (see Figure 35). The SIal hard-
still set. No STOP condition is transmitted. The SIal ware transmits additional clock pulses when he STA flag
hardware behaves as if a STOP condition was received is set but no START condition can be generated because
and is able to transmit a START condition. The STO tl,e SDA line is pulled LOW while the 12C bus is con-
flag is cleared by hardware (see Figure 34). sidered free. The SIal hardware attempts to generate a
r---r----.,.-,-----.------.,----,----.- - - - - - - - - - ........ -~--~--
OTHER MST CONTINUES SLA

L-..--.L..-_--L_~~~ _ __'__.,...--'--.---L- _________ ..J...._...J...-.-...J..._ _
OTHER MASTER SENDS RETRY

REPEATED START
CONDITION EARLIER
Figure 33. Simultaneous Repeated START Conditions from 2 Masters
STAflag
I time limit
~---------l.-------------------
"I
STO flag __~Il~_______________

SDA line
1
sel line I
k--- START condition
Figure 34. Forced Access to a Busy PC Bus
February 1989 2-79

STA flag
-.J !(21 ! (31
SDA line tl l'O n

SCL line
START condition
(11 Unsuccessful attempt to send a START condition

121 SDA line released
(31 Succeuful attempt to send a START condition; state OB H is entered
Figure 35. Recovering from a Bus Obstruction Caused by a Low Level on SDA
START condition after every two additional clock pulses -The 26 state service routines for the
on the SCL line. When the SDA line is eventually re- -master transmitter mode
leased, a normal START condition is transmitted, state -master receiver mode
08H is entered and the serial transfer continues. -slave receiver mode
-slave transmitter mode
If a forced bus access occurs or a repeated START
condition is transmitted while SDA is obstructed (pulled Initialization
LOW), the SI01 hardware performs the same action as
described above. In each case, state 08H is entered af- In initialization routine, SI01 is enabled for both master
ter a successful START condition is transmitted and and slave modes. For each mode, a number of bytes of
normal serial transfer continues. Note that the CPU is internal data RAM are allocated to the SIO to act as ei-
not involved in solving these bus hang-up problems. ther a transmission or reception buffer. In this example
8 bytes of internal data RAM are reserved for different
Bus Error purposes. The data memory map is shown in Figure 36.
The initialization routine performs the following func-
A bus error occurs when a START or STOP condition is tions:
present at an illegal position in the format frame. Ex-
amples of illegal positions are during the serial transfer -SlADR is loaded with the part's own slave address and
of an address byte, a data or an acknowledge bit. the general call bit (GC)
-Pl.6 and Pl.7 bit latches are loaded with logic Is
The SIOI hardware only reacts to a bus error when it is -Ram location HADD is loaded with the high order
involved in a serial transfer either as a master or an ad- address byte of the service routines
dressed slave. When a bus error is detected, SIOI im- -The SIOI interrupt enable and interrupt priority bits
mediately switches to the not addressed slave mode, re- are set
leases the SDA and SCL lines, sets the interrupt flag -The slave mode is enabled by simultaneously setting
and loads the status register with OOH. This status code the ENSI and AA bits in SlCON and the serial clock
may be used to vector to a service routine which either frequency (for master modes) is defined by loading
attempts the aborted serial transfer again or simply re- CRO and CRI in SlCON. The master routines must be
covers form the error condition as shown in Table 13. started in the main program.
Software Examples of SIOl Service Routines The SIOI hardware now begins checking the 12C bus for
its own slave address and general call. If the general
This section consists of a software example for: call or the own slave address is detected, an interrupt is
requested and SlSTA is loaded with the appropriate
- Initialization of SIOI after a RESET state information. The following text describes a fast
-Entering the SIOI interrupt routine method of branching to the appropriate service routine.
February 1989 2-80

Specl" Function Reglstlrs
1 1
SlADR I GC DB
SlOAT DA
SlSTA I 0 I 0 I 0 09
SlCON X 1 ENSl I STA I STO I SI I AA I CRl I CRO 08
Internal DATA RAM
1
BACKUP ORIGINAL VALUE OF NUMBYTMST 53
NUMBYTMST NUM8ER OF BYTES AS MASTER 52
SLA SLA+R/W TO BE TRANSMITTED TO SLA 51
HADD HIGHER ADDRESS BYTE INTERRUPT ROUTINE 50
1
4F
SLAVE TRANSMITTER OATA RAM
STD r_________________________________ ~T4B
SRD1 SLAVE RECEIVER DATA RAM 1

T 40
1
MRD _
MASTER RECEIVER DATA RAM 1
T 38
MTD1 MASTER TRANSMITTER DATA RAM 1

130
IT : [:
_________________________~Too
~
Figure 36. 8101 Data Memory Map
February 1989 2-81

SI01 Interrupt Routine 28. In the example below, 4 bytes are transferred. There
is no repeated START condition. In the event of lost ar-
When the SI01 interrupt is entered, the PSW is first bitration, the transfer is restarted when the bus becomes
pushed on the stack. Then SlSTA and HADD (loaded free. If a bus error occurs, the I2C bus is released and
with the high order address byte of the 26 service rou- SI01 enters the not selected slave receiver mode. If a
tines by the initialization routine) are pushed on to the slave device returns a not acknowledge, a STOP condi-
stack. SlSTA contains a status code which is the lower tion is generated.
byte of one of the 26 service routines. The next instruc-
tion is RET which is the return from subroutine instruc- A repeated START condition can be included in the se-
tion. When this instruction is executed, the high and low rial transfer if the STA flag is set instead of the STO
order address bytes are popped from stack and loaded flag in the state service routines vectored to by status
into the program counter. codes 28H and 58H. Additional software must be written
to determine which data is transferred after a repeated
The next instruction to be executed is the first instruc- START condition.
tion of the state service routine. Seven bytes of program
code (which execute in eight machine cycles) are re- Slave Transmitter and Slave Receiver Modes
quired to branch to one of the 26 state service routines.
After initialization, SI01 continually tests the 12C bus
SI PUSH PSW Save PSW and branches to one of the slave state service routines if
PUSH SISTA Push status code it detects its own slave address or the general call ad-
(low order address byte) dress (see Table 11, Table 12, Figure 29, and Figure
PUSH HADD Push high order address 30). If arbitration was lost while in the master mode, the
master mode is restarted after the current transfer. If a
byte
bus error occurs, the 12C bus is released and SI01 en-
RET Jump to state service ters the not selected slave receiver mode.
routine
In the slave receiver mode, a maximum of 8 received
The state service routines are located in a 256-byte page data bytes can be stored in the internal data RAM. A
of program memory. The location of this page is defined maximum of 8 bytes ensures that other RAM locations
in the initialization routine. The page can be located any- are not overwritten if a master sends more bytes. If
where in program memory by loading data RAM register more than 8 bytes are transmitted, a not acknowledge is
HADD with the page number. Page 01 is chosen in this returned and SI01 enters the not addressed slave re-
example and the service routines are located between ceiver mode. A maximum of one received data byte can
addresses OlOOH and 01FFH. be stored in the internal data RAM after a general call
address is detected. If more than one byte is transmitted,
The State Service Routines
a not acknowledge is returned and SI01 enters the not
addressed slave receiver mode.
The state service routines are located 8 bytes from each
other. 8 bytes of code are sufficient for most of the serv-
In the slave transmitter mode, data to be transmitted is
ice routines. A few of the routines require more than 8
obtained from the same locations in the internal data
bytes and have to jump to other locations to obtain more
RAM that were previously loaded by the main program.
bytes of code. Each state routine is a part of the SI01
After a not acknowledge has been returned by a master
interrupt routine and handles one of the 26 states. It
receiver device, SI01 enters the not addressed slave
ends with a RETI instruction which causes a return to
mode.
the main program.
Adapting the Software for Different Applications
Master Transmitter and Master Receiver Modes
The following software example shows the typical struc-
The master mode is entered in the main program. To
ture of the interrupt routine including the 26 state serv-
enter the master transmitter mode, the main program
ice routines and may be used as a base for user applica-
must first load the internal data RAM with the slave ad-
tions. If one or more of the four modes are not used, the
dress, data bytes and the number of data bytes to be
associated state service routines may be removed but
transmitted. To enter the master receiver mode, the
care should be taken that a deleted routine can never be
main program must first load the internal data RAM
invoked.
with the slave address and the number of data bytes to
be received. The RlW bit determines whether SI01 op- This example does not include any time-out routines. In
erates in the master transmitter or master receiver the slave modes, time-out routines are not very useful
mode.
since, in these modes, SI01 behaves essentially as a
passive device. In the master modes, an internal timer
Master mode operation commences when the STA bit in
may be used to cause a time-out if a serial transfer is
SlCION is set by the SETB instruction and data transfer
not complete after a defined period of time. This time
is controlled by the master state service routines in ac-
period is defined by the system connected to the 12C bus.
cordance with Table 9, Table 10, Figure 27 and Figure
February 1989 2-82

!***********************************************************
1 SIOl EQUATE LIST
1***********************************************************
!***********************************************************
1 LOCATIONS OF THE SIOl SPECIAL FUNCTION REGISTERS
1***********************************************************
0008 SlCON -oxd8
0009 SlSTA -Oxd9
OOOA SlDAT -Oxda
000& SlADR -Oxdb
00A8 IENO -axa8
00&8 IPO -Oxb8
1***********************************************************
I&IT LOCATIONS
1***********************************************************
OODD STA -Oxdd ISTA bit in SlCON
OO&D SIOIHP -oxbd IIPO, SIOl Priority bit
1***********************************************************
!IMMEDIATE DATA TO YRITE INTO REGISTER SICON
1***********************************************************
00D5 ENSI NOTSTA STO NOTSI AA CRO -Oxd5 !Genearates STOP
- - - - - ! (CRa-lOO Khz)
00C5 ENSl_NOTSTA_NOTSTO_NOTSI_AA_CRO -Oxe5 !Releases SUS and
!ACK
OOCl !Releases SUS and
!NOT ACK
00E5 -Oxe5 IRelease SUS and
Iset STA
1***********************************************************
IGENERAL IMMEDIATE DATA
1***********************************************************
0031 OWNSLA -Ox31 IOwn SLA+Cenerall Call
Imust be written into SlADR
OOAO ENSIOI -OxaO !EA+ESl, enable SIOl interrupt
lmust be written into IENO
0001 PAGI -ax01 Iseleet PAGI as HADD
OOCO SLAW -oxeO ISLA+W to be transmitted
OOCl SLAR -oxel ISLA+R to be transmitted
0018 SElJtB3 -ox18 ISeleet Register Rank 3
1***********************************************************
ILOCATIONS IN DATA RAM
!***********************************************************
0030 HTD -Ox30 !KST/TRX/DATA base address
0038 KRD -Ox38 IKST/REC/DATA base address
0040 SRD -Ox40 ISLV/REC/DATA bas. address
0048 STD -Ox48 ISLV/TRX/DATA bas. address
0053 MCKUP -Ox53 I&aekup from NUHBYTHST.
!To restore NUKBYTHST in case
!of an Arbitration Lost.
0052 NUHBYTHST-Ox52 !Number of bytes to transmit
lor receive as KST.
0051 SLA -Ox5l IContains SLA+R/W to be
I transmitted.
0050 HADD -Ox50 IHigh Address byte for STATE 0
!till STATE 25.
February 1989 2-83

1******************************·········********************
IINITIALISATION ROUTINE
IExample to initialize IIC Interface as slave receiver or
Islave transmitter and start a KASTER TRANSMIT or a KASTER
IRECEIVE function. 4 bytes will be transmitted or received.
I*********************************~*********************
.sect strt
.base OXOO
0000 4100 ajmp INIT I RESET
.sect initial
.base Ox200
0200 75DB31 INIT: mov SlADR,tI'OWNSLA I Load own SLA + enable
Igeneral call recognition
0203 D296 setb pl(6) IPl.6 High level.
0205 D297 setb pl(7) IPl.7 High level.
0207 755001 mov HADD,.PAGI
020A 43A8AO orl IENO,.ENSIOI !Enable 5101 interrupt
020D C2BD clr SIOIHP 15101 interrupt low
Ipriority
020F 75D8C5 mov SlCON,"'ENSl NOTSTA NOTSTO NOTSI AA CRO
- - IInitlalize-SLV funct.
1************************************************************
! •••....••.•.•.•.•••••••••••••••.•••••••.•...••••••.••••.•...
!START KASTER TRANSMIT FUNCTION
I· .......................................................... .
0212 755204 mov NUMBYTMST,.Ox4 !Transmit 4 bytes.

0215 7551CO mov SLA .• SLAW ISLA+W,Transmit funct.
0218 D2DD setb STA Iset STA in SlCON
I··· ....................•....................•...............
!START KASTER RECEIVE FUNCTION
1····································-·······_····_·-· ... _-_.
02lA 755204 mov NUMBYTMST,.Ox4 IReceive 4 bytes.
021D 7551Cl mov SLA ••SLAR !SLA+R, Receive funct.
0220 D2DD setb STA Iset STA in SlCON
1····_··········_··········_···········-······ __ ···_·· .... _.-
February 1989 2-84

!~""""*************************************************
! SIOl INTERRUPT ROUTINE
!***********************************************************
.sect intvec
.base Ox2b !SIOl interrupt vector
!SlSTA and HADD are pushed onto the stacK. They serve as
!return address for the RET instruction.
!The RET instruction sets the Program Counter to address
!HADD,SlSTA and jumps to the rigth subroutine.
002B CODO push psw !save plW

002D COM push SlSTA
002F COSO push HADD
0031 22 ret ! JKP to address
!HADD,SlSTA.
!-----------------------------------------------------------
! STATE: 00, Bus error.
! ACTION: Enter not adressed SLV aode and release bus.
! STO reset.
!-----------------------------------------------------------
.sect stO
.base OxlOO
0100 75D8D5 aov SlCON,.ENS1 NOTSTA STO NOTSI AA CIl0 !clr SI

- - - - - !set STO,AA
0103 DODO pop psw
0105 32 reti
February 1989 2-85

1***********************************************************
1*********************········******************************
IKASTER STATE SERVICE ROUTINES
1***********************************************************
IState 08 and State 10 are both for KST/TRX and KSTjREC.
IThe R/W bit decides whether the next state 1s within
IKST/TRX mode or within KSTjREC mode.
1********········*******************************************
I ..................•..•.•.........•....•....................
I STATE: 08, A START condition ha. been transmitted.
I ACTION: SLA+R/W are transmitted, ACK bit is received.
I·····················································".'"
.• ect at.8
.bue Oxl08
0108 855lDA mov SlOAT ,SLA ILoad SLA+R/W

OlOB 7508C5 mov SlCON,_ENSl NOTSTA NOTSTO NOTSI AA CRO
- - Iclr SI - -
OlOE OlAO ajmp INITBASEl
t····················································· ..... .
I STATE: 10, A repe.ted START condition has been
I transmitted.
I ACTION: SLA+R/W are transmitted, ACK bit 1s received.
! ....... - .................................................. ,
.• ect mUlO
.base Ox110
0110 8551DA mov S1DAT,SlA !Load SLA+R/W

0113 7508C5 aov SlCON,_ENSl_NOTSTA NOTSTO NOTSI AA CRO
Iclr SI
0116 OlAO ajlllp INITBASEI
.• ect ibase1
.base OxaO
OOAO 750018 INITBASE1: mov psw,_SEUU!3
00A3 7930 mov rl,_KTD
00A5 7838 aov rO,_KRO
00A7 855253 mov BACKUP, NUKBYTHST ISave initial value
OOAA DODO pop psw
OOAC 32 ret!
February 1989 2-86


1***********************************************************
1***********************************************************
IMASTER TRANSMITTER STATE SERVICE ROUTINES
1***********************************************************
!***********************************************************
I .......................................................... .
I STATE: l8.Previous stste was STATE 8 or STATE 10.
I SLA+W have been transmitted. ACK ha.
I been received.
1 ACTION: First DATA i. transmitted. ACK bit
I 1. recieved.
I····················································· ..... .
.• ect IIts18
.ba.. Ox118
0118 75D018 1I0Vpsw._SELRB3
0118 87DA 1I0VSlDAT.@rl
011D 0185 ajmp CON
I· ......................................................... .
STATE : 20. SLA+W have been transmitted. NOT ACK
has been received
ACTION: Transmit STOP condition.
I· ......................................................... .
. sect mts20
.base Ox120
0120 75D8D5 1I0V SlCON._ENS1_NOTSTA_STO_NOTSI_AA_CRO

Iset STO, clr SI
0123 DODO pop psw
0125 32 reti
1················································_···· ..... .
I STATE: 28. DATA of SlDAT have been transmitted
I ACK received.
ACTION: If Transmitted DATA i. last DATA then
transmit a STOP condition, else transmit
I next DATA.
I····················································· ..••..
. sect mt.28
.base Ox128
0128 D55285 djnz NUMBYTMST.NOTLDATl IJMP if NOT last DATA
0128 75D8D5 mov SlCON._ENSl NOTSTA STO NOTSI AA CRO
- - -Iclr SI.-set AA
012E 0189 ajmp RETmt
.sect mts28sb
.base OxObO
0080 75D018 NOTLDATl: mov psw._SELRB3
0083 87DA 1I0V SlDAT.@rl
0085 75D8C5 CON: mov SlCON._ENSl NOTSTA NOTSTO NOTSI AA CRO
- - !clr SI.-elr AA
0088 09 inc rl
0089 DODO RETmt pop psw
0088 32 retl
February 1989 2-87


1-- - - - -- -- - - -- - - - - - - - - -- - --- - - - -- - - -- - - - - - - - --- - - - - - - - - - - - -_
I STATE: 30, DATA of SlOAT have been transmitted,
I NOT ACK received.
I ACTION: Transmi t a STOP condition.
1·---------------------------------------------------------
. sect mts30
.
.base Ox130
0130 750805 mov SlCON,_ENSl NOTSTA STO NOTSI AA CRO
- - -Iset STO~ c1r SI
0133 0000 pop psw
0135 32 reti
1-----------------------------------------------------------
STATE: 38, Arbitration lost in SLA+W or OATA.
ACTION: Bus is released, not adressed SLV mode is
entered. A new START condition is transmitted
when the lIC bus is free again. .
1-----------------------------------------------------------
.sect mta38
.base Ox138
0138 7508E5 mov SlCON,_ENSl STA NOTSTO NOTSI AA CRO

Ol3B 855352 mov NUKBYTKST,BACKUP - --
013E 01B9 ajmp RETmt
1***********************************************************
!***********************************************************
!MASTER RECEIVER STATE SERVICE ROUTINES
1***********************************************************
!***********************************************************
1-----------------------------------------------------------
STATE : 40, Previoua state was STATE 08 or STATE 10,
SLA+R have been transmitted, ACK received.
I ACTION: OATA will be received, ACK returned.
1-----------------------------------------------------------
.sect mrs40
.base Ox140
0140 7508C5 mov SlCON,_ENSl NOTSTA NOTSTO NOTSI AA CRO

- - Iclr 5TA,STO~5I set AA
0143 OlCB ajmp RETmr
! - - - - - -- - -- - - - - - -- - - --- ---- -- - - - - -- - --- - - - - - -- - - - - - - - - - -- _.-

STATE: 48, SLA+R have been transmitted, NOT ACK
received.
! ACTION: STOP condition will be generated.
! - - - ---- - - - - - --- -- - -- - - -- - --- --- - - - --- - --- -- - --- -- - - - - - - - - --
.sect mrs48
.base Ox148
0148 750805 STOP: mov 51CON,_EN51 NOTSTA STO NOT5I AA CRO

- - -Iset STO~ clr 51
Ol4B 0000 pop psw
0140 32 reti
February 1989 2-88


I························· ................................. .
I STATE : 50, DATA have been received, ACK returned.
I ACTION: Read DATA of SlDAT.
I DATA will be received, if it i. la.t
I DATA then NOT ACK wil be returned el.e ACK
I will be returned.
I······························ ...••.....•.....•••..........
. Iect m.SO
.ba.e Ox150
0150 75D018 aov psw,.SEutB3
0153 A60A aov @rO,SlOAT IRead received OATA
0155 OlCO ajap RECl
••ect an501
.ba.e OxcO
OOCO 055205 REC1: djnz NUKBYTKST,NOTLDAT2
00C3 7508Cl aov SlCON,.ENSl NOT5TA NOTSTO NOTSI NOTAA CRO
- - !clr 5I,M -
00C6 8003 Ijap RETllr
00C8 7508CS NOTLDAT2: aov SlCON,IJEN51 NOTSTA NOT5TO NOTSI AA CRO
- - !crr SI,-set AA
OOCB 08 RETIIr: inc rO
OOCC DODO pop paw
OOCE 32 reti
I.·······.··.·.··· •. · ........ ·· .. · ......................... .

I STATE : 58, OATA have been received, NOT ACK
I returned.
! ACTION: Read DATA of SlDAT and ,enerate a STOP
I condition.
I········· .•.•.•••...••••••••••••••••.•••••....•.•..••..•••.
.•ect arlS8
.ba.e Ox158
0158 750018 aov p.w,.SEutB3
015B A60A _v @rO, SlOAT
0150 80E9 ajap STOP
February 1989 2-89


1***********************************************************
1***********************************************************
I SLAVE RECEIVER STATE SERVICE ROUTINES
1***********************************************************
1***********************************************************
I ......................................~··········· ........ .
I STATE : 60, Own SLA+W have been received,ACK
I returned.
I ACTION: DATA will be received and ACK returned.
I····················································· ..... .
.• ect .rs60
.base Ox160
0160 7508C5 mov SlCON,ilIENSI NOTSTA NOTSTO NOTSI AA eRO
- - Iclr SI, iet-AA
0163 750018 mov psw,ilISElJt.B3
0166 0100 ajmp INITSRD
.aect insrd
.baae OxdO
0000 7840 INITSRD: mov rO,ilISRD
00D2 7908 mov rl,ilI8
0004 0000 pop psw
0006 32 retl
I····················································· ..•.••
I STATE: 68, Abitratlon lost in SLA and R/W as MST
Own SLA+W have been received, ACK returned
ACTION: DATA will be received and ACK returned.
STA 1s set to restart MST mode after the
I bus is free again.
I···············~-············--------·---···-···--··- ..... .
. aect srs68
.baae Ox168
0168 7508E5 mov SlCON ,ilIENSl STA NOTSTO ROTSI AA eRO
016B 750018 mov psw,ilISElJt.B3- - - --
016E 0100 ajmp INITSRD
! ......•...•......•...•..•••••••.• __ ... _.........••...•.....
STATE : 70, General call has been received, ACK
returned.
! .............................. _---_ .•...............•......
. sect sra70
.base Ox170
0170 7508C5 mov SlCON,ilIENSl NOTSTA NOTSTO NOTSI AA CRO
- - Iclr SI, iet-AA
0173 750018 mov psw,ilISElJt.B3 IInitialize SRD counter
0176 0100 ajmp INITSRD
I································---·--··-····~······· ..... .
STATE: 78, Arbitration lost in SLA+R/W as MST.
eeneral call has been received, ACK returned ..
STA is set to restart KST mode after the
1·································_·······_··········· ..... .
• sect sra78
.base Oxl78
0178 7508E5 mov SlCON,ilIENSl_STA_NOTSTO_NOTSI_AA_CRO
017B 750018 mov psw,ilISElJt.B3 IInitialize SRD counter
017E 0100 ajmp INITSRO
February 1989 2-90

1--------------------------------------------- ________ ------
I STATE : SO, Previou.ly .ddre •• ed with own SLA.
I DATA receiv.d, ACK r.turn.d.
I ACTION: r ••d DATA.
I IF r.ceiv.d DATA w.. the l •• t THEN .uperfluou.
I DATA will be r.c.iv.d .nd NOT ACK returned ELSE
I next DATA will b. r.c.iv.d .nd ACK returned.
1-----------------------------------------------------------
.••ct .nSO
.b••• OxlSO
0180 7500lS _v p.w,.SELllB3
OlB3 A6DA aov @rO,SlDAT IRe.d r.c.ived DATA
OlB5 OlDS .jap IlEC2
.•ect snSO•
• b ••• OxdB
OODS D906 IlEC2: dj nz rl, NOTLDAT3

OODA 75DSCl LOAT: aov SlCON,.ENSl MOTSTA MOTSTO MOTSI MOTAA CRO
- - Icrr SI,iA -
OODD DODO pop p.w
OODF 32 reti
OOEO 75DSC5 MOTLDAT3: aov SlCON,_ENSl NOTSTA NOTSTO MOTSI AA CRO
- - Icrr SI,-.ee AA
00E3 OS inc rO
00E4 DODO RET.r: pop p.w
00E6 32 r.ti
1-----------------------------------------------------------
ISTATE : SS, Previously .dr••••d with own SLA.
I DATA r.c.iv.d NOT ACK r.turned.
ACTION: No ••v. of DATA, Enter NOT .dr••••d SLV
aode. R.cognition of own SLA. G.ner.l c.ll
I r.cogniz.d, if SlADR.G-l.
1-----------------------------------------------_··----.--..
.••ct .r.SS
.b••e OX18S
01S8 75D8C5 aov SlCON,.ENSl NOTSTA NOTSTO NOTSI AA CRO

- - - Iclr Sl, •• t AA
OlBll 01E4 .jap RETsr
\---_._. __ ._--_ .. _-----------------_._-_ .. _... _---_._._.- ...
\ STATE : 90, Previously .ddr••••d with gener.l c.ll.
I DATA h.s b.en r.c.iv.d, ACK h•• b•• n r.turn.d.
I ACTION: Re.d DATA.
Aft.r Gener.l c.ll only one byte will be
I r.c.ived with ACK the •• cond DATA will be
I rec.iv.d with NOT ACK.
\ DATA will b. r.c.iv.d and NOT ACK
\ r.turned.
\--_ .. _------_._._---------_. __ ._._--_ -.-_
... _--_._ .... .....
.••ct .r.gO
.ba.e Ox190
0190 7500lS aov p.w,.SEJ..aJ3
0193 A6DA aov @rO,SlDAT IRead received DATA
0195 OlDA ajap LOAT
February 1989 2-91


I .....••....................•......••.•.....•...... ··· ..... .
I STATE: 98, Previou.1y .dr•••• d vith ,.nera1 call.
I DATA baa b••n r.cdv.d, lOT ACK baa be.n
I r.turned.
I ACTION: No ••v. of DATA. Enter NOT .dr•••• d SLV
I aode. a.coanition of own SLA: a.n.ra1 call
I recoanized, if SlADR.G-1.
I····················································· ..... .
•••ct .rd8
.ba.e Ox198
0198 7SD8CS .ov SlCON,_ERSl NOTSTA IIOTSTO NOTSl AA eRO
- - IcIr SI,-••t AA
0198 DODO pop paw
019D 32 ret!
1·_··································-···············-.-.".
I STATE : AD, A STOP condition or r.p•• t.d START has
I b•• n r.ceiv.d, while still .dr••••d as
I SLV/llEC or SLV/TRX.
, ACTION: No ••ve of DATA, Enter lOT .drea.ed SLV
I .od•. Recognition of own SLA. a.nera1 call
I recoanized, if SlADR.G-l.
1-··············· __ ·················-··_··········_··· ..... .
••• ct .rsAO
.base Ox1aO
OlAO 75D8C5 aov SlCON, _ERSI NOTSTA NOTSTO NOTSI AA eRO
- - IClr SI: .et M
OlA3 DODO pop psw
OlA5 32 ret!
February 1989 2-92


1***********************************************************
1***********************************************************
I SlAVE TRANSKITIER STATE SERVICE ROUTINES
1***********************************************************
1***********************************************************
1----------------------------------------- ____________ ------
I STATE: A8, Own SlA+R received, ACK returned.
I ACTION: DATA viII be transaittad, A bit recaived.
1-----------------------------------------------------------
.sect stsa8
.base Oxle8
OlAB BS48DA aov SlDAT,STD Iload DATA in SlDAT

0lA! 7SD8CS aov SlCON,_ENSl NOTSTA NOTSTO NOTSI AA eRO
- - Iclr SI,-set AA
OlAE 01E8 ajap INITBASE2
... ct ib.. e2
.base Oxe8
00E8 75D018 INITBASE2: IDOV psv,_SELR.B3
OOEll 7948 IDOV rl, _STD
OOED 09 inc rl
OOEE DODO pop psv
OOFO 32 retl
1-----------------------------------------------------------
STATE: BO, Arbitration lost in SlA and RfW as KST.
Own SlA+R received, ACK returned.
ACTION: DATA viII be transmitted, A bit received.
STA is set to restart KST mode after the
1-----------------------------------------------------------
.sect stsbO
.ba.e OxlbO
OlIO 8548DA IDOVSlDAT,STD !load DATA in SlOAT
OlB3 7SD8E5 IDOVSICON,_ENSl STA NOTSTO NOTSl AA CRO
OlB6 01E8 ajmp INITBASE2 - - - --
1-----------------------------------------------------------
I STATE: B8, DATA ha. been tran.aitted,ACK received.
I ACTION: DATA viII be tran.mitted. ACK bit is received.
1-- -- - - - - -- -- -- - - - - - -- - - -- - -- -- -- - -- - - - - - - - - - - -- - - - - - - - - - - --
.• ect stsb8
.base Oxlb8
01B8 75D018 mov psv •• SELR.B3

OlU 870A mov SlDAT.@rl
OlBO 0lF8 ejmp SCON
.sect sen
.base Oxf8
00F8 75D8C5 SCON: mov SlCON •• ENSl NOTSTA NOTSTO NOTSI AA CRO
- - - Iclr SI, set AA
OOFB 09 inc rl
OOFC DODO pop psv
OOFE 32 retl
February 1989 2-93


I····················································· ..... ~
I STATE : CO, DATA has b •• n tranaaltt.d, NOT ACK
I r.c.lv.d.
I ACTION: Ent.r not .dr•••• d SLV mode.
I····················································· ..... .
.•• ct .t.cO
.b••• OxlcO
OICO 750aC5 aov SlCON ,«IINSl NOTSTA NOTSTO NOTSI AA CRO
- - - Iclr 51 .•et AA
OlC3 DODO pop p.w
01C5 32 utl
I···········~········································· ..... .
I STATE: ca. La.t DATA b •• b ••n tr.naaltt.d (AA-o).
I ACK r.c.lv.d.
I ACTION: Ent.r not .dr•••• d SLV mode.
I.· .... ·· .. ·· ... · .•• • .••• ·.· .. ··· ...... ··•· ... ····.··· ..... .
.•• ct .ue8
.b••• OxleS
OlC8 7508C5 aov SlCON ,«lENS 1 NOTSTA NOTSTO NOTSI AA CRO
- - - I elr 51, •• t AA
OlC! 0000 pop p.w
OICO 32 uti
1**************···*·*·**···**······*·**··***·*···***********
lEND OF 5101 INTERRUPT ROUTINE
1***··*··*·*·*·***·**·*·***····****·************************
1************"*******************************'*************
February 1989 2-94

RESET CmCUITRY set external devices this capacitor arrangement should

not be connected to the RST pin, and a different circuit
The reset circuitry for the 83C552 is connected to the should be used to perform the power-on reset operation.
reset pin RST. A Schmitt trigger is used at the input for A Timer T3 overflow, if enabled, will force a reset con-
noise rejection (see Figure 37). The output of the dition to the 83C552 by an internal connection, whether
Schmitt trigger is sampled by the reset circuitry every the output RTS is tied LOW or not.
machine cycle.
The internal reset is executed during the second cycle in
which RST is HIGH and is repeated every cycle until
Voo RST goes low. It leaves the internal registers as follows:
overflow Register Content

...-l1L...----r------- timer T3
ACC 0000 0000
SCHMITT AOCON xxOO 0000
TRIGGER
ADCH xxxx xxxx
RESET B 0000 0000
RST--t".....-i CIRCUITRY CMLO-CML2 0000 0000
on·chlp CMHO-CMH2 0000 0000
resistor creON 0000 0000
CfLO-cn...3 xxxx xxxx
CTHO-CTH3 xxxx xxxx
Figure 37. On-Chip Reset Configuration DPL 0000 0000
DPH 0000 0000
A reset is accomplished by holding the RST pin HIGH IENO 0000 0000
for at least two machine cycles (24 oscillator periods) IENl 0000 0000
while the oscillator is running. The CPU responds by ex- IPO xOOO 0000
ecuting an internal reset. During reset ALE and PSEN
output a HIGH level. In order to perform a correct re-
!PI 0000 0000
set, this level must not be affected by external elements. PCH 0000 0000
The RST line can also be pulled HIGH internally by a PCL 0000 0000
pull-up transistor activated by the watchdog timer T3. PCON OxxO 0000
The length of the output pulse from T3 is 3 machine cy- PSW 0000 0000
cles. A pulse of such short duration is necessary in order PWMO 0000 0000
to recover from a processor or system fault as fast as PWMI 0000 0000
possible. PWMP 0000 0000
PO-P4 1111 1111
Note that the short reset pulse from Timer T3 cannot P5 xxxx xxxx
discharge the power-on reset capacitor (see Figure 38). RTE 0000 0000
Consequently, when the watchdog timer is also used to re- SOBUF xxxx xxxx
SOCON 0000 0000
Voo SIADR 0000 0000
SICON xOOO 0000
SlOAT 0000 0000
vooJ SISTA 1111 1000
+ SP 0000 0111
2.2 I'F!~
80C552 STE 1100 0000
83C552 TCON 0000 0000
87C552 THO,THI 0000 0000
AST TMH2 0000 0000
TLO, TI..1 0000 0000
TML2 0000 0000
AAST TMOD 0000 0000
TM2CON 0000 0000
TM2IR 0000 0000
T3 0000 0000
The internal RAM is not affected by reset. At power-on,

Figure 38 Power-On Reset the RAM content is indeterminate.
February 1989 2-95

INTERRUPTS detailed below along with the specifics of the interrupts

unique to the 83C552.
The 83C552 has fifteen interrupt sources, each of which
can be assigned one of two priority levels, as shown in The eight Timer TI interrupts are generated by flags
Figure 39. The five interrupt sources common to the CTIO-CT13 , CMIO-CMI2 and by the logical OR of flags
80C5I are the external interrupts (INTO and INTI), the TIOV and T2B0. Flags CTIO to CT13 are set by input
timer 0 and timer I interrupts (ITO and ITI) and the se- signals CTO! to CT3!. Flags CMIO to CMI2 are set
rial I/O interrupt (RI or TI). In the 83C552, the stan- when a match occurs between Timer TI and the com-
dard serial interrupt is called SIOO. Since the subsys- pare registers CMO, CM1 and CM2. When an 8-bit or
tems which create these interrupts are identical on both 16-bit overflow occurs, flags TIBO and TIOV are set re-
parts, their functionality is likewise identical. The only spectively. These nine flags are not cleared by hardware
differences are the locations of the enable and priority and must be reset by software to avoid recurring
register configurations and the priority structure. This is interrupts.
interrupt enable registers

interrupt interrupt priority
--
sources source enable global enable registers
-
polling hardware
r--
INTO EXTERNAL ~r- ,I ,I
INTERRUPT
REQUEST 0 "- I' "0- r- ,2 bl
r-
12C ~ r- bl
cl
SERIAL dl
PORT
f-- " I'
~ r- b2 01
AOC
- 0- cl
11
f--
"" I'
~- c2
91
TIMER 0
..... ,... - 0- dl hI
OVERFLOW
r-- -=::
-
-
d2 ;]
high
pnoritv
interrupt
TIMER 2
...... ,... 0- 01 jl request
~-
CAPTURE 0 02 k1
f-- 11
TIMER 2
,... - 0- 11
ml
~ --
COMPARE 0
"' 12
- f-- n1
INT1 EXTERNAL
INTERRUPT ...... ,... 0- 91 01
---- vector
REOUEST 1
r-- ~ -- 0-
92
hI
SOURCE
IDENTIFICATION
TIMER 2
CAPTURE 1
-- ,... 1 "0- - h2
r-- ,2
TIMER 2
,... -0- ;1
b2
~ --
COMPARE 1
:---
" ,2 c2
TIMER 1 0- jl d2
1 "0- -
OVERFLOW
"'
r--
I" j2 02
TIMER 2 0-
- kl
12
92
CAPTURE 2
"- 1"0- i-- k2
TIMER 2
COMPARE 2
r-
...... ,... 0-
-- 11
h2
;2 low
priority
-
12
I-- 1"0- j2 interrupt
UART I T request
t'-.. ,... 0- ml k2
SERIAL 1--
V ......
~ r- n 1
PORT I R i-- m2 12
r-- m2
TIMER 2
CAPTURE 3 ...... ,... 1
0-
"0- r- n2
n2
r-- 02
TIMER T2 t'....
......
0- r - 01 ----SOURCE
vector
OVERFLOW V
-" -
Figure 39. The Interrupt System
----"o-r- 02 IDENTIFICATION
February 1989 2-96

The ADC interrupt is generated by the ADCI flag in the

ADC control register (ADCON). This flag is set when 6 4 o
an ADC conversion result is ready to be read. ADCI is IENI (ESH)
not cleared by hardware and must be reset by software to
avoid recurring interrupts. MSB LSB
The SI01 (12C) interrupt is generated by the SI flag in Bit Symbol Functioa
the SIOI control register (SlCON). This flag is set when
SlSTA is loaded with a valid status code.
lEN 1.7 En Enable n overllow intelTUpt(s)
lEN 1.6 ECM2 Enable n comparator 2 interrupt
lEN 1.5 ECMI Enable n comparator I interrupt
The ADCI flag may be reset by' software. It cannot be lEN 1.4 ECMO Enable n comparator 0 interrupt
set by software. All other flags that generate interrupts IENl.3 ECT3 Enable n capture register 3 intelTUpt
may be set or cleared by software and the effect is the lEN 1.2 ECT2 Enable n capture register 2 interrupt
same as setting or resetting the flags by hardware. Thus, IENl.l ECTI Enable n capture register I interrupt
interrupts may be generated by software and pending in- lEN 1.0 ECTO Enable n capture register 0 interrupt
terrupts can be cancelled by software.
In all cases, if the enable bit is '0', then the interrupt is disabled and
Interrupt Enable Registers if the enable bit is 'I', then the interrupt is enabled.
Each interrupt source can be individually enabled or dis- Figure 41. Interrupt Enable Register (lENt)
abled by setting or clearing a bit in the interrupt enable
special function registers IENO and IEN1. All interrupt 7 6 4 o
sources can also be globally enabled or disabled by set-
ting or clearing bit EA in IENO. The interrupt enable
registers are described in Figures 40 and 41.
MSB LSB
Interrupt Priority Structure
Bit Symbol Function
Each interrupt source can be assigned one of two prior-
ity levels. Interrupt priority levels are defined by the in- IP.7 Unused
terrupt priority special function registers IPO and IP1. IP.6 PAD AOC intelTUpt priority level
IPO and IP1 are described in Figure 42 and 43. IP.5 PS I SIO I (lle) intelTUpt priority level
IP.4 PSO Sioo (UART) interrupt priority level
Interrupt priority levels are as follows: 1P.3 PTI Timer I interrupt priority level
'0' - low priority IP.2 PX I External interrupt I priority level
'1' - high priority IP.I PTO Timer 0 interrupt priority level
IP.O PXO External interrupt 0 priority level
6 4 o
IENO (ASH) I I IESI I IETI IEXI I I I
EA EAD ESO ETC EXO
Figure 42. Interrupt Priority Register (lPO)
MSB LSB
Bit Symbol Function

7 6 5 4 3 2 I 0
IENO.7 EA Global enable/disable control

o= No interrupt is enabled
IPI (FSH)
I PI< IPCM21 PCMII KMOI I
KTI Pen IPeril K"l1) I
I = Any individually enabled interrupt will be
accepted Bit Symbol Function
IENO.6 EAD Enable AOC interrupt
IENO.S ESI Enable SIO I (lle) interrupt 1P1.7 PT2 n overflow interrupt(s) priority level
IENO.4 ESO Enable Sloo (UART) interrupt IPI.6 PCM2 n comparator 2 interrupt priority level
IENO.3 ETI Enable Timer I intelTUpt 1P1.S PCMI n comparator I interrupt priority level
IENO.2
IENO.I
EXI Enable External interrupt I 1P1.4 PCMO n comparator 0 interrupt priority level
IENO.O
ETO
EXO
Enable Timer 0 interrupt IP1.3 PCT3 n capture register 3 interrupt priority level
Enable External interrupt 0 1P1.2 PCT2 12 capture register 2 interrupt priority level
Figure 40. Interrupt Enable Register (lENO)
IPI.I PCTI n capture register I interrupt priority level
IPI.O PCTO n capture register 0 interrupt priority level
Figure 43. Interrupt Priority Register (lP1)
February 1989 2-97

A low priority interrupt may be interrupted by a high blocking condition is removed, then the blocked interrupt
priority interrupt. A high priority interrupt cannot be in- will not be serviced. Thus, the fact that the interrupt flag
terrupted by any other interrupt source. If two requests was once active but not serviced is not remembered.
of different priority occur simultaneously, the high prior- Every polling cycle is new.
ity level request is serviced. If requests of the same pri-
ority are received simultaneously, an internal polling se- The processor acknowledges an interrupt request by exe-
quence determines which request is serviced. Thus, with- cuting a hardware-generated LCALL to the appropriate
in each priority level, there is a second priority structure service routine. In some cases it also clears the flag
determined by the polling sequence. This second priority which generated the interrupt, and in others it does not.
structure is shown in Table 15. It clears the Timer 0, Timer 1 and external interrupt
flags. An external interrupt flag (lEO or lEI) is cleared
Table IS. Interrupt Priority Structure only if it was transition-activated. All other interrupt
flags are not cleared by hardware and must be cleared
Source Name Priority Within Level by the software. The LCALL pushes the contents of the
External interrupt 0 XO (highest) program counter on to the stack (but it does not save the
SIOl (I2C) Sl PSW) and reloads the PC with an address that depends
ADC completion ADC on the source of the interrupt being vectored to as shown
Timer 0 overflow TO in Table 16.
1'2 capture 0 em Table 16. Interrupt Vector Addresses
1'2 compare 0 CMO
External interrupt I XI Source Name Vector Address
1'2 capture I CTI
1'2 compare I CMI External interrupt 0 XO 0003H
Timer I overflow TI Timer 0 overflow TO OOOBH
1'2 capture 2 CT2 External interrupt I Xl OOI3H
1'2 compare 2 CM2 Timer I overflow TI OOIBH
SIOO{UART) SO SIOO(UART) SO 0023H
1'2 capture 3 CT3 SIDI (l2C) SI 002BH
Timer 1'2 overflow T2 (lowest) 1'2 capture 0 cro 0033H
The above Priority Within Level structure is only used 1'2 capture I cn 003BH
when there are simultaneous requests of the same prior- 1'2 capture 2 CT2 0043H
ity level. 1'2 capture 3 cn 004BH
ADC completion ADC 0053H
Interrupt Handling 1'2 compare 0 CMO 005BH
1'2 compare I CMl 0063H
The interrupt sources are sampled at S5P2 of every ma- 1'2 compare 2 CM2 006BH
chine cycle. The samples are polled during the following 1'2 overflow 1'2 0073H
machine cycle. If one of the flags was in a set condition
at S5P2 of the previous machine cycle, the polling cycle
will find it and the interrupt system will generate an
LCALL to the appropriate service routine, provided this
hardware generated LCALL is not blocked by any of the
following conditions:
Execution proceeds from the vector address until the
l.An interrupt of higher Or equal priority level is already RET! instruction is encountered. The RETI instruction
in progress. clears the 'priority level active' flip-flop that was set
2. The current machine cycle is not the final cycle in the when this interrupt was acknowledged. It then pops the
execution of the instruction in progress. (no interrupt top two bytes from the stack and reloads the program
request will be serviced until the instruction in counter. Execution of the interrupted program continues
progress is completed). from where it was interrupted.
3. The instruction in progress is RETI or any access to
the interrupt priority or interrupt enable registers. (No 110 PORT STRUCTURE
interrupt will be serviced after RETI or after a read
or write to IPO, IP1, lEO, or lEI until at least one The 83C552 has six 8-bit ports. Each port consists of a
other instruction has been subsequently executed). latch (special function registers PO to P5), an input buff-
er and an output driver (Port 0 to 4 only). Ports 0-3 are
The polling cycle is repeated with every machine cycle, the same as in the 80C51, with the exception of the ad-
and the values polled are the values present at S5P2 of ditional functions of Port l. The parallel I/O function of
the previous machine cycle. Note that if an interrupt flag Port 4 is equal to that of Ports 1, 2 and 3. Port 5 may
is active but is not being responded to because of one of be used as an input port only.
the above conditions, and if the flag is inactive when the
February 1989 2-98

Figure 44 shows the bit latch and liD buffer functional PORT 1 OPERATION
diagrams of the unique 83C552 ports. A bit latch corre-
sponds to one bit in a port's SFR and is represented as Port 1 operates the same as it does in the 8051 with the
a D Type flip-flop. A 'write to latch' signal from the exception of port lines Pl.6 and Pl.7 which may be se-
CPU latches a bit from the internal bus and a 'read lected as the SCL and SDA lines of serial port SI01
latch' signal from the CPU places the Q output of the (I2C). Because the I2C bus may be active while the de-
flip-flop on the internal bus. A 'read pin' signal from vice is disconnected from VDD, these pins are provided
the CPU places the actual port pin level on the internal with open drain drivers. Therefore pins P1.6 and Pl.7 do
bus. Some instructions that read a port read the actual not have internal pull-ups.
port pin levels and other instructions read the latch
(SFR) contents.
READ ALTERNATE
LATCH DUTPUT
READ FUNCTION
LATCH
INTIUS
'NT BUS
WRITETD
LATCH
WA,TE TO
LATCH
READ"N
ALTERNATE
INPUT REAO"N
FUNCTION ALTERNATE
(a) INPUT
FUNCTION
NOlE:
Pull-up not present on P1.6 and P1.7. (b)
'Two period active pull-up as in the 8OC51.
SET FROM
ALTERNATE
READ FUNCTION
LATCH
~
INTIUS P5.X
INT. IUS . PIN
READ"N
WRITE TO
LATCH TOADC
(d)
READ PIN
(c)
Figure 44. Port Bit Latches and 110 Bntrers
February 1989 2-99

PORT 5 OPERATION Table 17. Input/Output Ports
Port 5 may be used to input up to 8 analog signals to the

Port Pin Alternate Function
ADC. Unused ADC inputs may be used to input digital PO.O ADO
inputs. These inputs have an inherent hysteresis to pre- PO. I ADI
vent the input logic from drawing excessive current from PO.2 AD2
the power lines v.hen driven by analog signals. Channel PO.3 AD3 Multiplexed lower order address/data bus
to channel crosstalk (Ct) should be taken into considera- PO.4 AD4 used during external memory"8ccesses
tion when both analog and digital signals are simultane- PO.5 ADS
ously input to Port 5 (see D.C. characteristics in data PO.6 AD6
PO.7 AD7
sheet).
PI.O
Port 5 is not bidirectional and may not be configured as PI.l CTOI } Capture timer input signals for timer T2
Cfn
an output port. All six ports are multifunctional and their PI.2 Cf21
alternate functions are listed in Table 17. A more de- PI.3 Cf31
tailed description of these features can be found in the PI.4 T2 T2 event input
relevant parts of this section. Pl.5 RT2 T2 timer reset signal. Rising edge triggered
Pl.6 SCL Serial port clock line l2C bus
PULSE WIDTH MODULATED OUTPUTS Pl.7 SDA Serial port data line 12C bus
P2.0 AS
The 83C552 contains two pulse width modulated output P2.1 A9
channels (see figure 45). These channels generate puls- P2.2 AIO
es of programmable length and interval. The repetition P2.3 All High order address byte used during
frequency is defined by an 8-bit prescaler PWMP which P2.4 AI2 external memory accesses
supplies the clock for the counter. The prescaler and P2.5 AI3
counter are common to both PWM channels. The 8-bit P2.6 A14
counter counts modulo 255 i.e. from 0 to 254 inclusive. P2.7 AlS
The value of the 8-bit counter is compared to the con- P3.0 RXD Serial input port (UART)
tents of two registers: PWMO and PWMl. Provided the P3.1 TXD Serial output port (UART)
contents of either of these registers is greater than the P3.2 INTO External interrupt 0
counter value, the corresponding PWMO or PWMI output P3.3 INTI External interrupt I
is set LOW. If the contents of these registers are equal P3.4 TO Timer 0 external input
to, or less than the counter value, the output will be P3.S TI Timer I external input
HIGH. The pulse-width-ratio is therefore defined by the P3.6 WR External data memory write strobe
contents of the registers PWMO and PWMI. The pulse- P3.7 RD External data memory read strobe
width-ratio is in the range of 0 to 1 and may be pro- P4.0
grammed in increments of 11255. P4.l CMSROj
CMSRI
P4.2 CMSR2 Timer T2: compare and set/reset outputs
Buffered PWM outputs may be used to drive DC motors. P4.3 CMSR3 on a match with timerT2
The rotation speed of the motor would be proportional to P4.4 CMSR4
the contents of PWMn. The PWM outputs may also be P4.5 CMSR5
configured as a dual DAC. In this application, the PWM P4.6 CMTO } Timer T2: compare and toggle outputs
outputs must be integrated using conventional operational P4.7 CMTI on a match with timer T2
amplifier circuitry. If the resulting output voltages have
PS.O ADCO
to be accurate, external buffers with their own analog
PS.I ADCI
supply should be used to buffer the PWM outputs before
PS.2 ADC2
they are integrated. The repetition frequency fpwm, at PS.3 ADC3 Eight analogue ADC inputs
the PWMn outputs is given by: P5.4 ADC4
PS.S ADC5
fosc PS.6 ADC6
fpwm = --------- PS.7 ADC7
2 x (1 + PWMP) x 255
This gives a repetition frequency range of 92Hz to

23.5kHz (fosc = 12MHz). By loading the PWM registers
with either OOH or FFH, the PWM channels will output
a constant HIGH or LOW level respectively. Since the
8-bit counter counts modulo 255, it can never actually
reach the value of the PWM registers when they are
loaded with FFH.
February 1989 2-100

...z
,.'"....z'"
~
Figure 45. Functional Diagram of Pulse Width Modulated Outputs
When a compare register (PWMO or PWMl) is loaded alog power supplies are connected via separate input
with a new value, the associated output is updated imme- pins. The conversion takes 50 machine cycles i.e. SOIlS
diately. It does not have to wait until the end of the cur- at an oscillator frequency of 12MHz. Input voltage swing
rent counter period. Both PWMn output pins are driven is from OV to + 5V. Because the internal DAC employs
by push-pull drivers. These pins are not used for any a ratiometric potentiometer, there are no discontinuities
other purpose. in the converter characteristic. Figure 46 shows a func-
tional diagram of the analog input circuitry.
Prescaler frequency control register PWMP
Analog-to-Digital Conversion
PWMP(FEH) 171615141312110 Figure 47 shows the elements of a successive approxima-
MSB LSB tion (SA) ADC. The ADC contains a DAC which con-
PWMP.O-7 Prescaler division factor - PWMP + 1. verts the contents of a successive approximation register
to a voltage (VDAC) which is compared to the analog
Reading PWMP gives the current reload value. The ac- input voltage (Vin). The output of the comparator is fed
tual count of the prescaler cannot be read. to the successive approximation control logic which con-
trols the successive approximation register. A conversion
is initiated by setting ADCS in the ADCON register.
PWMO (FCH)
PWMI (FDH) 7I I I I I I
MSB
6 5 4 3 2 1 0
LSB
I ADCS can be set by software only or by either hardware
or software
PWMO/1.0-7} Low/high ratio of PWMn = The software only start mode is selected when control bit
ADCON.5 (ADEX) = O. A conversion is then started by
(PWMn) setting control bit ADCON.3 (ADCS). The hardware or
software start mode is selected when ADCON.5 - 1 and
255 - (PWMn) a conversion may be started by setting ADCON.3 as
above or by applying a rising edge to external pin
ANALOG-TO-DIGITAL CONVERTER
STADC. When a conversion is started by applying a ris-
The analog input circuitry consists of an 8-input analog ing edge, a low level must be applied to STADC for at
multiplexer and a lO-bit, straight binary, successive ap- least one machine cycle followed by a high level for at
proximation ADC. The analog reference voltage and an- least one machine cycle.
February 1989 2-101

, - - - STADC
ADCO +
ADCl
ADC2 ....Iogu. ref.
ADca ANALOGUE INPUT lO-BIT AID
ADC4 MULTIPLEXER CONVERTER
ADC5 IfIIlogua supplV
ADC6
ADC7 analogue ground
ADCON ADCH
INTERNAL BUS
Figure 46. Functional Diagram of Analog Input Circuitry
The low-to-high transition of STADC is recognized at

the end of a machine cycle and the conversion com-
COMPARATOR
mences at the beginning of the next cycle. When a con-
version is initiated by software, the conversion starts at
the beginning of the machine cycle which follows the in-
struction that sets ADCS. ADCS is actually implemented
with two flip-flops: a command flip-flop which is affected
by set operations, and a status flag which is accessed
SUCCESSIVE SUCCESSIVE during read operations.
APPROXIMATION APPROXIMATION
REGISTER CONTROL
LOGIC The next two machine cycles are used to initiate the
converter. At the end of the first cycle, the ADCS status
flag is set and a value of '1' will be returned if the
ADCS flag is read while the conversion is in progress.
START STOP
Sampling of the analog input commences at the end of
the second cycle.
FULL SCALE 1 15/16 58/64
V;n ------~~-i...._-~----- During the next eight machine cycles, the voltage at the
3/4 7/8 28/32
.....;;.;...;.. previously selected pin of Port 5 is sampled and this in-
put voltage should be stable in order to obtain a useful
sample. In any event, the input voltage slew rate must be
less than lOY/ms in order to prevent an undefined result.
The successive approximation control logic first sets the

most significant bit and clears all other bits in the suc-
cessive approximation register (10 0000 OOOOB). The
output of the DAC (50% full scale) is compared to the
input voltage Yin. If the input voltage is greater than
VDAC, then the bit remains set; otherwise it is cleared.
Figure 47. Successive Approximation ADC
February 1989 2-102

TIle successive approximation control logic now sets the

next most significant bit (11 0000 OOOOB or 01 0000
OOOOB depending on the previous result) and VDAC is
compared to Yin again. If the input voltage is greater
than VDAC, then the bit being tested remains set; oth- Start of Conversion
erwise the bit being tested is cleared. This process is
repeated until all ten bits have been tested at which
stage the result of the conversion is held in the succes-
sive approximation register. Figure 48 shows a conver-
sion flow chart. The bit pointer identifies the bit under
test. The conversion takes four machine cycles per bit.
The end of the lO-bit conversion is flagged by control bit

ADCON.4 (ADCI). The upper 8 bits of the result are
held in special function register ADCH and the two re-
maining bits are held in ADCON.7 (ADC.l) and
ADCON.6 (ADC.O). The user may ignore the two least
significant bits in ADCON and use the ADC as an 8-bit
converter (8 upper bits in ADCH). In any event, the to-
tal actual conversion time is 50 machine cycles. ADCI
will be set and the ADCS status flag will be reset 50 cy-
cles after the command flip-flop (ADCS) is set.
Control bits ADCON.O, ADCON.l and AD CON. 2 are

used to control an analog multiplexer which selects one
of eight analog channels (see Figure 49). An ADC con-
version in progress is unaffected by an external or soft-
ware ADC start. The result of a completed conversion
remains unaffected provided ADCI = logic 1. While
ADCS = logic 1 or ADCI = logic 1, a new ADC
START will be blocked and consequently lost. An ADC
conversion already in progress is aborted when the Idle
or Power-down mode is entered. The result of a com-
pleted conversion (ADCI = logic 1) remains unaffected
\\hen entering the Idle mode.
ADC Resolution and Analog Supply
Figure 50 shows how the ADC is realized. The ADC has

its own supply pins (AVDD and AVss) and two pins
(Vref+ and Vref-) connected to each end of the DAC's
resistance-ladder. The ladder has 1023 equally spaced
taps, separated by a resistance of 'R'. The first tap is
located 0.5 x R above Vref- and the last tap is located
1.5 x R below Vref+. This gives a total ladder resistance
of 1024 x R. This structure ensures that the DAC is
monotonic and results in a symmetrical quantization er-
ror as shown in Figure 51.
For input voltages between Vref- and (Vref-) + 112

LSB, the lO-bit result of an AlD conversion will be 00
0000 OOOOB = OOOH. For input voltages between (Vref+)
- 3/2 LSB and Vref+, the result of a conversion will be End of Conversion
11 1111 l111B = 3FFH. AVref+ and AVref- may be be-
tween AVDD + 0.2V and AVss- 0.2V. AVref+ should be
positive with respect to A Vref- and the input voltage
(Vin) should be between AVref+ and AVref-. If the ana- Figure 48. AID Conversion Flowchart
log input voltage range is from 2V to 4V, then ten bit
resolution can be obtained over this range if AVref+ =
4V and AVref- = 2V.
February 1989 2-103

7 6 5 4 3 2 I 0
ADCON(CSH) IADC.I I ADC.O I ADEX I ADCI I ADCS I AADR21 AADR) AADRO I I

Bit Symbol Function
ADCON.7 ADC.I Bit I of ADC result

ADCON.6 ADC.O Bit 0 of ADC result
ADCON.S ADEX Enable external start of conversion by ST ADC
0= Conversion can be started by software only (by sening ADCS)
I = Conversion can be started by software or externally
(by a rising edge on STADC)
ADCON.4 ADCI ADC interrupt flag: this flag is set when an NO conversion result is
ready to be read. An interrupt is invoked if it is enabled.
The flag may be cleared by the interupt service routine. While this
flag is set, the ADC can not start a new conversion. ADCI can not be set
by software.
ADCON.3 ADCS ADC start and status: setting this bit starts an NO conversion. It may
be set by software or by the external signal STADC. The ADC logic
ensures that this signal is HIGH while the ADC is busy. On completion
of the conversion, ADCS is reset at the same time the interrupt flag
is set. ADCS can not be reset by software. A new conversion may not
be started while either ADCS or ADCI is high.
ADCI ADCS ADC Status
0 0 ADC not busy, a conversion can be started

0 I ADC busy, start of a new conversion is blocked
I 0 Conversion completed, start of a new conversion
is blocked
I I Not possible
ADCON.2 AADR2 Analogue input select: this binary coded address selects
ADCON.I AADRI one of the eight analogue port bits of PS to be input to
ADCON.O AADRO the converter. It can only be changed when ADCI and ADCS
are both LOW.
AADR2 AADRI AADRO Selected Analogue Channel
0 0 0 ADCO(PS.O)
0 0 I ADCI (PS.l)
0 I 0 ADC2(PS.2)
0 I I ADC3 (PS.3)
I 0 0 ADC4 (P5.4)
I 0 I ADC5(PS.S)
I I 0 ADC6(PS.6)
I I 1 ADC7 (PS.7)
Figure 49, ADC Control Register (ADCON)
February 1989 2-104

R/2
I.
MSB
1023
R
R start
1022
R
1021
SUCCESSIVE
tota I resistance SUCCESSIVE
APPROXIMATION
= 1023 R + 2 x R/2 DECODER APPROXIMATION
CONTROL
= 1024 R REGISTER
LOGIC
,-- - 3
2
ready
R
R
o LSB
R/2
value 0000 0000 00isoutputforvoltagesVref_toIVref_+l/2 LSB)

value 1111 1111 11 is output for voltages IVref+ _3/ 2 LSB) to Vref+
Figure 50. ADC Realization
The result can always be calculated from the following Timer 1

formula: Timer T3
SIOO SI01
Yin - AVref- External interrupts
Result ~ 1024 x - - - - - - -
AVref+ - A Vref- When the 83C552 enters the Power-down mode, the os-
cillator is stopped. The Power-down mode is entered by
POWER REDUCTION MODES setting the PD bit in the PCON register. The PD bit can
only be set if the EW input is tied HIGH.
The 83C552 has two reduced power modes of operation:
the Idle mode and the Power-down mode. These modes Power·Down Mode
are entered by setting bits in the PCON special function
register. When the 83C552 enters the Idle mode, the fol- The instruction that sets PCON.1 will be the last instruc-
lowing functions are disabled: tion executed in the normal operating mode before the
Power-down mode is entered. In the Power-down mode,
CPU (halted) the on-chip oscillator is stopped. This freezes all func-
Timer T2 (halted and reset) tions; only the on-chip RAM and special function regis-
PWMO,PWM1 (reset; outputs are high) ters are held. The port pins output the contents of their
ADC (conversion aborted if in progress) respective special function registers. A hardware reset is
the only way to terminate the Power-down mode. Reset
In Idle mode, the following functions remain active: re-defines all the special function registers, but does not
Timer 0 change the on-chip RAM.
February 1989 2-105

code
101
out
[7
I 100
/
V
/
all
V
010 /
V
001 /
V
000 /
a q 2q 3q 4q 5q
Quantization Error - V in
q = LSB =5 mV
lTV lTV V
-q/2 -Vin
Symmetrical Quantization Error
Figure 51. Effective Conversion Characteristic
In the Power-down mode, VDD and AVDD can be re- Power Control Register PCON
duced to minimize power consumption. VDD and AVDD
must not be reduced before the Power-down mode is en- The Idle and Power-down modes are entered by writing
tered and must be restored to the normal operating volt- to bits in PCON. PCON is not bit addressable. See Fig-
age before the Power-down mode is terminated. The re- ure 52.
set that terminates the Power-down mode also freezes
the oscillator. The reset should not be activated before MEMORY ORGANIZATION
VDD and AVDD are restored to their normal operating
level, and must be held active long enough to allow the The memory organization of the 83C552 is the same as
oscillator to restart and stabilize (normally less than in the 80C51, with the exception that the 83C552 has 8K
10ms). ROM, 256 bytes RAM and additional SFR's. Addressing
modes are the same in the 83C552 and the 80C5!. De-
The status of the external pins during' Power-down is tails of the differences are given in the following
shown in Table 18. If the Power-down mode is entered par agr a phs.
while the 83C552 is executing out of external program
memory, the port data that is held in the P2 special In the 83C552, the lower 8K of the 64K program mem-
function register is restored to Port 2. If a port latch ory address space is filled by internal ROM. By tying the
contains a '1', the port pin is held HIGH during the EA pin high, the processor fetches instructions from in-
Power-down mode by the strong pull-up transistor.
February 1989 2-106

mode memory ALE PSEN Port 0 Port 1 Port 2 Port 3 Port 4 PWMO/PWMl
Idle (1) internal 1 port data port data port data port data port data HIGH
Idle (1) external 1 1 floating port data address port data port data HIGH
Power-down internal 0 0 port data port data port data port data port data HIGH
Power-down external 0 0 floating port data port data port data port data HIGH
Certain locations in program memory are reserved for

specific programs. Locations OOOOH to 0002H are re-
served for the initialization program. Following reset, the
CPU always begins execution at locations OOOOH. Loca-
6 o tions 0OO3H to 0075H are reserved for the fifteen inter-
rupt request service routines.
PCON (87H) LIs_M_o_DJ.I_-l__J.I_WL_E,lI_G_F'....1.I_G_FO.....lI_PD_LI_lDL-...II
Functionally, the internal data memory is the most flex-
ible of the address spaces. The internal data memory
Bit Symbol Function space is subdivided into a 256-byte internal data RAM
address space and a 128-byte special function register
PCON.7 SMOO Double Baud rate bit. When set to logic I (SFR) address space, as shown in Figure 53.
the baud rate is doubled when the serial port
SIOO is being used in Modes 1.2 or 3.
PCON.6 (reserved)
PCON.5 (reserved)
PCONA WLE Watchdog load enable. This flag must be set
by software prior to loading Timer T3
(watchdog timer). It is cleared when Timer OVERlAPPED
T3 is loaded. ~ ."Cf
PCON.3 GFI General-purpose flag bit ffi r----,' m
PCON.2 GFO General-purpose flag bit
PCON.I PO Power-down bit. Setting this bit activates the
Power-down mode. It can only be set if input
EWishigh.
INDIRECT
ADDRESSING
......
128 BYTES
SPECIAl
FUNCTION
DIRECT
INTERNAL ADDRESSING
PCON.O IDL Idle mode bit. Setting this bit activates the ONLY
.AM
REGISTEftS ONLY
Idle mode.
If logic Is are written to PD and IDL at the same time, PD

takes precedence. The reset value of PCON is (OXXOOOOO).
12 7
!!
ADORESSABlE { 127 12.
IITS IN RAM
Figure 52. Power Control Register (pCON) 112BSITSI 32 7
.7
• DIRECTOR
INDIRECT
lANK 3
ternal program ROM. Bus expansion for accessing pro-

•• .7
BANK 2
ADDRESSING
REGISTERS 1! ••
gram memory from 8K upwards is automatic since ex- .7
ternal instruction fetches occur automatically when the .!. ••

.7
BANK 1
program counter exceeds 8191. If the EA pin is tied low •• BANKO
all program memory fetches are from external memory.

The execution speed of the 83C552 is the same regard- INTERNAL
DATA RAM
less of whether fetches are from external or internal
program memory. If all storage is on-chip, then byte lo-
cation 8191 should be left vacant to prevent an undesired
pre-fetch from external program memory address 8192.
Figure 53. Internal Data Memory Address Space
February 1989 2-107

The internal data RAM address space is 0 to 255. Four The SFR address space is 128 to 255. All registers ex-
8-bit register banks occupy locations 0 to 31. 128 bit lo- cept the program counter and the four 8-bit register
cations of the internal data RAM are accessible through banks reside in this address space. Memory mapping the
direct addressing. These bits reside in 16 bytes of inter- SFRs allows them to be accessed as easily as internal
nal data RAM at locations 20H to 2FH. The stack can RAM and as such, they can be operated on by most in-
be located anywhere in the internal data RAM address structions. The 56 SFRs are listed in Figure 54 and their
space by loading the 8-bit stack pointer. The stack depth mapping in the SFR address space is shown in Figures
may be 256 bytes maximum. 55 and 56. RAM bit addresses are the same as in the
80C51 and are summarized in Figure 57. The special
function bit addresses are summarized in Figure 58.
ARITHMETIC REGISTERS: TIMERS:

ACCumulator"', B register*, Timer MODe, Tuner CONtrol*,
Program Status Word* Timer Low 0, Timer High 0,
Timer Low I, Tuner High I,
POINTERS: TiMer T2 CONtrol, TiMer Low 2,
Stack Pointer, Timer High 2, Timer T3
Data Pointer (High and Low)
CAPTURE AND COMPARE LOGIC
PARAlLEL 110 PORTS: CapTure CONtrol,
Pon 5*, Pon 4*, Pon 3*, TiMer T2 Interrupt flag Register,
Pon 2* ,Port 1*, Pon 0* CapTure Low 0, CapTure High 0,
CapTure Low I, CapTure High I,
INTERRUPT SYSTEM: CapTure Low 2, CapTure High 2,
Interrupt Priority 0* , CapTure Low 3, CapTure High 3,
Interrupt Priority 1*, CoMpare Low 0, CoMpare High 0,
Interrupt Enable 0*, CoMpare Low I, CoMpare High I,
Interrupt Enable 1* CoMpare Low 2, CoMpare High 2
SeT Enable, ReseT Enable
PULSE WIDTH MODULATED OIP's
Pulse Width Modutation Prescaler ADC
Pulse Width Modulation Register 0, ADC cONtrol, ADC High byte
Pulse Width Modulation Register I
SERIAL 110 PORTS:

Serial 0 CONtrol*, Serial 0 data BUFfer,
Serial I CONtrol*, Serial 1 DATa,
Serial 1 STAtus, Serial 1 ADDress, PeON
Note: * Bit and byte addressable
Figure 54. Special Function Registers
February 1989 2-108

REGISTER DIRECT REGISTER DIRECT

MNEMONIC BIT ADDRESS BYTE ADDRESS (HEX) MNEMONIC BIT ADDRESS BYTE ADDRESS (HEX)
i
~rl-----------J~--------~,rA. ~, ,r-"'--,
I I
I I
*
:::
T31
PWMO _
FFH
:~:
_ FCH
IPO I 8F I 8E I BO 18c I 881 8A 1 88 188 I88H -
~
P3 87 j 88 j 85/ 84/ B3/ B2 / B, /80 BOH_

'"'IFF I FE I FO I FC I F81 FA I F81 F8IF8H- it CTL3
• CTL2
AFH
AEH
F71 F6 1 F5 1 F4/ F3/ F2/ " / FO FOH_ # eTL 1 AOH
It CTLO ACH
RTE f------------------------1 EFH
STE EEH CML2 AIIH
'ltTMH2 EOH eMU AAH
.. TML2 ECH CMLO A8H
CTeON EBH IENO AFjAEjAOjACjAB/AA/A9/A8 ABH-
TM2CON
lEN' I EF I EE I EO I EC I EB.I fA I E9 I E8 I
EAH
E6H -
P2 I
't.
A7 I A6 I A51 A41 A31 A21 ", I AO I AOH -
ACC I E7 I E6 I E5 I E4 I E3 I E2 IE, I EO I EOH -

SOBUF
SOCON r :9:F:'l'lr.9::ET:/9::0"-:
/87c T:"
19":"aT:"" 19:":9:-'Ir a--1a
18A:-,r
aSH
8aH-
1
SFAs containing
0:::= ~ directly edd,....ble
bits
~~R ~H P' 9 7 1 86 185184 183 18218, 1901 80H -
SFRs containing
SWAT f----------------J OAH directly IKkIreaable
bits
.. 51STA 09H THl 80H
THO r-----------------J
S,CON OF / DE I 00 I DC I oa I OA 109/ 08 oaH- 8CH
TL1 8B H
PSW 07 Ille 105 /04 / 03/ 02/ 0' /00 OOH_ TLO 8AH
* CTH3 CfH TMOO 89H
II CTH2 CEH TCON 8F 18E I 80 I 8C 1 8B laA I a9.188 BeH-
#~, COH peON 87H
#CTHO CCH
r-----------------~
CMH2 CBH DPH 83H
CMHl CAH DPl 82H
CMHO C9H SP 81 H
TM21R CF / CE / CO / cc I C8 I CA I CB I C8 C8H- PO 87 I 86 I 85 I 84j83J 82J 8' / BO 80H_
"""1p.l
ADeON
# P5
c71 col C51 c41 C3 I c21 c, I co

1mT C6H
C4H
COH -
I I
I I
Figure 55. Mapping of Special Function Registers
February 1989 2-109

Signetics Microprocessor Products User's Guide.
SPECIAL
FUNCTION
REGISTERS
r----"--...,
-255
241
240
232
224
216
201
255 244
-@
FOH
EIH
Eok
OIH
DOH
200 CIM
DIRECT
112 COH
ADDIIESS-
II. IIH ING
176 BOH (BITSI
lSI AIM
110 AOH
:3
152 IIH
144
136
127 -
128 135 121
41
DIRECT 127 120
ADDRESSING
(BITSI
.E. 7 0
A7
BANK 3
~ AO
R7 BANK 2
REGISTER .!! AO
ADDRESSING A7
BANK 1
I AO
R7
BANKO
0 RO
'----;---y-----
~ DIRECT ADDRESSING
STACK·PDINTER REGISTER·INDIRECT AND
REGISTER.INDIRECT ADDRESSING
Figure 56. Special Function Register Bit Address
February 1989 2-110

!'
DIRECT BYTE REGISTER

ADDRESS (HEXI BIT ADDRESS MNEMONIC
,.--A----.. ,,-_ _ _ _- J ._ _ _ _---., ~
.... ,. .. PT2 PeM2 PeMl PeMO PeT3 PCT2 PeT1 PCTO
...." ... ...••

7F 70 70 7C 7A 71 FB H FF I FE I FD I FC I FB I FA I Fe I FB IPI
,.
OEH
2DH
77
IF
., •
.. . . . ..
71
10
7.
Ie
73 72
IA
70
Fa H F7 I F6 I F5 I FO I F3 I F2 I Fl I FO
2CH
2BH SF
.,
51 50 5C . ..
13
SA
., ..••
51 51
E8H
ET2 ECM2 ECMl ECMO ECT3 Ecn ECn ECTO
EF I EE I ED I EC I EB I oA I E9 I EB IEN1
-- . ..... . ..•• .. .. .. .,
OAH 51 55 51 53 so EOH E7 I E6 I E5 I E4 I E3 I E2 lEI I EO ACC
., .. . -
'F 4E IC .A
ENSI STA STO SI AA CRI CRO
'7
.. .. .. D8H OF I DE I DO I DC I 08 I DA I 09 I 08 SICON
- .
, 7H .F 3E 3D 3C SA CV AC FO RSI RSO OV Fl P
DOH I I I I I I 01 I DO PSW
.. ....
07 08 05 04 03 02
37 :II os 53 53 31 3D :II
T20V CMI2 CMII CMIO CTI3 eTt2 CTII CTIO
,OH
.F
27 ..,. .. .. ,. .
2E 2D 2C I 2B
23
,A
"
37
:II
C8H CF I CE I CD I CC I CB I CA I C9 I C8 TM2IR
... ..,. ..,. . " ... ..

,3H IF 10 lA 11 35 I C6 I C5 I C4 j I I I CO
11
lC
"
n 10
COH C7
-
C3 C2 Cl P4
" "
I
PAD PSI PSO PTI
I BD I BC I BI I BA I B9 I BB
PXl PTO PXO
-
21H OF 00 oc OA Of 33 B8H 8F 8E IPO
07 GO O' 01 32
l FH
..... 31
••
BOH B7
EA
I B6
EAD
I 85
ESI
I
I
B4
ESO
I B3 I
ETI
B2
EXI
I AI I AA I A9 I A8
I Bl I BO
ETO EXO
P3
''''
.....
A8H AF 1 AE-l AD AC lEND
17H .3
IOH 1
AOH A 71 A6l AS I A4 I A3 I A2 I A 1 I AD P2
--
OFH 1 SMO SMl 5M2 REN Tea R8B TI RI
'Mlk 1 98H 9F 1 9E1 90 I 9C I 98 I 9A I 99 I 98 SOCON
07H
..... 0 90H 97 I 96 I 95 94 I 93 I 92 I 91 I 90 PI
TFI TR' TFO TRO lEI ITI lEO ITO

88H 8F I 8E I 80 BC I 81 I SA I 89 I 88 TCON
BaH 87 I 86 I 85 84 I 83 I 82 I 81 I 80 PO
Figure 57. RAM Bit Addresses Figure 58. Special Function Register Bit Address
February 1989 2-111

Signefics S83C552/S80C552
With AID, Capture/Compare Timer,
With High-Speed Outputs, PWM

The S83C552/S80C552 Single-Ghip 8-Bit • SC80C51 B central processing
Microcontroller is manufactured in an ad- unit
Goo
vanced CMOS process and is a deriva- • 8K x 8 ROM (83C552), expand- INDEX
CORNER 9 1 61
tive of the SC80C51 microcontroller fam- able externally to 64K bytes
ily. The S83C552/S80C552 has the same .256 x 8 RAM, expandable
instruction set as the 80C51. Two ver- externally to 64K bytes
sions of the derivative exist: • Two standard 16-bit timer! PLCC
counters
o S83C552 - 8K bytes mask program- • An additional 16-bit timer! 26 44
mable ROM counter coupled to four
o S80C552 - ROMless version of the 27 43
capture registers and three
S83C552 compare registers TOP VIEW
• Capable of producing 8 synch- Pin Function Pin Function
The S83C552 contains a non-volatile 8K
ronized, timed outputs 1 P5.0/ADCO 35 XTALI
x 8 read-<lnly program memory, a volatile 2 VDD 36 Vss
• A 10-bit ADC with 8 multi-
256 x 8 read/write data memory, six 8- 3 STADC 37 Vss
plexed analog inputs 4 PWMO 38 NC
bit I/O ports, two 16-bit timer/event
• Two 8-bit resolution, pulse 5 PWMI 39 P2.0/A08
counters (identical to the timers of the
width modulation outputs 6 EW 40 P2.1/A09
SC80C51), an additional 16-bit timer 7 P4.0/CMSRO 41 P2.2/Al0
• Five 8-bit I/O ports plus one
coupled to capture and compare latches, 8 P4.1/CMSRI 42 P2.3/All
8-bit input port shared with 9 P4.2/CMSR2 43 P2.4/AI2
a 15-source, two-priority-Ievel, nested in-
analog inputs 10 P4.3/CMSR3 44 P2.5/A13
terrupt structure, an 8-input ADC, a dual
• 12C-bus serial I/O port with byte 11 P4.4/CMSR4 45 P2.6/A14
DAC pulse width modulated interface, 12 P4.5/CMSR5 46 P2.7/A15
oriented master and slave
two serial interfaces (UART and 12C-bus), functions
13 P4.6/CMTO 47 PSEN
a 'watchdog' timer and on-chip oscillator 14 P4.7/CMTI 48 ALE
• Full-duplex UART compatible 15 RST 49 EA
and timing circuits. For systems that re- with the standard 80C51 16 P1.0/CTOI 50 POJ/AD7
quire extra capability, the S83C552 can • On-chip watchdog timer 17 P1.1/CT11 51 PO.6/AD6
be expanded using standard TTL compat- 18 P1.2/CT21 52 PO.5/AD5
ible memories and logic. 19 P1.3/CT31 53 PO.4/AD4
20 P1.4/T2 54 PO.3/AD3
LOGIC SYMBOL 21 P1.5/RT2 55 PO.2/AD2
The device also functions as an arith- 22 P1.6/SCL 56 PO.1/AD1
metic processor having facilities for both 23 P1.7/SDA 57 PO.O/ADO
binary and BCD arithmetic plus bit-hand- 24 P3.0/RXD 58 AVref-
I-I-
ling capabilities. The instruction set con- 25 P3.1/TXD 59 AVref+
0::: LOW ORDER 26 P3.2/INTO 60 AVSS
sists of over 100 instructions: 49 one- EA ~_ A~ESS
27
I5l!m P3.3/1NT1 61 AVDD
byte, 45 two-byte and 17 three-byte. ALE ::: DATA BUS 28 P3.4/TO 62 P5.7/ADC7
With a 12MHz crystal, 58% of the in- AVss 29 P3.5/T1 63 P5.6/ADC6
AVCO 30 P3.6/WR 64 P5.5/ADC5
structions are executed in 1!1S and 40%
r~
AVRu+
AVRu- 4-- er11 31 P3.7/RD 65 P5.4/ADC4
in 2!1S. Multiply and divide instructions -+- CT21 32 NC 66 P5.3/ADC3
require 4!1S. ~+-CT31 33 NC 67 P5.2/ADC2
PW5 -rz
--
_RT2 34 XTAL2 68 P5.1/ADC1
--I li::I---
Piiiii _SCI.
ADC1-+ Ill!
ADC2--11o ~
--
ADCl_ ...... ADDRESS
ADC4-__.
AOCS-... - BUS
--( 1--"
ADC8_
ADC7---
CMSR' ....... If)-+TXD/Q..OCK

CIoISR2_
~-JmI
=::~
CN_- ::¥b"
-Tl
CIlIO_ _liR
CNTl_ -III
~
RST
£W
February 1989 2-112 95545

Single-Chip 8-Bit Microcontroller S83C552/S80C552
S8
Cl
1
C552_ClCl ClCl ::r:x: ROM Pattern No.

Signetics. Contact Signetics
sales office for ROM pattern sub-
mission requirements.
Package and Pins
A58 - 58-Pin Plastic PLCC
ROM less Version
S80C552-1 A58
I
I
ROM Version
S83C552-1A58
ITemperature & Package I
I 0 to +70 C plastic PLCC 11.2 to 12MHz
0
Frequency
Speed and Temperature Range

1 - 0 to +70° C. 1.2 to 12MHz
ROMless/ROM
0- ROMless
3 - ROM
BLOCK DIAGRAM
ADCO-7
-+
TO Tl iNTo INTI PiiMii PWiii AVDD STADe SDA SCL
"DD 'Iss
®® ®
,
~
- - - - ;:... ®
- _1- - ~ - - - f..-- - I- - - f..-@L -CD - CD.,
XTALI
, TO. T1
r-''---'
®
XTAL2 TWO 1S-BIT PROGRAM DATA
I SERIAL
TIMER/ CPU MEMORY MEMORY DUAL
ADC
EVENT 8Kx6 258x6 PWM 1'<: PORT
COUNTERS ROM RAM
I
ALE
, :......, 0-
,
8OC51
CORE
EXCLUDING
ROII/RAII
8-BIT
INTERNAL BUS
®'
I
®,
18
J --= '--
A00-7
® , PARALLEL
I/O PORTS
ANO
SERIAL
UART
8-BIT
I/O
PORT
fOUR
III-BIT
CAPTURE
T2
18-BIT
TIMER/
~
TtflEE
til-BIT
COMPARA-
COMPARA-
TOR
OUlPUT
TJ
WATCH-
DOG
PORT EVENT TORS WITH
I EXT BUS LATCHES
COUNTER REGISTERS
SELECTION TIMER
A8-15
®,
L _
-- ® 1®- - - l- I-- 1 - - I-
<D<D
- - - - - -
<D
I-
@
-
- I- - -
PO PI P2 P3 TxD RxD P5 P4 T2 RT2 CMSRG-CMSR5 RST -EW
CIITO. CMTI
@ Alternate fl.nctlon of port 0 @Alternate function of port 3

CD Alternate
function of port 1 @Alternate function of port 4
@Alternate function of port 2 ® Alternate function of port 5
® Not present In 80C552
February 1989 2-113

PIN DESCRIPTION
MNEMONIC PIN NO. TYPE NAME AND FUNCTION
Vee 2 I Digital Power Supply: +5V power supply pin during normal operation, idle and power down
mode.
STADC 3 I Start ADC Operation: Input starting analog to digital conversion (ADC operation can also be
started by software).
PWMO 4 0 Pulse Width Modulation: Output O.
PWM1 5 0 Pulse Width Modulation: Output 1.
EW 6 I Enable Watchdog Timer: Enable for T3 watchdog timer and disable power-down mode.
PO.0-PO.7 57-50 1/0 Port 0: Port 0 is an 8-bit open-drain bidirectional 1/0 port. Port 0 pins that have 1s written to
them float and can be used as high-impedance inputs. Port 0 is also the multiplexed low-order
address and data bus during accesses to external program and data memory. In this application
it uses strong internal pull-ups when emitting 1s.
P1.0-P1.7 16-23 1/0 Port 1: 8-bit 1/0 port. Alternate functions include:
16-21 1/0 (P1.0-P1.5): Quasi-bidirectional port pins.
22-23 1/0 (P1.6, P1.7): Open drain port pins
16-19 I CTOI -CT31 (P1.0-P1.3): Capture timer input signals for timer T2
20 I T2 (P1.4): T2 event input
21 I RT2 (P1.5): T2 timer reset signal. Rising edge triggered
22 1/0 SCL (P1.6): Serial port clock line 12C-bus
23 1/0 SDA (P1.7): Serial port data line 12C-bus
P2.0-P2.7 39-46 1/0 Port 2: 8-bit quasi-bidirectional 1/0 port.
Alternate Function: High-order address byte for external memory (A08-A15).
P3.0-P3.7 24-31 110 Port 3: 8-bit quasi-bidirectional 1/0 port. Alternate functions include:
24 I RxD (P3.0): Serial input port
25 0 TxD (P3.1): Serial output port
26 I INTO (P3.2): External interrupt
27 I INT1 (P3.3): External interrupt
28 I TO (P3.4): Timer 0 external input
29 I !1jP3.5): Timer 1 external input
30 0 WR (P3.6): External data memory write strobe
31 0 RD (P3.7): External data memory read strobe
P4.0-P4.7 7-14 1/0 Port 4: 8-bit quasi-bidirectional 110 port. Alternate Functions include:
7-12 0 CMSRO-CMSR5 (P4.0-P4.5): Timer T2 compare and setlreset outputs on a match with timer T2.
13, 14 0 CMTO, CMT1 (P4.6, P4.7): Timer T2 compare and toggle outputs on a match with timer T2.
P5.0-P5.7 68-62, I Port 5: 8-bit input port.
1 ADCO-ADC7 (P5.0-P5.7): Alternate Function: Eight input channels to ADC.
RST 15 1/0 Reset: Input to reset the S83C552. It also provides a reset pulse as output when timer T3 over-
flows.
XTAL1 35 I Crystal Input 1: Input to the inverting amplifier that forms the OSCillator, and input to the internal
clock generator. Receives the external clock signal when an external oscillator is used.
XTAL2 34 0 Crystal Input 2: Output of the inverting amplifier that forms the oscillator. Left open-circuit when
an external clock is used.
Vss 36, 37 I Digital Ground
PSEN 47 0 Program Store Enable: Active-low read strobe to external program memory.
ALE 48 0 Address Latch Enable: Latches the low byte of the address during accesses to external memory.
It is activated every six oscillator periods. During an external data memory access, one ALE
pulse is skipped. ALE can drive up to eight LS TTL inputs and handles CMOS inputs without an
external pull-up.
EA 49 External Access: When EA is held at TTL level high, the CPU executes out of the internal pro-
gram ROM provided the program counter is less than 8192. When EA is held at TTL low level,
the CPU executes out of external program memory. EA is not allowed to float.
AVREF- 58 Analog to Digital Conversion Reference Resistor: Low-end.
AVREF+ 59 Analog to Digital Conversion Reference Resistor: High-end.
AVss 60 Analog Ground
AVee 61 Analog Power Supply
NOTE.
To avoid 'latch-up' effect at power-on, the voltage on any pin at any time must not be higher or lower than Vee + 0.5V or
VSS - 0.5V respectively.
February 1989 2-114

OSCILLATOR CHARACTERISTICS RESET idle mode is activated. The CPU con-

XTAL1 and XTAL2 are the input and out- A reset is accomplished by holding the tents, the on-chip RAM, and all of the
put, respectively, of an Inverting ampli- RST pin high for at least two machine special function registers remain Intact
as an on-chip oscillator, as shown in the oscillator is running. To insure a good terminated either by any enabled Inter-
logic symbol, page 1. poweroOn reset, the RST pin must be rupt (at which time the process is picked
To drive the device from an external time to start up (normally a few milli- continued), or by a hardware reset
clock source, XTAL1 should be driven seconds) plus two machine cycles. At which starts the processor in the same
while XTAL2 is left unconnected. There poweroOn, the voltage on Vee and RST manner as a poweroOn reset.
input to the internal clock circuitry is In the power-down mode, the oscillator
ever, minimum and maximum high and In the idle mode, the CPU puts itself to power-down is the last instruction exe-
must be observed. stay active. The instruction to inVOke the RAM are preserved. A hardware reset is
Table 1 shows the state of I/O ports


Program PWMOI
Mode ALE PSEN Port 0 Port 1 Port 2 Port 3 Port 4
Memory PWM1
Idle Internal 1 1 Data Data Data Data Data High
Idle External 1 1 Float Data Address Data Data High
Power-down Internal 0 0 Data Data Data Data Data High
Power-down External 0 0 Float Data Data Data Data High
February 1989 2-115

ABSOLUTE MAXIMUM RATlNGS1, 2, 3

Voltage on any other pin to Vss -0.5 to + 6.5 V
1.0 W
NOTES:
noted.
DC ELECTRICAL CHARACTERISTICS TA - O°C to +lO°C, Vee, AVec - 5V ±10%, Vss, AVss - OV
TEST LIMITS
SYMBOL PARAMETER UNIT
CONDITIONS Min Typical1 Max
Vee Supply voltage 4.5 5.5 V
Power supply current:
Active mode @ 12MHz 11.5 30 mA
Icc See note 5
Idle mode @ 12MHz 1.3 7 mA
Power down mode 3 50 /lA
Inputs
Input low voltage, except EA, Pl.6/SCL,
V,L -0.5 0. 2Vee-0. 1 V
P1.7/SDA
V,L1 Input low voltage to EA -0.5 0. 2Vee-0.3 V
V,L2 Input low voltage to P1.6/SCL, P1. 7/SDA6 -0.5 0. 3Vee V

Input high voltage, except XTAL 1, RST,
VIH 0. 2Vee+0.9 Vee+0.5 V
P1.6/SCL, Pl. 7/SDA
VIH1 Input high voltage, XTAL1, RST O.7Vee Vee+0.5 V
VIH2 Input high voltage, P1.6/SCL, Pl.7 ISDA6 0. 7Vee 6.0 V
Logical 0 input current, ports 1, 2, 3, 4, except
-IlL VIN - 0.45V -50 /lA
Pl.6/SCL, Pl, 7/SDA
Logical l-to-O transition current, ports 1, 2, 3,
-ITL See note 4 -650 /lA
4, except P1.6/SCL, Pl.71SDA
±llll Input leakage current, port 0, EA, STADC, EW 0.45V<VI< Vee 10 /lA
OV<VI<6V
±IIL2 Input leakage current, Pl.6/SCL, Pl.71SDA 10 /lA
OV<Vee<5.5V
Outputs
Output low voltage, ports 1, 2, 3, 4 except
VOL IOL - 1.6mA2 0.45 V
Pl.6/SCL, Pl. 7/SDA
Output low voltage, port 0, ALE, PSEN, PWMO,
VOll IOL - 3.2mA2 0.45 V
PWMl
VOL2 Output low voltage, Pl.6/SCL, Pl. 7/SDA IOL - 3.0mA2 0.4 V
-IOH - 60/lA 2.4 V

Output high voltage, ports 1, 2, 3, 4, except Vee - 5V±10% V
VOH Pl.6/SCL, Pl.71SDA V
-IOH - 25/lA 0.75Vee
-IOH - 10/lA 0. 9Vee V
-IOH - 400/lA 2.4 V

Output high voltage (port 0 in external bus Vee - 5V±10% V
VOH1 mode, ALE, PSEN, PWMO, PWM1)3 V
-IOH - 150/lA 0.75Vee
February 1989 2-116

DC ELECTRICAL CHARACTERISTICS (Continued)
TEST LIMITS
CONDITIONS Min Typical 1 Max
Outputs (Continued)
-IOH - 3501lA 2.4
VOH2 High level output voltage (RST) V
-IOH - 601lA 0.75Vcc
RRST Internal reset pulldown resistor 50 150 kQ
Test freq - 1 MHz,
TA - 25°C
Analog Inputs
AVcc Analog supply voltage7 AVcc - Vcc±JJ·2V 4.5 5.5 V
Analog supply current Port 5 - 1.4V
Alcc 1.0 rnA
Operating
AIID 50
AlpD
Idle mode IlA
Power-down AVcc - 2-5.5V 50 IlA
AVIN Analog input voltage AVss-0.2 AVcc+0.2 V
Reference voltage:
V
AVref AVREF- AVss-0.2
AVcc+0.2 V
AVREF+
RREF Resistance between AVREF+ and AVREF- 10 50 kQ
CIA Analog input capacitance 15 pF
tADS Sampling time 8tCY f1S
tADC Conversion time (including sampling time) 50tCY f1S
DLe Differential non-linearity8 -1 +2 LSB
ILe Integral non-linearity8 ±2 LSB
OSe Offset error8 ±10 mV
Ge Gain error8 0.4 %
MCTC Channel to channel matching ±1 LSB
Ct Crosstalk9 0-100kHz -60 dB
NOTES:
to external bus capacitance discharging into the port 0 and port 2 pins when these pins make 1-to-0 transitions during bus operations.
In the worst cases (capacitive loading> 100pF). the noise pulse on the ALE pin may exceed o.av. In such cases, it may be desirable to
qualify ALE with a Schmitt Trigger. or use an address latch with a Schmitt Trigger STROBE input.
3. Capacitive loading on ports 0 and 2 may cause the VOH on ALE and PSEN to momentarily fall below the O.9VCC specification when the
4. Pins of ports 1 (except P1.6, P1.7), 2,3 and 4 source a transition current when they are being externally driven from 1 to O. The transition
current reaches its maximum value when VIN is approximately 2V.
5. See Figures 8 throug h 11 for ICC test conditions.
6. The input threshold voltage of P1.6 and P1.7 (SI01) meets the 12C specification. so an input voltage below 1.5V will be recognized as a log-
ic 0 while an input voltage above 3.0V will be recognized as a logic 1.
7. The following condition must not be exceeded: VCC - 0.2V < AVcc < VCC + 0.2V.
8. Conditions: AVREF- - OV; AVCC - 5.0V. AVREF+ - 5.12V. ADC is monotonic with no missing codes.
9 This should be considered when both analog and digital sig nals are simultaneously input to port 5.
February 1989 2-117

AC ELECTRICAL CHARACTERISTICS TA - O°C to +70°C, VCC. AVcc - 5V ±1 0%. Vss. AVss - OV

Min Max Min Max
Program Memory
l/tCLCL 1 Oscillator frequency 1.2 12 MHz
tLHLL 1 ALE pulse width 127 2tci CI -40 ns
tAVLL 1 Address valid to ALE low 28 tCLCL -55 ns
tLLAX 1 Address hold after ALE low 48 tr.1 C -35 ns
tLLPL 1 ALE low to PSEN low 43 tr.1 r.1 -40 ns
tp IV 1 PSEN low to valid instruction in 145 3tci CI -105 ns
tpxIZ 1 Input instruction float after PSEN 59 tr.lr.I-25 ns
tAVIV 1 Address to valid instruction in 312 5tCLCL-l05 ns
tp.AZ 1 PSEN low to address float 10 10 ns
Data Memory
tAvLL 2, 3 Address valid to ALE low 43 tCLCL -40 ns
tRLRH 2,3 RD pulse width 400 6tCLCL -100 ns
tWLWH 2, 3 WR pulse width 400 6tci cr-1OO ns
tRLDV 2, 3 RD low to valid data in 252 5tCLCL-165 ns
tRHDZ 2, 3 Data float after RD 97 2tCLCL-70 ns
t .DV 2. 3 ALE low to valid data in 517 8tr.1 r.1 -150 ns
tAVDV 2, 3 Address to valid data in 585 9tCLCL -165 ns
t LWL 2. 3 ALE low to RD or WR low 200 300 3tr.1 r.1 -50 3tr.1 r.1 +50 ns
tAVWL 2. 3 Address valid to WR low or RD low 203 4tCLCL -130 ns
tOVWX 2. 3 Data valid to WR transition 23 "'" r.1 -60 ns
tWHOX 2, 3 Data hold after WR 33 tCLCL -50 ns
tRiAZ 2. 3 RD low to address float 12 12 ns
tWHLH 2, 3 RD or WR high to ALE high 43 123 tCLCL -40 tCLCL+40 ns
External Clock
tCHCX 5 High time 3 20 20 ns
tCLCX 5 Low time 3 20 20 ns
tCLCH 5 Rise time3 20 20 ns
tCHCL 5 Fall time 3 20 20 ns
Shift Register
tXLXL 4 Serial port clock cycle time 3 1.0 12tCLCL fLS
tOVXH 4 Output data setup to clock rising edge 3 700 1OtCLCL-133 ns
tXHQX 4 Output data hold after clock rising edge 3 50 2tCLCL -117 ns
tXHDX 4 Input data hold after clock rising edge 3 0 0 ns
tXHDV 4 Clock rising edge to input data valid 3 700 1OtCLCL -133 ns
NOTES:
2. Load capacitance for port 0, ALE, and PSEN - 100pF. load capacitance for all other outputs - 80pF.
3. These values are characterized but not 100% production tested.
February 1989 2-118

Single-Chip 8-Sit Microcontroller S83C552/S80C552

Each timing symbol has five characters. The first character is P- PSEN
always 't' (- time). The other characters, depending on their Q - Output data
positions, indicate the name of a signal or the logical status of R - RD signal
that signal. The designations are: t - Time
A - Address V - Valid
C - Clock W - WR signal
o - I nput data X - No longer a valid logic level
H - Logic level high Z - Float
I - Instruction (program memory contents) Examples: tAVLL - Time for address valid to ALE low.
L - Logic level low, or ALE tLLPL - Time for ALE low to PSEN low.
ALE
PORTO
PORT 2 _ _ _ _oJ'
ALE
PORTO IN
PORT 2 _ _ _./ I'-------------------J

February 1989 2-119

ALE
--~~-----IWlWH'------~
'OVWX
PORTO DATA OUT AD-A? FROM PCl
ALE
'OVXH HI 'XHOX
OUTPUT DATA
\'--_~ '-_~ '--_~ '-_---' '--_..J ' - _ - - I '--_..J '-_--.J
f
WRITE TO SBUF
I INPUT DATAl _ _ _ _ _ _ _J
f t
CLEAR RI
SET RI
February 1989 2-120

O.45V
~---------tCLCL--------~
Vcc-O.5
0.45V
=x O.2Vcc+O.9
_,-O",.",2V.;.,c",c,--..;.O",.1_ __
>C Timing
Reference
Points

for a logic "1" and 0.45V for a logic '0".
the 10adedVoHIVOL level occurs.IOH/lOL~±20mA.

40
MAX ACTIVE MODE
35
/
30 V
25
/
f V
~ 20
()
Q
15 / TYP ACTIVE MODE
/ ./
V
10
5
I
VV V MAX IDLE MODE
:::::::. ~ I---I - -
TYP IDLE MODE
FREQ AT XTAL1

Valid only within frequency specifications of the device under test.
Maximum values taken at Vcc = 5.5V and worst case temperature.
Typical Values taken at Vcc = 5.0V and 25°C.
February 1989 2-121

Vee Vee
...-_ _ _ _-;Iee
Vee
!
Vee
Vee
RST
RST
(NC) XTAL2 XTAL2

CLOCK (NC) XTAL1
CLOCK XTALI

0.45V
~--------tCLCL----------~
tCLCH =
tCHCL =
5ns
Vee
...-_ _ _ _-;Iee
Vee
1
Vee
RST
(NC) XTAL2
XTAL1
Vss

February 1989 2-122

8XC652 OVERVIEW The organization of the data memory is similar to the

80C51 except that the SXC652 has an additional 128
The SXC652 is a derivative of the 80C51 8-bit CMOS bytes of RAM overlapped with the special function regis- i-
microcontroller. The 8XC652 contains all of the features ter space. This additional RAM is addressed using indi-
of the 80C51 (that is the standard counter/timers TO and rect addressing only and is available as stack space.
Tl, the standard serial I/O (UART) , and four 8-bit 110 (This memory addition is the same as in the S052 and
ports). In addition, the 8XC652 has the following: 83C552. See Figure 59 for a memory map.)
Special Function Registers

• 8K bytes of ROM
• 256 bytes of RAM
The 8XC6S2 special function register space is the same
• I2C bus serial 110
as that on the 80C5l except that it contains four addi-
The 8XC652 is pin-for-pin compatible and fully code tional SFRs. The added registers are: SlCON, S1STA,
compatible with the SOC5l. There are some differences S1DAT, and SlADR. In addition to these the standard
in the Pl.6 and Pl.7 pin functions that are described in UART special function registers, SCaN and SBUF have
detail" later in this section. All of the 80C5l functions been renamed SOCON and SOBUF for clarity.
are present including the external 64K program and data
memory expansion, Boolean processing, and two reduced Since the standard 80CSl on-chip functions are the same
power modes. on the 8XC652, the SFR locations, bit locations, and op-
eration are unchanged. The only exception is in the in-
Differences from the 80C51 terrupt enable and interrupt priority SFRs. These have
been changed to include the interrupt from the I2C se-
The data and program memory are organized similar to rial port. Table 19 shows the special function registers,
the SOC51. The 8XC652 program memory differs in that their direct address, the bit addresses, and the value in
it has 8K bytes of on-chip ROM. When EA is high the the register after a reset.
8XC652 fetches instructions from the internal ROM un-
less the address exceeds 1FFFH. Locations 2000H to
FFFFH~re fetched from external program memory.
When EA is held low, all instruction fetches are from
external memory.
64K
64K .....- - - - ,
EXTERNAL
8192
t
819 1
r 8191
1
INTERNAL EXTERNAL 255 r----..::.,

lEA-II IEA-OI
127 ------
INTERNAL
0
o DATA RAM
0'------'
y '---v-----'
PROGRAM MEMORY INTERNAL EXTERNAL
DATA MEMORY DATA
MEMORY
FIgure 59. Memory Map
February 1989 2-123


Symbol Description Address MSB Reset Value
LSB
ACC· Accumulator EOH E7 E6 ES E4 E3 E2 El EO OOH
B' B register FOH F7 F6 FS F4 F3 F2 Fl FO OOH
IE' Interrupt enable A8H EAl I ESI IESO I ETl I EXI I ETO I ETl OXOOOOOOB
Ip· Interrupt priority B8H - I I PSI I PSO I PTl I PXl I PTO I PXO xxOOOOOOB
87 86 85 84 83 82 81 80
PO' Port 0 80H AD7 I AD6 I ADS I AD4 I AD3 I AD2 I ADI I ADO FFH
97 96 95 94 93 92 91 90
PI • Port 1 90H SDAj SCL I I I I I I FFH
A7 A6 AS A4 A3 A2 Al AO
P2' Port 2 AOH AlSj A14 I A13 I A12 I All I AlO I A9 I A8 FFH
B7 B6 BS B4 B3 B2 Bl BO
P3' Port 3 BOH RD I WR I Tl I TO I INTlI INTO I TXD I RXD FFH
PCON Power control 87H SMODl - I - I - I GFI I GFOI PD I IDL OxxxOOOOB
9F 9E 9D 9C 9B 9A 99 98
SOCON*# Serial 0 port control 98H SMO I SMI I SM2 I REN I TBB I RBB I TI I RI OOH
SOBUF# Serial 0 data buffer 99H xxxxxxxxB
D7 D6 DS D4 D3 D2 Dl DO
PSW' Program status word DOH CY J AC I FO I RSI I RSO I OV I FI I P OOH
SlDAT# Serial 1 data DAH OOH
SIADR# Serial 1 address DBH SLAVE ADDRESS I GC OOH
SISTA# Serial 1 status D9H SC4l SC3 I SC2 I SCI I SCO I 0 I 0 I 0 F8H
SICON*# Serial 1 control D8H - lENSll STA I STO I SI I AA I CRI I CRO xOOOOOOOB
8F 8E 8D 8C 8B 8A 89 88
TCON* Timer control 88H TFI I TRI I TFO I TRO I IEl I ITl I IEO I ITO OOH
THI Timer high 1 8DH OOH
TLl Timer low 1 8BH OOH
TMOD Timer mode 89H GATEJ CIT I Ml I MO IGATE I CIT I Ml I MO OOH
* = SFRs are bit addressable
# = SFRs are modified from or added to the 80CSI SFRs.
I2C Serial Communication - SIOI and timer blocks to continue to function while the CPU
is halted. The following functions remain active during
The I2C Serial port is identical to the I2C serial port on idle mode. These functions may generate an interrupt or
the 83C552. The operation of this subsystem is described reset and thus end the idle mode:
in detail in the 83C5S2 section of this manual.
- Timer O. Timer 1
Note that in both the 8XC6S2 and the 83CS52 the I2C - SIoO. SIOl
pins are alternate functions to port pins PI.6 and PI.7. - External interrupt
Because of this PI.6 and PI. 7 on these parts do not have
a pull-up structure as found on the 80CSI. Therefore In idle mode. port pins PI.6 and PI.7 function as SCL
PI.6 and PI.7 have open drain outputs on the 8XC652. and SDA respectively if the I2C serial port is enabled.
The power-down operation freezes the oscillator. TIle
Idle and Power-down Operation power-down mode can only be activated by setting the
PD bit in the PCON register. The power-down mode in
Idle mode operation permits the interrupt, serial ports, the 8XC6S2 operates exactly the same as in the 80CSl.
February 1989 2-124

Interrupt System Both external interrupts can be programmed to be level-

activated or transition-activated; an active LOW level al-
The interrupt system is the same as in the 80C51 except lows "Wire-ORing" of several input sources to the input
that the 8XC652 acknowledges interrupt requests from pin.
six sources as follows:
Each interrupt source can be set for either high priority
- INTO external interrupt 0 or low priority. If two separate interrupts are requested
- INTI external interrupt I simultaneously the processor will branch to the vector
- Timer 0 overflow associated with the interrupt that has the higher priority.
- Timer I overflow If there are simultaneous requests from sources that
I2C serial I/O interrupt have the same priority, then the interrupts will be serv-
- UART serial I/O interrupt iced in the following order:
See Figure 60 for a function diagram of the 8XC652 in- I - INTO external interrupt 0
terrupt structure. Each interrupt vectors to a separate 2 - 12C serial I/O interrupt
location in program memory for its service program. 3 - Timer 0 overflow
Each source can be individually enabled or disabled by a 4 - INTI external interrupt I
corresponding bit in the IE register, moreover each in- 5 - Timer I overflow
terrupt may be programmed to a high or low priority 6 - UART serial 1/0 interrupt
level using a corresponding bit in the IP register. Also
all enabled sources can be globally disabled or enabled.
interrupt enable register
interrupt interrupt priority

sources source enable global enable
register
EXTERNAL
~ INTERRUPT
......n.
0- f--
REQUEST 0 ;- """'0- f--
5101 12C 0- f--
INT SERIAL PORT " ;- """'0- f--
INTERNAL
TIMER
0
EXTERNAL
....... . 0-
""0- t--
r--
~ INTERRUPT
.......
~o- r-
REQUEST 1 i' ""'0- r-
INTERNAL
TIMER
.......
0- r--
1 ;- ""'0- t--
5100 INTERNAL iT
SERIAL >- 0- t--
iNT PORT
....... ....... ..........
:R
Figure 60. Interrupt System
February 1989 2-125

A low priority interrupt routine can be interrupted by an Interrupt Priority Register

interrupt having a higher priority. A high priority inter-
rupt can not be interrupted. All of the features of the
7 6 S 4 3 2 1 0
SXC6S2 that have not been discussed in this section are
the same as those on the SOCSl. IP (BSH) - I - IpS11pSOlpTllpX11PTOlpXOI
Interrupt Enable Register Bit Symbol Function

IP.7 Unused
7 6 S 4 3 2 1 0 IP.6 Unused
IP.S PSI SI01 (DC) interrupt priority level
IE (ASH) lEAl - IESIIESOIETlIEX11ETOIEXOI IP.4 PSO SIOO (UART interrupt priority level
IP.3 PTl Timer 1 interrupt priority level
Bit Symbol Fnnction IP.2 PXI Enable interrupt I priority level
1E.7 EA General enable/disable control IP.1 PTO Timer 0 interrupt priority level
o = No interrupt enabled IP.O PXO External interrupt 0 priority level
I = Any individually enabled o = Low priority
interrupt will be accepted 1 = High priority
1E.6 Unused
IE.S ES1 Enable SI01 (I2C) interrupt The following vectors indicate the ROM location where
1E.4 ESO Enable SIOO (UART) interrupt the appropriate interrupt service routine starts.
1E.3 ETl Enable timer I interrupt
1E.2 EXI Enable external 1 interrupt Source Vector
IE.I ETO Enable timer 0 interrupt External 0 (XO) 0003H
IE.O EXO Enable external 0 interrupt Timer 0 overflow (TO) OOOBH
o = interrupt disabled External I (Xl) 0013H
1 = interrupt enabled Timer I overflow (Tl) OOlBH
Serial I/O 0 (UART) (SO) 0023H
Serial I/O I (I2C) (Sl) 002BH
February 1989 2-126

Signetics S83C652/S80C652
Microco ntro lIer

The SB3C652/SBOC652 Single-Chip B-Bit • SC80C51 central processing
Microcontroller is manufactured in an unit
advanced CMOS process and is a de- • 8K x 8 ROM, expandable P1.0;:!; '40 Vee
rivative of the SCBOC51 microcontroller externally to 64K bytes P1.1~ ~PO.O/ADO
family. The SB3C652/SBOC652 has the .256 x 8 RAM, expandable P1.2 3 38 PO.1 / AD1
same instruction set as the BOC51. Two externally to 64K bytes P1.3~ ~7 PO.2/AD2
versions of the derivative exist: • Two standard 16-bit timerl
counters
P1.4~ ~ PO.3/AD3
o SB3C652 - BK bytes mask program- P1.5 B 35 P0.4/AD4
• Four 8-bit I/O ports
mable ROM, 256 bytes RAM • 12C-bus serial I/O port with SCL/P1.B~ ~ PO.5/AD5
o SBOC652 - ROM less version of the byte oriented master and slave SDA/P1.7~ ~ PO.B/ADB
SB3C652 functions RST 9 32 PO.7/AD7
This device provides architectural en-

• Full-duplex UART facilities RXD/DATA/P3.0~ DIP ' ; EA
hancements that make it applicable in a TxD/CL~P3.1~ ~ALE
variety of applications for general control I~P3.2.g ~ Ps"EN
systems. The SB3C652 contains a non- INT1/P3.3~ I¥s P2.7/A15
volatile BK x B read-only program mem- TO/P3.4 ~ ~ P2.6/A14
ory, a volatile 256 x B read/write data 22.!P3.5 ~ ~ P2.5/ A 13
memory, four B-bit I/O ports, two 16-bit
~/P3.6~ ~P2.4/A12
timer/event counters (identical to the
timers of the S80C51), a multi-source, RD/P3.7 ~ ~4 P2.3/A11
two-priority-level, nested interrupt struc- XTAL2~ ~ P2.2/A10
ture, an 12C interface, UART and on-chip XTAL1~ gP2.1/A9
oscillator and timing circuits. For systems Vss~ ~ P2.0/AS
L-_--J-
that require extra capability, the
TOP VIEW
SB3C652 can be expanded using stan-
dard TIL compatible memories and logic. INDEX
,o"~ ,,:' ~r"

The device also functions as an arith-
metic processor having facilities for both
binary and BCD arithmetic plus bit-han-
dling capabilities. The instruction set
consists of over 100 instructions: 49 one- 17 29
byte, 45 two-byte and 17 three-byte.
LOGIC SYM BOL 18 28
With a 12MHz crystal, 5B% of the in-
structions are executed in 1J.1S and 40% TOP VIEW
V.Vee RST
in 2J.1S. Multiply and divide instructions
)0:::~~-)e~~
require 4J.1S. 1 NC 23 NC
24 P2.0/AS
~~ 2
3
P1.0
P1.1 25 P2.1/A9
4 P1.2 26 P2.2/A10
5 P1.3 27 P2.3/A11
6 P1.4 28 P2.4/A12
7 P1.5 29 P2.5/A13
8 SCL/P1.6 30 P2.6/A14
I~
9 SDA/P1.7 31 P2.7/A15
10 RST 32 ~
11 RxD/DAT AlP3.0 33 ALE
12 NC 34 NC
_SCL 13 TxDIICLOCK/P3.1 35 D:
_SDA 14 rnTO/P3.2 36 PO.7/AD7
15 iNTi/P3.3 37 PO.B/AD6
RXD/DATA PO.5/AD5
16 TO/P3.4 38
m
D/CLOCK
TO
17
18
19
T1/P3.5
Wl\/P3.6
lm/P3.7
39
40
41
PO.4/AD4
PO.3/AD3
PO.2/AD2
i
RD
20
21
XTAL2
XTAL1
42
43
PO.1/AD1
PO.O/ADO
Vee
22 Vss 44
February 1989 2-127 95544

CMOS Single-Chip 8-Bit Microcontroller S83C652/S80C652
S8 C852-
1
C CC
T
Custom ROM Pattern No.
Signetics. Contact Signetics
Package and Pins
ROMle.s
S80C652-1 N40
S80C652-1 A44
S80C652-2N40
S80C652-2A44
ROM Version
S83C652-1 N40
S83C652-1A44
S83C652-2N40
S83C652-2A44
Temperature and Package
o to +70 0 C plastic DIP
o to +70 0 C plastic LCC
-40 to +85 0 C plastic DIP
-40 to +85°C plastic LCC

Frequency
1.2 to 12MHz
1.2 to 12MHz
1.2 to 12MHz
1.2 to 12MHz
A44 - 44-Pin Plastic LCC
N40 - 40-Pin Plastic DIP S80C652-4N40 S83C652-4N40 o to +70°C plastic DIP' 1.2 to 16MHz
S80C652-4A44 S83C652-4A44 o to +70°C plastic LCC' 1.2 to 16MHz
Speed and Temperature Range S80C652-5N40 S83C652-5N40 -40 to +85°C plastic DIP' 1.2 to 16MHz
1 - 0 to +70 0 C, 1.2 to 12MHz
2 - -40 to +85 0 C, 1.2 to 12MHz S80C652-5A44 S83C652-5A44 -40 to +85 0 C plastic LCC' 1.2 to 16MHz
4 - 0 to +70 0 C, 1.2 to 16MHz
5 - -40 to +85°C, 1.2 to 16MHz S80C652-6N40 S83C652-6N40 -40 to +11 OOC plastic DIP 1.2 to 12MHz
6 - -40 to +110 0 C, 1.2 to 12MHz S80C652-6A44 S83C652-6A44 -40 to +110 0 C plastic LCC 1.2 to 12MHz
ROMlesa/ROM ·Preliminary specification
0- ROMless
3 - ROM
BLOCK DIAGRAM
FREQUENCY
REFERENCE COUNTERS
I
XTAL2 XTAL1
• I
TO T1
i
PROGRAM DATA
MEMORY MEMORY
(8K x 8 ROM) (258 x 8 RAM)
SDA} SHARED
WITH
SCL PORT 1
INTERNAL
INTERRUPTS
L J
PARALLEL PORTS, I SERIAL IN SERIAL OUT.

ADDRESS/DATA BUS i
EXTERNAL INTERRUPTS AND I/O PINS SHARED WITH
PORT 3
February 1989 2-128


PIN DESCRIPTION
PIN NO.
MNEMONIC 1----,-----1 TYPE NAME AND FUNCTION
DIP LCC
PO.7-PO.0 39-32 43-46 I/O Port 0: 8-bit open-drain bidirectional I/O port. It is also the multiplexed low-order ad-
dress and data bus during accesses to external memory (during these accesses it acti-
vates internal pullups). Port 0 can sink/source 8 LS TTL inputs.
Pl.O-Pl.7 1-8 2-9 I/O Port 1: 8-bit quasi-bidirectional I/O port. Port 1 can sink/source one TTL (- 4 LS TTL)
input. It can drive CMOS inputs without external pullups, except Pl.6 and Pl.7 which
have open drain outputs. Alternate functions include:
Pl.6 7 8 I/O SCL: 12C-bus serial port clock line.
Pl.7 8 9 I/O SDA: 12C-bus serial port data line.
P2.0-P2.7 21-28 24-31 I/O Port 2: 8-bit quasi-bidirectional I/O port with internal pull ups. During access to
external memories (RAM/ROM) that use 16-bit addresses (MOVX @DPTR), port 2 emits
the high-order address byte. When external RAM is accessed with an 8-bit address
(MOVX @Ri), port 2 emits the contents of the P2 function register. Port 2 can sink/
source one TTL (-4 LS TTL) input. It can drive CMOS inputs without external pull ups.
P3.0-P3.7 10-17 ii, I/O Port 3: 8-bit quasi-bidirectional I/O port with internal pull ups. It also serves the follow-
13-19 ing alternative functions:
P3.0 10 11 I RxD/DATA: Serial port receiver data input (asynchronous) or data input/output (syn-
chronous).
P3.1 11 13 o TxD/CLOCK: Serial port transmitter data output (asynchronous) or clock output (syn-
chronous).
P3.2 12 14 I INTO: External interrupt 0 or gate control input for timer/event counter O.
P3.3 13 15 I INT1: External interrupt 1 or gate control input for timer/event counter 1.
P3.4 14 16 I TO: External input for timer/event counter O.
P3.5 15 17 I T1: External input for timer/event counter 1.
P3.6 16 18 o WR: External data memory write strobe.
P3.7 17 19 ORO: External data memory read strobe.
The generation or use of a port pin as an alternative function Is carried out auto-
matically by the S83C652, provided the associated special function register bit Is set
high. Port 3 can sink/source one TTL (-4 LS TTL) input. It can drive CMOS Inputs with-
out external pullups.
RST 9 10 I Reset: A high level on this pin for two machine cycles, while the oscillator is running,
resets the device. An internal pull-down resistor permits power-on reset using only a
capacitor to Vee.
XTAL1 19 21 I Crystal Input 1: Input to the inverting amplifier that forms the oscillator. Left open-
circuit when an external oscillator clock is used.
Vss 20 22 Ground: Circuit ground potential.
PSEN 29 32 o Program Store Enable: Read strobe to the external program memory via port 0 and 2. It
is activated twice each machine cycle during fetches from external..J2!.Q9!am memory.
When executing out of external program memory, two activations of PSEN are skipped
during each access to external data memory. PSEN is not activated (remains high)
during fetches from external program memory. PSEN can sink/source 8 LS TTL inputs.
It can drive CMOS inputs without an external pull up.
ALE 30 33 o Address Latch Enable: Latches the low byte of the address during accesses to external
memory in normal operation. It is activated every six oscillator periods except during an
external data memory access. ALE can sink/source 8 LS TTL inputs. It can drive CMOS
inputs without an external pull up.
31 35 I External Access: When EA is held at a TTL high level, the CPU executes out QLthe
internal program ROM, provided the program counter is less than 8192. When EA is
held at a T1l..low level, the CPU executes out of external program memory via port 0
and port 2. EA is not allowed to float.
Vee 40 44 Power Supply: +5V power supply pin during normal operation, idle mode and power-
down mode.
NOTE:
To avoid a 'latch-up' effect at power-on, the voltage on any pin at any time must not be higher or lower than Vee + 0.5V or
VSS - 0.4V respectively.
February 1989 2-129

OSCILLATOR CHARACTERISTICS RESET idle mode is activated. -The CPU con-

XTAU and XTAL2 are the input and out- A reset is accomplished by holding the tents, the on-chip RAM, and all of the
put, respectively, of an inverting ampli- RST pin high for at least two machine special function registers remain intact
as an on-chip oscillator, as shown in the oscillator is running. To insure a good terminated either by any enabled inter-
logic symbol, page 1. power-on reset, the RST pin must be rupt (at which time the process is picked
To drive the device from an external time to start up (normally a few millisec- continued), or by a hardware reset
clock source, XTAU should be driven onds) plus two machine cycles. At which starts the processor in the same
while XTAL2 is left unconnected. There power-on, the voltage on Vee and RST manner as a power-on reset.
input to the internal clock circuitry is In the power-<lown mode, the oscillator
ever, minimum and maximum high and In the idle mode, the CPU puts itself to power-<lown is the last instruction exe-
must be observed. stay active. The instruction to invoke the RAM are preserved. A hardware reset is
Table 1 shows the state of liD ports


February 1989 2-130


Voltage on any pin to Vss -0.5 to + 6.5 V
1.0 W
NOTES:
1. Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the devicB. This is a stress rating only and
functional operation of the device at these or any conditions other than those described in the AC and DC Electrical Characteristics
section of this specification is not implied.
2. This product includes circuitry specifically desig ned for the protection of its internal devices from the damaging effects of excessive static
noted.
DC ELECTRICAL CHARACTERISTICS TA - O°C to +70°C or TA - -40°C to +85°C/110°C, Vee - 5V ±10%, Vss - OV
TEST LIMITS
CONDITIONS Min Typical 1 Max
Vee Supply voltage 4.5 5.5 V
Power supply current:
Active mode @ 16MHz 11.5 30 rnA
Icc See note 5
Idle mode @ 16MHz 1.3 6.5 rnA
Power down mode 3 50 /lA
Inputs
Input low voltage, except EA, P1,6/SCL,
VIL -0.5 0. 2Vee-0.1 V
P1.7/SDA
VIL1 Input low voltage to EA -0.5 0. 2Vee-0.3 V
VIL2 Input low voltage to P1.6/SCL, P1. 7/SDA7 -0.5 1,5 V
Input high VOltage, except XTAL1, RST,
VIH 0, 2Vee+0 .9 Vee+0.5 V
P1.6/SCL, P1.7/SDA
VIH1 Input high voltage, XTAL 1, RST O· 7Vee Vee+0 .5 V
VIH2 Input high voltage, P1.6/SCL, P1. 7/SDA6 3.0 6.0 V
Logical 0 input current, ports 1, 2, 3, except
-IlL VIN - 0.45V 50 /lA
P1.6/SCL, P1.7/SDA
Logical 1 to 0 transition current, ports 1, 2, 3,
-ITL See note 4 -650 /lA
except P1,6/SCL, P1. 7/SDA
±IIL1 Input leakage current, port 0, EA 0.45V<VI< Vee 10 /lA
OV<VI<6V
±IIL2 Input leakage current, P1.6/SCL, P1. 7/SDA 10 /lA
OV<Vee<5.5V
Outputs
Output low voltage, ports 1, 2, 3, except
VOL IOL - 1.6mA2 0.45 V
P1.6/SCL, P1.7/SDA
VOL1 Output low voltage, port 0, ALE, PSEN IOL - 3,2mA2 0.45 V
VOL2 Output low voltage, P1,6/SCL, P1, 7/SDA IOL - 3.0mA2 0.4 V
VOH Output high voltage, ports 1, 2, 3 -IOH - 60/lA 2.4 V
-IOH - 25/lA 0. 75Vee V
VOH1 Output high voltage (port 0 in external bus -IOH - 400/lA 2,4 V
mode, ALE, PSEN)3 -IOH - 150/lA 0. 75Vee V
February 1989 2-131

I TEST I LIMITS I UNIT

SYMBOL
Outputs (Continued)
PARAMETER
I CONDITIONS
I Min I Typical 1 I Max I
RRST I
Internal reset pulldown resistor I I 50 I I 150 I kQ
IPin capacitance ITest freq - 1 MHz, I 10 pF

Cia TA - 25°C I I I
NOTES:
2. Capacitive loading on ports a and 2 may cause spurious noise to be superimposed on the VOLs of ALE and ports 1 and 3. The noise is due
to external bus capacitance discharging into the port a and port 2 pins when these pins make 1-10-0 transitions during bus operations.
In the worst cases (capacitive loading> 100pF), the noise pulse on the ALE pin may exceed O.BV. In such cases, it may be desirable to
qualify ALE with a Schmitt Trigger, or use an address latch with a Schmitt Trigger STROBE input.
3. Capacitive loading on ports 0 and 2 may cause the VOH on ALE and PSEN to momentarily fall below the O.9VCC specification when the
6. The input threshold voltage of Pl.6 and Pl.? (Sial) meets the 12C specification, so an input voltage below 1.5V will be recognized as a log-
ic 0 while an input voltage above 3.0V will be recognized as a logic 1.
AC ELECTRICAL CHARACTERISTICS TA - O°C to +70°C, or TA - -40°C to +85°C/l10°C, VCC - 5V ±10%, VSS - OV1, 2
Min Max Min Max
Program Memory
l/tCLCL 1 Oscillator frequency 1.2 16 MHz
tLHLL 1 ALE pulse width 127 2tCLCL -40 ns
tLLAX 1 Address hold after ALE low 43 tCLCL-35 ns
tPLIV 1 PSEN low to valid instruction in 145 3tCLCL -105 ns
tPXIX 1 Input instruction hold after PSEN 0 0 ns
Data Memory
tAVLL 2, 3 Address valid to ALE low 43 tCLCL-40 ns
tRLRH 2, 3 RD pulse width 400 6tCLCL -100 ns
tWLWH 2,3 WR pulse width 400 6tCLCL -100 ns
tRLDV 2, 3 RD low to valid data in 252 5tCLCL -165 ns
tRHDZ 2, 3 Data float after R D 97 2tCLCL -70 ns
tLLDV 2, 3 ALE low to valid data in 517 8tCLCL -150 ns
tAVDV 2, 3 Address to valid data in 585 9tCLCL -165 ns
tLLWL 2, 3 ALE low to RD or WR low 200 300 3tCLCL -50 3tCLCL+50 ns
tAVWL 2, 3 Address valid to WR low or RD low 203 4tCLCL -130 ns
tOVWX 2, 3 Data valid to WR transition 23 tCLCL -60 ns
tWHLH 2, 3 RD or WR high to ALE high 43 123 tCLCL -40 tCLCL+40 ns
February 1989 2-132


Min Max Min Max
External Clock
tCHCX 4 High time 3 20 20 ns
tCLCX 4 Low time 3 20 20 ns
tCLCH 4 Rise time 3 20 20 ns
tCHCL 4 Fall time 3 20 20 ns
Shift Register
tXLXL 5 Serial port clock cycle time 3 1.0 12tCLCL lIS
tOVXH 5 Output data setup to clock rising edge 3 700 1OtCLCL -133 ns
tXHOX 5 Output data hold after clock rising edge 3 50 2tCLCL -117 ns
tXHDX 5 Input data hold after clock rising edge 3 0 0 ns
tXHDV 5 Clock rising edge to input data valid 3 700 1OtCLCL -133 ns
NOTES:
1. Parameters are valid over operating tei!!2erature range unless otherwise specified.
2. Load capacitance for port 0, ALE, and PSEN - 100pF, load capacitance for all other outputs - BOpF.
3. These values are characterized but not 100% production tested.

Each timing symbol has five characters. The first character is P- PSEN
positions, indicate the name of a signal or the logical status of R - RD signal
that signal. The designations are: t - Time
A - Address V - Valid
C - Clock W - WR signal
D - I nput data X - No longer a valid logic level
H - Logic level high Z - Float
I - I nstruction (program memory contents) Examples: tAVLL - Time for address valid to ALE low.
L - Logic level low, or ALE tLLPL - Time for ALE low to PSEN low.
ALE
I"SE'N
---"
PORTO _ _ _J
PORT 2
February 1989 2-133

ALE
t-----tLLDV ---.....,
---*~-----tRLRH------.....,
PORTO
~----------~VDV-----~
PORT 2 P2.0-P2.7 OR AB-AI5 FROM DPH A8-A15 FROM PCH
ALE
---to----WLWH----o!
PORTO DATA OUT AO-A7 FROM PCL
PORT 2 P2.0-P2.7 OR A8-A15 FROM DPH AB-AI5 FROM PCH
February 1989 2-134

Vee-O,S .-------,,-- - - -
O.4SV
~---------tCLCL-----~
ALE
tOVXH HI t XHOX
OUTPUT DATA
\ X X~--JX~--JX~--JX'-_...JX'-_...JX'-_...J
f
WRITE TO SBUF
I INPUT DATAl ____________ J, __J~~-'~=7' 1~-'··7' I~-"·~' I~·-"~' I':-"?,. I'''-''~'' ~.

f
CLEAR RI t
SET RI
Vee-O.S
O.4SV
=x O.2Vee+O.9 >C
_,-,O""2""V""e,,,e-...;O;;,;','-'-_.....
Timing
Reference
Points
<
for a logic "1" and 0.4SV for a logic '0'.
a logic '1' and V IL max for a logic '0'.
Figure 6. AC Testing Input/Output Figure 7. Float Waveform
February 1989 2-135

Vee
....._ _ _--ilee
Vee
l Vee
Vee
RST
RST
XTAL2 XTAL2
CLOCK (NC) CLOCK (NC) XTALI
XTALl

0.45V
~---------tCLCL----------~
tCLCH = tCHCL = 5ns
Vee
....._ _ _--il,ee
Vee
l
Vee
RST
(NC) XTAL2
XTALI
Vss

All other pins are disconnected. VCC =
2V to 5.5V
February 1989 2-136

8XC751 OVERVIEW This part is well suited for logic replacement in con-
sumer and industrial applications.
The Signetics 83C751/87C751 offers the advantages of
DIFFERENCES FROM THE 80C5l
the SC80C51 architecture in a small package and at a
low cost. This microcontroller is fabricated with
Memory Organization
Signetics high-density CMOS technology. Signetic~. e.ri-
taxial substrate minimizes CMOS lach-up senSItiVIty. The central processing unit (CPU) manipulates operands
The 83C751187C751 (hereafter referred to collectively as in 2 address spaces as shown in Figure 61. The part's
the 83C751) contains a 2K x 8 ROM/EPROM, a 64 x 8 internal memory space consists of 2K bytes of program
RAM 19 I/O lines a 16-bit auto-reload counter/timer, memory, and 64 bytes of data RAM overlapped with the
a fix~d rate timer,' a five source fixed priority interrupt
128 byte special function register area. The differences
structure, a bidirectional Inter-Integrated Circuit (12C) from the 80C5l are in RAM size (64 bytes vs 128 bytes),
serial bus interface, and an on-chip oscillator. The on- in external RAM access (not available on the 83C751),
board inter-integrated circuit (12C) bus interface allows in internal ROM size (2K bytes vs 4k bytes), and in ex-
the 83C751 to operate as a master or slave device on ternal program memory expansion (not available on the
the 12C small area network. This capability facilitates
83C751). The 128 byte special function register (SFR)
I/O and RAM expansion, access to EPROM, processor space is accessed as on the 80C51 with some of the reg-
to processor communication, and efficient interface to a isters having been changed to reflect changes in the
wide variety of dedicated 12C peripherals. The 83C751
83C751 peripheral functions. The stack may be located
has the following features:
anywhere in internal RAM by loading the 8-bit stack
pointer (SP). It should be noted that stack depth is lim-
ited to 64 bytes, the amount of available RAM. A reset
• Boolean processor
loads the stack pointer with 07F (which is pre-incre-
• Inter-integrated Circuit (12C) serial bus interface
mented on a PUSH instruction).
• Fixed-rate timer
• 16-bit auto reload able counterltimer Special Fnnction Registers
• Small package sizes
- 24 pin DIP (300 mil "skinny DIP") The 83C751 contains many of the Special Function Reg-
- 28 pin PLCC isters (SFR) that are found on the 80C51. Due to the
• 2K x 8 ROM/EPROM different peripheral features on the 83C751, there are
• Available in erasable quartz lid (87C751), one-time several additional SFRs and several that have been
programmable (87C751), or mask programmable changed. There is no port 2 on the 83C751 so the P2
versions (83C751) SFR isn't used. The standard UART found on the 80C51
• Wide oscillator frequency range has been replaced by the 12C serial interface, so the
• Low power consumption: UART SFRs, SCON and SBUF, have been replaced by
- Normal operation: less than llmA @ 5V, 12MHz 12CON and 12DAT, and two additional 12C registers
• Idle mode have been added (12STA and 12CFG).
• Power-down mode
• CMOS and TIL compatible
(FFH) 255
SPECIAL
FUNCTION
REGISTERS
(80H) 128
(3FH) 63
INTERNAL
DATA RAM
(OOH) 0
Figure 61. Memory Map
February 1989 2-137

Because the interrupt structure is single level on the 110 Port Structure
83C751 there is no need for the IP SFR, so it is not
used. The counter/timer has only one mode of operation The 8XC751 has 2 eight-bit ports (ports I and 3) and I
so the TMOD SFR is not used. There is also only one three-bit port (port 0). All three ports on the 8XC751
counter/timer so there is no need for the TLI and THI are bi-directional. Each consists of a latch (special func-
SFRs found on the 80C51. These have been replaced on tion register PO, PI, P3), an output driver, and an input
the 83C751 by RTL and RTH the counter/timer reload buffer. Three Port 1 pins and two Port 0 pins are multi-
registers. Table 20 shows the special function registers, functional. In addition to' being port pins, these pins
their locations, and reset values. serve the function of special features' as follows:
Data Pointer (DPTR) Port Pin Alternate Function

PO.O I2C clock (SCL)
The Data Pointer (DP1R) consists of a high byte (DPH) PO.I I2C data (SDA)
and a low byte (DPL). In the 80C51 this register allows P1.5 INTO (external interrupt 0 input)
the access of external data memory using the MOVX in- P1.6 INTI (external interrupt I input)
struction. Since the 83C751 does not support MOVX or P1.7 TO (timer 0 external input)
external me'mory accesses this register is generally used
as a 16-bit offset pointer of the accumulator in a MOVC Ports I and 3 are identical in structure to the same
instruction. DP1R may also be manipulated as two inde- ports on the 80C51. The structure of Port 0 on the
pendent 8-bit registers. 8XC751 is similar to that of the 80C51 but does not in-
clude address/data input and output circuitry. As on the
110 Port Latches (pO, PI, P3) 80C51, ports 1 and 3 are quasi-bidirectional while port 0
is bi-directional with no internal pullups.
The port latches function the same as those on the
80C51. Since there is no Port 2 on the 83C751 the P2
latch is not used. Port 0 on the 83C751 has only 3 bits,
so only 3 bits of the PO SFR have a useful function.
B 112
~
·1
TL TH TF INT
C/T=1
TO PIN r
TR
GATE
INTO PIN
RTL RTH
Figure 62. 83C7S1 Counterrflmer Block Diagram
February 1989 2-138

Symbol Description Direct Bit Address. Symbol or Alternative Port Function

Address Reset Value
MSB LSB
ACC* Accumulator EOH E7 E6 E5 E4 E3 E2 EI EO DOH
B* B register FOH F7 F6 F5 F4 F3 F2 FI FO DOH
DPH High byte 83H DOH
DPL Low byte 82H DOH
DF DE
DD DC DB DA D9 D8
12CFG*# 12C configuration D8H/RD SLAVE~STRCl[ 0 tIIRUN! - I I CTl I CTO OOOOxxOOB
WR SLAVENlMASTRQlCLRTHIIR UN! - I I CTl I CTO
9F 9E 9D 9C 9B 9A 99 98
I2CON*# I2C control
-
98H/RD RDA'"Q ATN lDRDYI ARL I STR I STP IMASTER! 8lH
WR CXAl IDLE~ CDR ICARLI CSTR I CSTP I XSTR I XSTP
I2DAT# I2C data 99H/RD RDATI 0 I 0 I 0 I 0 I 0 I 0 0 80H

WR XDATI X I X X X X J X ~ X
I2STA*# I2C control F8H 1 IDLE lXDATAIXACTVIMAKSTRIMAKSTPI XSTR I XSTP xOl00000B
IE*# Interrupt enable A8H EAJ 1 I EI2 I ETI I EX1 ETO EXO DOH
PO*# Port 0 80H - - - - - 82 81 80 xxxxxl1lB
PI * Port 1 90H 97 96 95 94 93 92 91 90 FFH
P3* Port 3 BOH B7 B6 B5 B4 B3 B2 Bl BO FFH
PC ON Power control 87H 1 - 1 I - I PD IDL xxxxxxDOB
D7 D6 D5 D4 D3 D2 Dl DO
PSW* Program status word DOH CY 1 AC 1 FO I RSI I RSO I ov I I P DOH
8F 8E 8D 8C 8B 8A 89 88
TCON*# Timer/counter control 88H GATEl CIT 1 TF I TR I lEO I ITO lEI ITl DOH
TL# Timer low byte 8AH DOH
TH# Timer high byte 8CH DOH
RTL# Timer low reload 8BH DOH
RTH# Timer high reload 8DH DOH
* = SFRs are bit addressable.
Timer/Counter TCON Register
The 8XC751 has two timers: a 16-bit Timer/Counter and 7 6 5 432 0

a lO-bit fixed rate timer. The 16-bit Timer/Counter's IGATEI CIT I TF TR lEO ITO lEI I ITI I
operation is similar to Mode 2 operation on the 80C51. MSB LSB
but is extended to 16 bits. The Timer/Counter is clocked GATE 1 - Timer/counter is enabled only when INTO
by either 1/12 the oscillator frequency or by transitions pin is high, and TR is 1.
on the TO pin. The CIT pin in special function register o - Timer/counter is enabled when TR is 1.
TCON selects between these two modes. When the CIT 1 - Counter/timer operation from TO pin.
TCON TR bit is set, the timer/counter is enabled. Regis- o - Timer operation from internal clock.
ter pair TH and TL are incremented by the clock TF I - Set on overflow of TH.
source. When the register pair overflows, the register o - Cleared when processor vectors to interrupt
pair is reloaded with the values in registers RTH and routine and by reset.
RTL. The value in the reload registers is left unchanged. TR 1 - Timer/counter enabled.
See the 83C751 counter/timer block diagram in Figure o - Timer/counter disabled.
62. The TF bit in special function register TCON is set lEO 1 - Edge detected in INTO.
on counter overflow and, if the interrupt is enabled, will
generate an interrupt.
February 1989 2-139

ITO - INTO is edge triggered. The MINIMUM SDA LOW TO SCL LOW time in a
o- INTO is level sensitive. start condition.
lEI 1 - Edge detected on INTI. The MAXIMUM SCL CHANGE time while an 12C
IT1 1 - INTI is edge triggered. frame is in progress. A frame is in progress between
o - INTI is level sensitive. a Start condition and the following Stop condition.
This time span serves to detect a lack of software re-
These flags are functionally identical to the corre- sponse on this 8XC751 as well as external l2C prob-
sponding 80C51 flags, except that there is only one tim- lems. SCL "stuck low" indicates a faulty Master or
er on the 83C751 and the flags are therefore combined Slave. SCL "stuck high" may mean a faulty device, or
into one register. that noise induced onto the 12C caused all Masters to
withdraw from 12C arbitration.
The 12C watchdog timer, timer I, is also available as a
general purpose fixed rate timer when the 12C interface The first 5 of these times are 4.7jlS (see 12C specifica-
is not being used. A clock rate of 1/12 the oscillator tion) and are covered by the low order 3 bits of Timer 1.
frequency forms the input to a prescaler. This prescaler Timer I is clocked by the 8XC751 oscillator which can
c an be programmed for 1 of 4 values to give a range of vary in frequency from 0.5 to 16MHz. A prescaler with
timeout periods (see more discussion in 12C section). one of 4 divisor values allows Timer I values to be opti-
Timer I has a timeout interval of 1024 machine cycles. mized for different oscillator frequencies. At lower fre-
An external reset on this timer is initiated by a transi- quencies, software response time is increased and will
tion on the SCL(PO.O) pin. degrade maximum performance of the 12C bus. For
100Khz bus performance, the oscillator rate should be
12C Serial Interface limited to the 8-16MHz range which is the range that
the Timer I prescaler was designed for. See special
The 12C bus uses two wires (SDA and SCL) to transfer function register 12CFG description for prescale values
information between devices connected to the bus. The (CTO, CTl).
main technical features of the bus are:
The MAXIMUM SCL CHANGE time is important but
- Bidirectional data transfer between masters and slaves its exact span is not critical. The complete 10 bits of
- Serial addressing of slaves Timer I are used to count out the maximum time. When
- Acknowledgment after each transferred byte 12C operation is enabled, this counter is cleared by tran-
- Multimaster bus sitions on the SCL pin. The timer does not run between
- Arbitration between simultaneously transmitting mas- 12C frames (i.e. whenever Reset or Stop occurred more
ters without corruption of serial data on bus recently than the last Start). When this counter is run-
ning, it will carry out after 1024 machine cycles have
A large family of 12C compatible ICs is available. See elapsed since a change on SCL. A carry out causes a
the 12C section of this manual for more details on the hardware reset of the 83C751 12C interface and gener-
bus and available ICs.
ates an interrupt if the Timer I interrupt is enabled. In
cases where the bus hangup is due to a lack of software
The 83C751 12C subsystem includes hardware to simplify
response by this 83C751, the reset releases SCL and al-
the software required to drive the 12C bus. The hardware
lows 12C operation among other devices to continue.
is a single bit interface which in addition to including
the necessary arbitration and framing error checks, in-
I2C Register 12CON
cludes clock stretching and a bus timeout timer. The in-
terface is synchronized to software either through polled 7 6 5 4 3 2 o
loops or interrupts. Six time spans are important in 12C Read
operation and are insured by Timer I:
Write
- The MINIMUM HIGH time for SCL when this de-
vice is the master. Reading 12CON
- The MINIMUM LOW time for SCL when this device
is a master. This is not very important for a single-bit RDAT The data from SDA is captured into "Receive
hardware interface like this one, because the SCL DATa" whenever a rising edge occurs on
low time is stretched until the software responds to SCL. RDAT is also available (with 7 low-
the 12C flags. The software response time normally order zeros) in the 12DAT register. The dif-
meets or exceeds the MIN La time. In cases where ference between reading it here and there is
the software responds within (MIN HI + MIN La) that reading 12DAT clears DRDY, allowing
time, Timer I will insure that the minimum time is the 12C to proceed on to another bit. Typi-
met. cally, the first 7 bits of a received byte are
- The MINIMUM SCL HIGH TO SDA HIGH time in read from 12DAT, while the 8th is read here.
a stop condition. Then, 12DAT can be written to send the Ack
- The MINIMUM SDA HIGH TO SDA LOW time be- bit and clear DRDY.
tween 12C stop and start conditions. (4.7jlS see spec.)
February 1989 2-140

Am "ATteNtion" is 1 when one or more of DRDY, MASTER "MASTER" is 1 if this 83C751 is cur-
ARL, STR, or STP is 1. Thus, Am com- rently a Master on the nc. MASTER
prises a single bit that can be tested to re- is set when MASTRQ is 1 and the bus
lease the I2C service routine from a "wait is not busy (i.e., if a start bit hasn't
loop". been received since Reset or a "Timer
DRDY "Data ReaDY" (and thus Am) is set when a I" time-out, or if a Stop has been re-
rising edge occurs on SCL, except at idle ceived since the last Start). MASTER
Slave. DRDY is cleared by writing CDR ~ 1, is cleared when ARL is set, or after the
or by writing or reading the 12DAT register. software writes MASTRQ ~ 0 and then
The following low period on SCL is stretched XSTP ~ 1.
until the program responds by clearing
DRDY. Writing I2CON
Checking Am and DRDY Typically, for each bit in an I2C message, a service rou-
tine waits for Am ~ 1. Based on DRDY, ARL, STR,
When a program detects Am ~ 1, it should next check and STP, and on the current bit position in the message,
DRDY. If DRDY ~ 1, then if it receives the last bit it it may then write I2CON with one or more of the follow-
should capture the data from RDAT (in 12DAT or ing bits, or it may read or write the I2DAT register.
I2CON). Next, if the next bit is to be sent it should be
written to I2DAT. One way or another it should clear CXA Writing a 1 to "Clear Xmit Active" clears the
DRDY and then return to monitoring Am. Note that if Transmit Active state. (Reading the I2DAT
any of ARL, STR, or STP is set, clearing DRDY will register also does this.)
not release SCL to high, so that the 12C will not go on
to the next bit. If a program detects Am ~ 1, and Regarding Transmit Active
DRDY ~ 0, it should go on to examine ARL, STR, and
STP. Transmit Active is an internal state in the I2C interface
and is not directly testable. Transmit Active is set by
ARL "Arbitration Loss" is 1 when transmit Active writing the I2DAT register, or by writing I2CON with
was set, but this 83C751 lost arbitration to XSTR ~ 1 or XSTP ~ 1. The I2C interface will only
another transmitter. Transmit Active is drive the SDA line low when Transmit Active is set, and
cleared when ARL is 1. There are 4 separate the ARL bit will only be set to 1 when Transmit Active
cases in which ARL is set. is set. Transmit Active is cleared by reading the I2DAT
1. If the program sent a 1 or repeated start, register, or by writing I2CON with CXA ~ 1. Transmit
but another device sent a 0, or a stop, so that Active is automatically cleared when ARL is 1.
SDA is 0 at the rising edge of SCL. (If the
other device sent a Stop, the setting of ARL IDLE Writing 1 to "IDLE" causes a Slave's I2C hard-
will be followed shortly by STP being sent.) ware to ignore the I2C until the next Start
2. If the program sent a 1, but another device condition (but if MASTRQ is 1 then a Stop
sent a repeated start, and it drove SDA low condition will make the 83C751 into a Master).
before the 83C751 could drive SCL low. (This CDR Writing a 1 to "Clear Data Ready" clears
type of ARL is always accompanied by STR ~ DRDY. (Reading or writing the I2DAT regis-
1.) ter also does this.)
3. In Master mode, if the program sent a re- CARL Writing a 1 to "Clear Arbitration Loss" clears
peated Start, but another device sent a 1, and the ARL bit.
it drove SCL low before this 83C751 could CSTR Writing a 1 to "Clear STaRt" clears the STR
drive SDA low. bit.
4. In Master mode, if the program sent Stop, CSTP Writing a to "Clear SToP" clears the STP
but it could not be sent because another de- bit. Note that if one or more of DRDY, ARL,
vice sent a O. STR, or STP is 1, the low time of SCL is
STR "STaRt" is set to a 1 when an I2C Start condi- stretched until the service routine responds by
tion is detected at a non-idle Slave or at a clearing them.
Master. (STR is not set when an idle Slave
becomes active due to a Start bit; the Slave
has nothing useful to do until the rising edge
of SCL sets DRDY.)
STP "SToP" is set to 1 when an I2C Stop condi-
tion is detected at a non-idle Slave or at a
Master. (STP is not set for a Stop condition
at an idle Slave.)
February 1989 2-141


XSTR Writing 1's to "Xmit repeated STaRt" and CDR 12C Register 12CFG
tells the I2C hardware to send a Repeated
Start condition. This should only be at a Mas-
ter. Note that XSTR need not and should not
7 6 5 4 3 2 1 o
be used to send an "initial" (non-repeated) Read
Start; it is sent automatically by the I2C hard- Write ~ ____ ~ ____ ~ _ _- L_ _ ~ __ ~ __ ~ __ ~~
ware. Writing XSTR = 1 includes the effect of

writing I2DAT with XDAT = 1; it sets Trans-
mit Active and releases SDA to high during SLAVEN Writing a 1 to "SLAVe ENable" enables
the SCL low time. After SCL goes high, the the Slave functions of the I2C subsystem. If
I2C hardware waits for the suitable minimum SLAVEN and MASTRQ are 0, the I2C
time and then drives SDA low to make the hardware is disabled. This bit is cleared to
Start condition. o by reset and by an I2C time-out.
XSTP Writing 1's to "Xmit SToP" and CDR tells the MASTRQ Writing a 1 to "MASTRQ" requests mas-
I2C hardware to send a Stop condition. This tership of the I2C. If a frame from another
should only be done at a Master. If there are Master is in progress when this bit is
no more messages to initiate, the service rou- changed from 0 to 1, action is delayed un-
tine should clear the MASTRQ bit in I2CFG to til a stop condition is detected. Then, or
o before writing XSTP with 1. Writing XSTP = immediately if a frame is not in progress,
1 includes the effect of writing I2DAT with a start condition is sent and DRDY is set
XDAT - 0; it sets Transmit Active and drives (thus making ATN 1 and generating an I2C
SDA low during the SCL low time. After SCL interrupt). When a Master wishes to re-
goes high, the I2C hardware waits for the suit- lease mastership status of the I2C, it writes
able minimum time and then releases SDA to a 1 to XSTP in I2CON. MASTRQ is
high to make the Stop condition. cleared by Reset and by an I2C time-out.
CLRTI Writing a 1 to this bit clears the Timer I
I2C Register I2DAT interrupt flag. This bit position always
7 6 5 4 3 2 1 0 reads as a O.
TIRUN Writing a 1 to this bit lets Timer I run; a
I:~~ ~ I IIIIII
Read 0 0 0 0 0 0 zero stops and clears it. Together with
Write X X X X X X SLAVEN, MASTRQ, and MASTER, this
bit determines operational modes as shown
RDAT "Receive DATa" is captured from SDA every in Table 21.
rising edge of SCL. Reading I2DAT also en,o These two bits are programmed as a func-
clears DRDY and the Transmit Active state. tion of the OSC rate, to optimize the MIN
XDAT "Xmit Data" sets the data for the next bit. HI and LO time of SCL when this 83C751
Writing I2DAT also clears DRDY and sets is a master on the I2C. The time value de-
the Transmit Active state. termined by these bits controls both of
these parameters, and also the timing for
Regarding Software Response Time Stop and Start conditions. These bits are
cleared to 00 by reset.
Because the 83C751 can run at 16MHz, and because the
I2C interface is optimized for high-speed operation, it is The value that should be programmed in these bits is
quite likely that an I2C service routine will sometimes given in Table 22, for integer-MHz crystal values. For
respond to DRDY (which is set at a rising edge of SCL) other values, the controlling factor is that the MIN
and write I2DAT before SCL has gone low again. If TIME must be greater than or equal to 4.7I1Sec. (MIN
XDAT were applied directly to SDA, this situation would TIME is a range because 12C events are not synchro-
produce an I2C protocol violation. The programmer need nized to osc/12.)
not worry about this possibility because XDAT is applied
to SDA only when SCL is low. The maximum oscillator frequency (MHz) for a given
en, 0 value is given by:
Conversely, a program that includes an I2C service rou-
tine may take a long time to respond to DRDY. Typi- (oscl12 count - 0.42) *12
cally, an I2C routine operates on a flag-polling basis fosc max =
during a message, with interrupts from other peripheral 4.7
functions enabled. If an interrupt occurs it will delay the The 4.7 in the denominator is the minimum LOW time
response of the 12C service routine. The programmer for 12C in microseconds.
need not worry about this very much either, because the
12C hardware stretches the SCL low time until the serv-
ice routine responds. The only constraint on the response
is that it must not exceed the Timer I time-out, which is
at least 768 microseconds.
February 1989 2-142

Table 21. Interaction of TIRUN with SLAVEN, MASTRQ, and MASTER

SLAVEN,
MASTRQ, TIRUN Operating Mode
MASTER
All 0 0 The 12C interface is disabled. Timer I is cleared and does not run. This is the state assumed after
a reset. If an I2C application wants to ignore the I2C at certain times, it should write SLAVEN,
MASTRQ, and TIRUN all to zero.
All 0 1 The I2C interface is disabled. Timer I operates as a free-running time base. Use this mode only in
non - 12C applications.
Any or all 1 0 The 12C interface is enabled. The 3 low-order bits of Timer I run for min-time generation. but
the hi-order bits do not, so that there is no checking for I2C being 'hung'. This configuration can
be used for very slow 12C operation.
Any or all 1 1 The 12C interface is enabled. Timer I runs during frames on the I2C, and is cleared by trans-
itions on SCL, and by Start and Stop conditions. This is the normal state for I2C operation.
Table 22. CT1, CTO Values

CT1, CTO Values Oscll2 Count Program Memory
Priority
Event Address
10
01
00
11
7
6
5
4
Reset
INTO
Counter/Timer 0
000
003
OOB
Higr
INTI 013
Timer I OlB
I2C Register I2STA 12C 023 Lowest
76543210
Read I - I IDLEIXDATAIXACTVIMAKSTRI MAKSTPIXSTRIXSTPI The interrupt enable register (IE) is used to individually
enable or disable the 5 sources. Bit EA in the interrupt
MSB LSB
enable register can be used to globally enable or disable
This register is read only and reflects the internal status all interrupt sources. The interrupt enable register is de-
of the 12C hardware. IDLE, XSTR, and XSTP reflect scribed below. All other interrupt details are based on
the status of the like named bits in the 12CON register. the SOC51 interrupt architecture.
XDATA The content of the transmitter buffer. Interrupt Enable Register IE

XACfV Transmitter active.
MAKSTR This bit is high while the hardware is
effecting a Start condition. x I EI2 I ETl IEX1 I ETO IEXO I
MAKSTP This bit is high while the hardware is
effecting a Stop condition. Symbol Position Fnnction
XSTR This bit is active while the hardware is EA IE.7 Disables all interrupts. If EA = 0,.1!Q
effecting a repeated Start Condition. interrupt will be acknowledged. If EA
= 1, each interrupt source is indivi-
XSTP This bit is active while the hardware is
dually enabled or disabled by setting
effecting a repeated Stop Condition.
or clearing its enable bit.
IE.6 Reserved
Instruction Set IE.5 Reserved
EI2 IE.4 Enables or disables the 12C interrupt.
The instruction set of the S3C751 is identical to the If ES = 0, the 12C interrupt is dis-
SOC51 except for the instructions: MOVX, LCALL, and abled.
UUMP which are not implemented. ETl IE.3 Enables or disables the Timer I over-
flow interrupt. IF ETl = 0, the Timer
Interrupts I interrupt is disabled.
EX1 IE.2 Enables or disables external interrupt
The SXC751 has 5 interrupt sources with fixed priority 1. If EX1 = 0, external interrupt 1 is
levels. Interrupt sources common to the SOC51 are the disabled.
external interrupts (INTO, INTI) and the timer/counter ETO IE.1 Enables or disables the Timer 0
interrupt (ETO). The 12C interrupt (EI2) and Timer I in- overflow interrupt. If ETO = 0, the
terrupt (ETI) are the other two interrupt sources. Timer 0 interrupt is disabled.
EXO IE.O Enables or disables external interrupt
O. If EXO = 0, external interrupt 0 is
Upon interrupt or reset the program counter is loaded disabled.
with specific values for the appropriate interrupt service
routine in program memory. These values are:
February 1989 2-143

Signetics S83C751
Microcontroller

The Signetics S83C751 offers many of • SC80C51 based architecture
the advantages of the SC80C51 archi- • Inter-Integrated Circuit (12C)
tecture in a small package and at low serial bus interface
cost. • Small package sizes
- 24-pin DIP (300 mil
The S83C751 Microcontroller is fabri- "skinny DIP")
cated with Signetics high-density CMOS - 28-pin PLCC
technology. Signetics' epitaxial substrate • Wide power supply voltage
minimizes CMOS latch-up sensitivity. range
• Wide oscillator frequency range
The S83C751 contains a 2K x 8 ROM, a
64 x 8 RAM, 19 110 lines, a 16-bit
- Normal operation: less
counter/timer, a fixed-rate timer, a five-
than 24mA @ 5V, 12MHz
source fixed-priority interrupt structure, a
- Idle mode
bidirectional Inter-Integrated Circuit (12C)
- Power-down mode
serial bus interface, and an on-chip Vss 12
• 2K x 8 ROM, 64 x 8 RAM
oscillator. • 16-bit counter/timer
The onboard inter-integrated circuit (12C) • Fixed-rate timer
bus interface allows the S83C751 to op-
• Boolean processor INDEX
erate as a master or slave device on the
• CMOS and TTL compatible
• Well suited for logic replace- 4 ~ 26 25
CORNEa:
12C small area network. This capability ment, consumer and industrial
facilitates I/O and RAM expansion, ac- applications
cess to EEPROM, processor-to-proces- PLCC
sor communication, and efficient inter-
face to a wide variety of dedicated 12C 11 19
peripherals. LOGIC SYMBOL 12 18
TOP VIEW
1 P3.4 15 P1.0
2 P3.3 16 P1.1
3 P3.2 17 P1.2
4 P3.1 18 P1.3
5 N.C. 19 P1.4
6 P3.0 20 P1.5iiNi'O
7 PO.2 21 N.C.
8 PO.l/SDA 22 N.C.
9 PO.O/SCL 23 P 1.6/ iN'i'i
10 N.C. 24 P1.7ITO
11 RST 25 P3.7
-j_1m'lI
Ii: -11m
12
13
X2
Xl
26
27
P3.6
P3.5
~ _TO 14 Vss 28 Vee
February 1989 2-144 853-0599 95088

CMOS Single-Chip 8-Bit Microcontroller S83C751
S83C751- ee (CVxxxx) PART NUMBER SELECTION
--r-
Custom ROM Pattern No.
Part Number
S83C751-1 N24
Speed
3.5 to 12MHz
Temperature and Package
o to +70°C, Plastic DIP
Applies to masked ROM versions S83C751-2N24 3.5 to 12MHz -40 to +85°C, Plastic DIP
Signetics. Contact Signetics S83C751-3N24 0.5 to 12MHz o to +70°C, Plastic DIP
S83C751-4N24 3.5 to 16MHz o to +70°C, Plastic DIP
S83C751-5N24 3.5 to 16MHz -40 to +85°C, Plastic DIP
Package Codes:
N24 - Plastic DIP S83C751-1A28 3.5 to 12MHz o to +70°C, Plastic LCC
A28 - Plastic PLCC
S83C751-2A28 3.5 to 12MHz -40 to +85°C, Plastic LCC
Speed and Temperature Range:
1- 3.5 to 12MHz. OoC to +70 0 C S83C751-3A28 0.5 to 12MHz o to + 70°C, Plastic LCC
2- 3.5 to 12MHz. -40°C to +85 °c
3- 0.5 to 12MHz. OOC to +70° C S83C751-4A28 3.5 to 16MHz o to +70°C, Plastic LCC
4- 3.5 to 16MHz. OOC to +70 0 C S83C751-5A28 3.5 to 16MHz -40 to +85°C, Plastic LCC
5- 3.5 to 16MHz. -40°C to +85 °c
BLOCK DIAGRAM
~------------l
lIlT
I
L
P1.o-P1.7
February 1989 2-145

PIN DESCRIPTION
PIN NO.
MNEMONIC I - - - , - - - i TYPE NAME AND FUNCTION
DIP PlCC
Vss 12 14 I Circuit ground potential.
Vee 24 28 I Supply voltage during normal, idle, and power-down operation.
PO.0-PO.2 8-6 9-7 I/O Port 0: Port 0 is a 3-bit open-drain bidirectional port. Port 0 pins that have ones written to
them float, and in that state can be used as high-impedance inputs. Port 0 also serves as
the serial 12C interface as shown in the pinout diagram. When this feature is activated by
software, SCL and SDA are driven low in accordance with the 12C protocol. These pins are
driven low if the port register bit is written with a 0 or if the 12C subsystem presents a O.
The state of the pin can always be read from the port register by the program.
To comply with the 12C specification, PO.O and PO.l are open-drain bidirectional I/O pins
with the electrical characteristics listed in the tables that follow. While these differ from
'standard TTL' characteristics, they are close enough for the pins to still be used as
general-purpose 1/0 in non-12C applications.
7 8 I/O SDA (PO.l) 12C data.
8 9 110 SCl (PO.O) 12C clock.
Pl.0-Pl.7 13-20 15-20, 1/0 Port 1: Port 1 is an 8-bit bidirectional 110 port with internal pullups. Port 1 pins that have
23, 24 ones written to them are pulled high by the internal pullups and can be used as inputs. As
inputs, port 1 pins that are externally pulled low will source current because of the internal
pullups. (See DC electrical characteristics: IILl. Port 1 also serves the special function
features of the SCBOC51 family as listed below:
18 20 INTO CP1.5): External interrupt
19 23 INT1 CP1.6): External interrupt
20 24 TO CP1.7): Timer 0 external input
P3.0-P3.7 5-1 4-1, I/O Port 3: Port 3 is an 8-bit bidirectional 1/0 port with internal pull ups. Port 3 pins that have
23-21 6, ones written to them are pulled high by the internal pullups and can be used as inputs. As
27-25 inputs, port 3 pins that are externally being pulled low will source current because of the
pullups (See DC electrical characteristics: IILl.
RST 9 11 Reset: A high on this pin for two machine cycles while the oscillator is running, resets the
device. An internal diffused resistor to Vss permits a power-on RESET using only an
Xl 11 13 Crystal 1: Input to the inverting oscillator amplifier and input to the internal clock generator
circuits.
X2 10 12 o Crystal 2: Output from the inverting oscillator amplifier.
OSCilLATOR CHARACTERISTICS high long. enough to allow the oscillator POWER-DOWN MODE
Xl and X2 are the input and output, re- time to start up (normally a few millisec- In the power-<1own mode, the oscillator
spectively, of an inverting amplifier onds) plus two machine cycles. At is stopped and the instruction to invoke
which can be configured for use as an power-on, the voltage on Vee and RST power-<1own is the last instruction exe-
on-<:hip oscillator, as shown in the logic must come up at the same time for a cuted. Only the contents of the on-<:hip
symbol. proper start-up. RAM are preserved. A hardware reset is
the only way to terminate the power-
To drive the device from an external IDLE MODE down mode. The control bits for the re-
clock source, Xl should be driven while In the idle mode, the CPU puts itself to duced power modes are in the special
X2 is left unconnected. There are no re- sleep while all of the on-<:hip peripherals function register PCON.
quirements on the duty cycle of the ex- stay active. The instruction to invoke the
terna clock signal, because the input to idle mode is the last instruction executed
the internal clock circuitry is through a in the normal operating mode before the
divide-by-two flip-flop. However, mini- idle mode is activated. The CPU con- Table 1. External Pin Status During
mum and maximum high and low times tents, the on-<:hip RAM, and all of the Idle and Power-Down Modes
specified in the data sheet must be special ·function registers remain intact
observed. Mode Port 0 Port1 Port 2
during this mode. The idle mode can be
terminated either by any enabled inter- Idle Data Data Data
RESET rupt (at which time the process is picked
A reset is accomplished by holding the Power-down Data Data Data
up at the interrupt service routine and
RST pin high for at least two machine continued), or by a hardware reset
cycles (24 oscillator periods), while the
which starts the processor in the same
oscillator is running. To insure a good manner as a power-on reset.
power-on reset, the RST pin must be
February 1989 2-146

DIFFERENCES BETWEEN THE A watchdog timer, called Timer I, is for Special Function Register Addresses
S83C751 AND THE SC80C51 use with the 12C subsystem. In 12C appli- Special function register addresses for
cations, this timer is dedicated to time- the S83C751 are identical to those of
Program Memory the SC80C51, except for the changes
generation and bus monitoring of the
On the S83C751, program memory is listed below:
2048 bytes long and is not externally 12C. In non-12C applications, it is avail-
expandable. Program memory can con- able for use as a fixed timebase.
SC80C51 special function registers not
tain S83C751 instructions and constant present in the S83C751 are TMOO (89),
Interrupt Subsystem - Fixed Priority
data. The only fixed allocations in pro- The I P register and the 2-level interrupt P2 (AO) and IP (B8). The SC80C51 regis-
gram memory are the addresses at which system of the SC80C51 are eliminated. ters TH1, TL1, SCON, and SBUF are
execution is taken up in response to re- Simultaneous interrupt conditions are re- replaced with the S83C751 registers
set and to interrupts, which are as solved by a single-level, fixed priority as RTH, RTL, 12CON, and 120AT, respec-
follows: follows: tively. Additional special function regis-
Program Memory ters are 12CFG (08) and 12STA (F8).
Event Address Highest priority: Pin INTO
Reset 000 Counter/timer flag 0
External INTO 003 Pin INT1
Counter/timer 0 OOB Timer I
External I NT1 013
Lowest priority: Serial1 2C
Timer I 01B
12C serial 023 Serial Communications
The S83C751 contains an 12C serial com-
Counter/Timer Subsystem munications port instead of the SC80C51
The S83C751 has one counter/timer
called timer/counter o. Its operation is UART. The 12C serial port is a single bit
similar to mode 2 operation on the hardware interface with all of the hard-
SC80C51, but is extended to 16 bits with ware necessary to support multimaster
16 bits of autoload. The controls for this and slave operations. Also included are
counter are centralized in a single regis- receiver digital filters and timer (timer I)
ter called TCON. for communication watch-<log purposes.
The 12C serial port is controlled through
four special function registers; 12C con-
trol, 12C data, 12C status, and 12C config-
uration.
Table 2. 12C Special Function Register Addresses
Register Address Bit Address
12C control 12CON 98 9F 9E 90 9C 9B 9A 99 98
12C data 120AT 99 - - - - - - - -

12C configuration 12CFG 08 OF DE DO DC DB OA 09 08
12C status 12STA F8 FF FE FD FC FB FA F9 F8
February 1989 2-147


ABSOLUTE MAXIMUM RATINGS
SYMBOL PARAMETER RATING UNIT
TSTG Storage temperature range -65 to +150 °C

Vee Voltage from Vee to Vss -0.5 to +6.5 V
Vs Voltage from any pin to Vss -0.5 to Vee + 0.5 V
Po Power dissipation 1.0 W
DC ELECTRICAL CHARACTERISTICS TA - O°C to +70°C or TA - -45°C to +85°C. Vee - 4.0V to 6.0V. Vss - 0V3
LIMITS
SYMBOL PARAMETER TEST CONDITIONS UNIT
Min Max
VIL Input low voltage. except SDA. SCL -0.5 . 0. 2Vee-0.1 V
VIH Input high voltage. except XI. RST 0.2Vee+0.9 Vee+0.5 V
VIH1 Input high voltage. XI. RST 0. 7Vee Vee+0.5 V
SDA. SCL:
VIl1 Input low voltage -0.5 0.3Vee V
VIH2 Input high voltage O.7Vee Vee+0.5 V
VOL Output low voltage. ports 1 and 3 10L - 1.6mA 0.45 V
VOl1 Output low voltage. port 0.2 10L - 3.2mA 0.45 V
VOH Output high voltage. ports 1 and 3 10H - -601lA 2.4 V
10H - -251lA 0. 75Vee V
10H - -101lA 0. 9Vee V
Port 0.0 and 0.1 (12C) - Drivers

VOL2 Output low voltage 0.4 V
10L - 3mA
(over Vee range)
Driver. receiver combined:
C CapaCitance 10 pF
IlL Logical 0 input current. ports 1 and 3 VIN - 0.45V -50 IlA
ITL Logical 1 to 0 transition current. ports 1 and 38 VIN - 2V -650 IlA
ILl Input leakage current. port 0 0.45 < VIN < Vee ±10 IlA
RRST Reset pull-down resistor 25 175 kohm
CIO Pin capacitance Test Ireq - lMHz. 10 pF
TA - 25°C
Ipo Power-down current4 Vee - 2 to 6.0V 50 IlA
Icc Supply current (see Figure 3)
February 1989 2-148

.CMOS Single-Chip 8-Bit Microcontroller S83C751

AC SYMBOL DESIGNATIONS H - Logic level high
Each timing symbol has five characters. The first character is L - Logic level low
always 'I' (- time). The other characters, depending on their Q - Output data
positions, indicate the name of a signal or the logical status of T - Time
that signal. The designations are; V- Valid
C - Clock X- No longer a valid logic level
AC ELECTRICAL CHARACTERISTICS TA - DoC to +70°C or TA - -45°C to +85°C , VCC - 5V±20%, Vss - OV3, 7
12MHz VARIABLE CLOCK

Min Max Min Max
3.5 12
1/tCLCL Oscillator frequency 3.5 16 MHz
0.5 12
External clock (Figure 1)

tCHCH High time 20 ns
tCLCL Low time 20 ns
tCLCH Rise time 20 ns
tCHCL Fall time 20 ns
NOTES:
functional operation of the device at these Of any other conditions than those described in the AC and DC Electrical Characteristics
2. This product includes circuitry specifically designed for the protection of its internal devices from damaging effects of excessive static
3. Parameters are valid over operating temperature range unless otherwise specified. All voltages with respect to Vss unless otherwise noted.
4. Power-down ICC is measured with all output pins disconnected; port 0 - VCC; X2. XI n.C.; RST = VSS.
5. Active ICC is measured with all output pins disconnected; XI driven with tCLCH, tCHCL - 5ns, VIL - VSS + O.5V, VIH - VCC - O.5V; X2
n .C.; RST - port 0 - VCC. ICC will be slig htly hig her if a crystal oscillator is used.
6. Idle ICC is measured with all output pins disconnected; XI driven with tClCH. tCHCL - 5ns. VIL - VSS + O.5V. VIH - VCC - O.5V; X2 n.c.;
port 0 - VCC; RST - Vss.
7. Load capacitance for ports - 80pF.
8. Pins of ports 1 and 3 source a transition current when they are being externally driven from 1 to O. The transition current reaches its
~O.2'1Cc+o.&
0.2 'ICc -0.1
OA6V
Figure 1. External Clock Drive Waveform
O.45V
~0.2 'ICc +0.&
_ _ _ _ _ _...,,~O.2 'ICc ~.1 x'--___
Figure 2. AC Testing Input/Output Waveform
February 1989 2-149

22 MAX ACTIVE lee 5
20
/
/
18
16 /
14
/
t
< 12 V TYP ACTIVE lee5
E
~ 10
/ ./'
8
./
/' '"
--
8
,,/
4
,,/
-
MAX IDLE lee 8
2 TYP IDLE lee 8
I-"
4 8 12 18
FREQ - MHz

Maximum Icc values taken at Vcc =
B.OV and worst case temperature.
Typical Icc values taken at Vcc =
5.0V and 25°C.
Notes 5 and B refer to AC Electrical Characteristics.
February 1989 2-150

Signetics S87C751
Microcontroller

The Signetics S87C751 offers many of • EPROM version of S83C751
the advantages of the SC80C51 archi- • SC80C51 based architecture
tecture in a small package and at low • Inter-Integrated Circuit (12C) P3.4/A4 1
cost. serial bus interface
• Small package sizes
The S87C751 Microcontroller is fabri-
cated with Signetics high-density CMOS
- 24 pin DIP (300 mil
"skinny DIP")
P3. 2I t;b 3
technology. Signetics epitaxial substrate P3.1/Al~ 4

- 28 pin PLCC
minimizes CMOS latch-up sensitivity. • Available in erasable quartz lid P3.0/AOI 5
or one-time programmable AS
The S87C751 contains a 2K x 8 PO.2/vpp 6
plastic packages
EPROM, a 64 x 8 RAM, 19 I/O lines, a PO.1/SDAI
16-bit auto-reload counter/timer, a fixed- OE-PGM 7
rate timer, a five-source fixed-priority
- Normal operation: less po.O/~fk~ S
interrupt structure, a bidirectional I nter-
Integrated Circuit (12C) serial bus inter-
- Idle mode
face, and an on~hip oscillator.
- Power-down mode
The onboard inter-integrated circuit (12C) • 2K x 8 EPROM, 64 x 8 RAM
bus interface allows the S87C751 to op-
• 16-bit auto reloadable counterl
erate as a master or slave device on the
timer
• Fixed-rate timer
12C small area network. This capability TOP VIEW
facilitates I/O and RAM expansion, ac- INDEX
cess to EEPROM, processor-to-proces-
• Well suited for logic replace-
ment, consumer and industrial COR4 NEa
26: 25 ~
face to a wide variety of dedicated 12C applications
peripherals. PLCC
LOGIC SYMBOL 11 19
12 18
TOP VIEW
1 P3.4/A4 15 P1.0/DO
2 P3.3/A3 16 P1.1/D1
3 P3.21 A21 A10 17 P1.2/D2
4 P3.1/A1/A9 18 P1.3/D3
5 N.C. 19 P1.4/D4
6 P3.0/AO/A8 20 P1.5!mTbID5
7 PO.2/vpp 21 N.C.
8 PO.1/SDAI 22 N.C.
OE-PGM 23 P1.6!11ilTl ID6
9 PO.O/SCll 24 P1.7/TO/D7
ASEL 25 P3.7/A7
10 N.C. 26 P3.6/AS
11 RST 27 P3.5/A5
12 X2 28 Vee
13 X1
14 Vss
February 1989 2-151 853-0600 95089

CMOS Single-Chip 8-Sit Microcontroller S87C751

S87C751-
L~ou~~~.
Part Number Speed Temperature and Package
S87C751-1F24 3.5 to 12MHz o to +70·C. Ceramic DIP
S87C751-3F24 0.5 to 12MHz o to +70·C. Ceramic DIP
S87C751 4F24 3.5 to 16MHz o to +70°C. Ceramic DIP
S87C751-1N24 3.5 to 12MHz o to +70·C. Plastic DIP
S87C751 2N24 3.5 to 12MHz -40 to +85·C. Plastic DIP
S87C751-3N24 0.5 to 12MHz o to +70·C. Plastic DIP
F24 - Ceramic DIP
N24 - Plastic DIP (OTP) S87C751-4N24 3.5 to 16MHz o to +70·C. Plastic DIP
A28 - Plastic PLCC (OTP) S87C751 5N24 3.5 to 16MHz -40 to +85·C. Plastic DIP'
Speed and Temperature Range: S87C751-1A28 3.5 to 12MHz o to +70·C. Plastic LCC'
1 - 3.5 to 12MHz. O·C to +70·C S87C751-2A28 3.5 to 12MHz -40 to +85·C. Plastic LCC'
2 - 3.5 to 12MHz. -40·C to +85 ·C
3 - 0.5 to 12MHz. O·C to +70· C S87C751-3A28 0.5 to 12MHz o to +70·C. Plastic LCC'
4 - 3.5 to 16MHz. O·C to +70· C S87C751 4A28 3.5 to 16MHz o to +70·C. Plastic LCC'
5 - 3.5 to 16MHz. -40·C to +85 ·C S87C751-5A28 3.5 to 16MHz -40 to +85·C. Plastic LCC'
..
'Prellmmary Speclflcallon
BLOCK DIAGRAM
"I
I
PCON I2CFG I_A TeON

I A I IE
THO 11.0
RTH RrL
RST
I
L J
February 1989 2-152

S ignetics Microprocessor Products Product Specification
PIN CONFIGURATION
PIN NO.
MNEMONIC r----.---l TYPE NAME AND FUNCTION
DIP PLCC
Vss 12 14 I Circuit ground potential.
Vee 24 28 I Supply voltage during normal, idle, and power-down operation.
PO.0-PO.2 8-6 9-7 I/O Port 0: Port 0 is a 3-bit open-drain bidirectional port. Port 0 pins that have ones written to
them float, and in that state can be used as high-impedance inputs. Port 0 also serves as
the serial 12C interface as shown in the pinout diagram. When this feature is activated by
software, SCL and SDA are driven low in accordance with the 12C protocol. These pins are
driven low if the port register bit is written with a 0 or if the 12C subsystem presents a O.
The state of the pin can always be read from the port register by the program.
To comply with the 12C specification, PO.O and PO.l are open drain bidirectional I/O pins
with the electrical characteristics listed in the tables that follow. While these differ from
'standard TIL' characteristics, they are close enough for the pins to still be used as
general-purpose I/O in non-12C applications.
Port 0 also provides alternate functions for programming the EPROM memory as follows:
6 7 N/A Vpp (PO.2) - Programming voltage input.
7 8 I OE/PGM (PO.1) - input, OE/PGM, which specifies verify mode (output enable) or the pro-
gram mode.
OE/PGM - 1 output enabled (verify mode)
OE/PGM - 0 program mode.
8 9 ASEL (PO.O) - input which indicates which bits of the EPROM address are applied to port 3.
ASEL - 0 low address byte available on port 3.
ASEL - 1 high address byte is available on port 3 (only the three least significant bits are
used).
7 8 I/O SDA (PO.l) 12C data.
8 9 I/O SCL (PO.O) 12C clock.
Pl.0-Pl.7 13-20 15-20, I/O Port 1: Port 1 is an 8-bit bidirectional I/O port with internal pullups. Port 1 pins that have
23, 24 ones written to them are pulled high by the internal pull ups and can be used as inputs. As
inputs, port 1 pins that are externally pulled low will source current because of the internal
pullups. (See DC electrical characteristics: ilL). Port 1 serves to output the addressed
EPROM contents in the verify mode and accepts as inputs the value to program into the
selected address during the program mode.
Port 1 also serves the special function features of the SC80C51 family as listed below:
18 20 INTO (P1.5): External interrupt
19 23 INT1 (P1.6): External interrupt
20 24 TO (P1.7): Timer 0 external input
P3.0-P3.7 5-1 4-1, I/O Port 3: Port 3 is an 8-bit bidirectional I/O port with internal pullups. Port 3 pins that have
23-21 6, ones written to them are pulled high by the internal pullups and can be used as inputs. As
27-25 inputs, port 3 pins that are externally being pulled low will source current because of the
pullups (See DC electrical characteristics: IlL). Port 3 also functions as the address input
for the EPROM memory location to be programmed (or verified). The ll-bit address is
multiplexed into this port as specified by PO.O/ASEL.
RST 9 11 Reset: A high on this pin for two machine cycles while the oscillator is running resets the
device. An internal diffused resistor to VSS permits a power-on RESET using only an
external capacitor to Vee. After the device is reset, a 10-bit serial sequence, sent LSB first,
applied to RESET, places the device in the programming state allowing programming ad-
dress, data and Vpp to be applied for programming or verification purposes. The RESET
serial sequence must be synchronized with the Xl input.
Xl 11 13 Crystal 1: Input to the inverting oscillator amplifier and input to the internal clock generator
circuits. Xl also serves as the clock to strobe in a serial bit stream into RESET to place the
device in the programming state.
X2 10 12 o Crystal 2: Output from the inverting oscillator amplifier.
February 1989 2-153

OSCILLATOR CHARACTERISTICS POWER-DOWN MODE A watchdog timer, called Timer I, is for

Xl and X2 are the input and output, re- In the power.<Jown mode, the oscillator use with the 12C subsystem. In 12C appli-
spectively, of an inverting amplifier is stopped and the instruction to invoke cations, this timer is dedicated to time-
which can be configured for use as an power.<Jown is the last instruction exe- generation and bus monitoring of the
on-chip oscillator. cuted. Only the contents of the on-chip 12C. In non-12C applications, it is avail-
RAM are preserved. A hardware reset is able for use as a fixed timebase.
To drive the device from an external the only way to terminate the power-
clock source, Xl should be driven while down mode. The control bits for the re- Interrupt Subsystem - Fixed Priority
X2 is left unconnected. There are no reduced power modes are in the special The I P register and the 2-1evel interrupt
quirements on the duty cycle of the ex- function register PCON. system of the SCSOC51 are eliminated.
ternal clock signal, because the input to Simultaneous interrupt conditions are re-
the internal clock circuitry is through a Table 1. External Pin Status During solved by a single-level, fixed priority as
dlvide-by-two flip-flop. However, mini- Idle and Power-Down Modes follows:
mum and maximum high and low times
specified in the data sheet must be Mode PortO Port1 Port 2 Highest priority: Pin INTO
observed. Counterltimer flag 0
Idle Data Data Data
Data Pin INn
Power-down Data Data
RESET Timer I
A reset is accomplished by holding the Lowest priority: Serial12C
RST pin high for at least two machine DIFFERENCES BETWEEN THE
cycles (24 oscillator periods), while the S87C751 AND THE SC80C51 Serial Communications
oscillator is running. To Insure a good The SS7C751 contains an 12C serial com-
power-on reset, the RST pin must be Program Memory
On the SS7C751, program memory is munications port instead of the SCSOC51
high long enough to allow the oscillator UART. The 12C serial port is a single bit
204S bytes long and is not externally
time to start up (normally a few millisec- hardware interface with all of the hard-
expandable. Program memory can con-
onds) plus two machine cycles. At ware necessary to support multimaster
tain SS7C751 instructions and constant
power-on, the voltage on Vee and RST data. The only fixed locations in program and slave operations. Also included are
must come up at the same time for a receiver digital filters and timer (timer I)
memory are the addresses at which exe-
proper start-up. for communication watch.<Jog purposes.
cution is taken up in response to reset
and to interrupts, which are as follows: The 12C serial port is controlled through
IDLE MODE
In the idle mode, the CPU puts itself to Program Memory four special function registers; 12C con-
sleep while all of the on-chip peripherals Event Address trol, 12C data, 12C status, and 12C config-
stay active. The instruction to invoke the Reset 000 uration.
Idle mode is the last Instruction executed External INTO 003
In the normal operating mode before the Counter/timer 0 OOB Special Function Register Addresses
External INTi 013 Special function register addresses for
idle mode Is activated. The CPU con-
Timer I 01B the SS7C751 are identical to those of
tents, the on-chip RAM, and all of the
special function registers remain intact 12C serial 023 the SCSOC51 , except for the changes
during this mode. The Idle mode can be listed below:
CounterlTimer Subsystem
terminated either by any enabled inter- The SS7C751 has one counter/timer SCSOC51 special function registers not
rupt (at which time the process is picked called timer/counter O. Its operation is present in the SS7C751 are TMOD (S9),
up at the interrupt service routine and similar to mode 2 operation on the P2 (AO) and IP (BS). The SCSOC51 regis-
continued), or by a hardware reset SCSOC51, but is extended to 16 bits with ters TH 1, TL1, SCON, and SBUF are
which starts the processor in the same 16 bits of autoload. The controls for this replaced with the SS7C751 registers
manner as a power-on reset. counter are centralized in a single regis- RTH, RTL, 12CON, and 12DAT, respec-
ter called TCON. tively. Additional special function regis-
ters are 12CFG (OS) and 12STA (FS).
Table 2. 12C Special Function Register Addresses

12C control 12CON 9S 9F 9E 90 9C 9B 9A 99 9S
12C data 12DAT 99 - - - - - - - -

12C configuration 12CFG 08 OF DE DO DC DB DA 09 OS
12C status 12STA FS FF FE FD FC FB FA F9 FS
February 19S9 2-154


Vee Voltage from Vee to Vss -0.5 to +6.5 V
Vs Voltage from any pin to Vss -0.5 to Vee + 0.5 V
Vpp Voltage on Vpp pin to Vss Oto+13.0 V
DC ELECTRICAL CHARACTERISTICS TA - O°C to +70°C or TA - -40°C to +85°C, Vee - 4.5V to 5.5V, Vss - OV3
LIMITS
Min Max
VIL Input low voltage, except SDA, SCl -0.5 0. 2Vee-0 .1 V
VIH Input high voltage, except X1, RST 0. 2Vee+0 .9 Vee+0.5 V
VIH1 Input high voltage, X1, RST 0. 7Vee Vee+0.5 V
SDA, SCl:
VIL1 Input low voltage -0.5 0. 3Vee V
VIH2 Input high voltage 0. 7Vee Vee+0.5 V
VOL Output low voltage, ports 1 and 3 IOL - 1.6mA 0.45 V
VOl1 Output low voltage, port 0.2 IOL - 3.2mA 0.45 V
VOH Output high voltage, ports 1 and 3 IOH - -60j.iA 2.4 V
IOH - -25j.iA 0. 75Vee V
IOH - -10j.iA 0.9Vee V
Port 0.0 and 0.1 (12C) - Drivers

VOL2 Output low voltage IOL - 3mA 0.4 V
(over Vee range)
Driver, receiver combined:
C Capacitance 10 pF
IlL logical 0 input current, ports 1 and 3 VIN - 0.45V -50 j.iA
ITL logical 1 to 0 transition current, ports 1 and 38 VIN - 2V -650 j.iA
III Input leakage current, port 0 0.45 < VIN < Vee ±10 j.iA
CIO Pin capacitance Test freq - 1 MHz, 10 pF
TA - 25°C
Ipo Power-down current4 Vee - 2 to 5.5V 50 j.iA
Vpp Vpp program voltage Vss - OV 12.5 13.0 V
Vee - 5V±10%
T A - 21°C-2rC
Ipp Program current Vpp - 13.0V 10 rnA
Icc Supply current (see Figure 3)
February 1989 2-155

AC SYMBOL DESIGNATIONS H - Logic level high

Each timing symbol has five characters. The first character is L- Logic level low
positions, indicate the name of a signal or the logical status of T- Time
that signal. The designations are: V- Valid
C - Clock X- No longer a valid logic level
o - Input data Z - Float
AC ELECTRICAL CHARACTERISTICS TA - O°C to +70°C or TA - -40°C to +BSoC, VCC - SV±10%, Vss - OV3, 7

Min Max Min Max
3.S 12
1/tCLCL Oscillator frequency 3.S 16 MHz
O.S 12

tCLCH Rise time 20 ns
NOTES:
functional operation of the device at these or any other conditions than those described in the AC and DC Electrical Characteristics
4. Power-down Icc is measured with all output pins disconnected; port 0 - VCC; X2, X1 n.c.: RST - VSS.
5. Active ICC is measured with all output pins disconnected; X1 driven with tCLCH, tCHCL - 5ns, VIL - Vss + O.5V, VIH - VCC - O.5V; X2
n.C.; RST - port 0 - VCC. ICC will be slightly higher if a crystal oscillator is used.
6. Idle Icc is measured with all output pins disconnected; X1 driven with tCLCH, tCHCL - 5ns. VIL - Vss + O.5V, VIH - VCC - O.5V; X2 n.c.;
port 0 - VCC; RST - VSS.
7. Load capacitance for ports - 80pF.
8. Pins of ports 1 and 3 source a transition current when they are being externally driven from 1 to O. The transition current reaches its
Vee -o.s
~O.2 IQ:+o,g
OMiV
0.2 IQ: ~.1
Vee -o.s
V0.2 \o\::c -H),g X
_ _ _ _ _....~I"'._""O.2;::.,,;:\o\::c""--(),..;;.;.I-------...... "._ _ _ _ __
OAIIV
February 19B9 2-156

22 MAX ACTIVE lee 5
20
/
V
16
16
/
14
/
f
c( 12 V TYP ACTIVE lee 5
E
~ 10
/ /
8
/
//
--
6
Y"
4
--
Y" MAX IDLE lee 6
2
4 8 12
- TYP IDLE lee 6
16
FREQ - MHz

Maximum Icc values taken at Vcc =
5.5V and worst case temperature.
Typical Icc values taken at Vcc = 5.0V and 25°C.
Notes 5 and 6 refer to AC Electrical Characteristics.
February 1989 2-157

PROGRAMMING CONSIDERATIONS these pins function as normal quasi- Encryption Key Table "
bidirectional I/O ports and the program- The 87C751 includes a 16 byte EPROM
EPROM Characteristics ming equipment may pull these lines low. array that is programmable by the end
The 87C751 is programmed by using a However, prior to sending the 10 bit user. The contents of this array can then
modified Quick-Pulse Programming algo- code on the reset pin, the programming be used to encrypt the program memory
rithm similar to that used for devices equipment should drive these pins high contents during a program memory verify
such as the 87C451 and 87C51. It differs (VIH). The RESET pin may now be used operation. When a program memory ver-
from these devices in that a serial data as the serial data input lor the data ify operation is performed, the contents
stream is used to place the 87C751 in stream which places the 87C751 in the of the program memory location is
the programming mode. programming mode. Data bits are XNOR'ed with one of the bytes in the 16
sampled during the clock high time and byte encryption table. The resulting data
Figure 4 shows a block diagram of the pattern is then provided to port 1 as the
thus should only change during the time
programming configuration for the
that the clock is low. Following transmis- verify data. The encryption mechanism
87C751. Port pin PO.2 is used as the
sion of the last data bit, the RES ET pin can be disabled, in essence, by leaving
programming voltage supply input (Vpp
should be held low. the bytes in. the encryption table in their
signal). Port pin PO.l is used as the pro-
erased state (FFH) since the XNOR
gram (PGM/) signal. This pin is used for Next the address information for the lo- product of a bit with a logical one wiU
the 25 programming pulses. cation to be programmed is placed on result in the original bit. The encryption
port 3 and ASEL used to pertorm the bytes are mapped with the code memory
Port 3 is used as the address input for
address multiplexing, as previously de- in 16 byte groups. The first byte in code
the byte to be programmed and accepts
scribed. At this time, port 1 functions as memory will be encrypted with the first
both the high and low components of the
an output. byte in the encryption table; the second
eleven bit address. Multiplexing of these
address components is pertormed using byte in code memory will be encrypted
A high voltage Vpp level is then applied with the second byte in the encryption
the ASEL input. The user should drive to the Vpp input (PO.2). (This sets Port 1
the ASEL input high and then drive port table and so forth up to and including
as an input port.). The data to be pro- the sixteenth byte. The encryption re-
3 with the high order bits of the address. grammed into the EPROM array is then
ASEL should remain high for at least 13 peats in 16 byte groups; the seventeenth
placed on Port 1. This is followed by a byte in the code memory will be en-
clock cycles. ASEL may then be driven series of programming pulses applied to
low which latches the high order bits of crypted with the first byte in the encryp-
the PGM/ pin (PO.f). These pulses are tion table, and so forth.
the address internally. The high address created by driving PO.l low and then
should remain on port 3 for at least two high. This pulse is repeated until a total Security Bits
clock cycles after ASEL is driven low. of twenty-five programming pulses have Two security bits, security bit 1 and se-
Port 3 may then be driven with the low occurred. At the conclusion of the last curity bit 2, are provided to limit access
byte of the address. The low address wiU pulse, the PG MI signal should remain to the USER EPROM and encryption
be internally stable 13 clock cycles later. high. key arrays. Security bit 1 is the program
The address will remain stable provided inhibit bit, and once programmed per-
that the low byte placed on port 3 is The Vpp signal may now be driven to the forms the following functions:
held stable and ASEL is kept low. Note: VOH level, placing the 87C751 in the 1. Additional programming of the US-
AS EL needs to be pulsed high only to verify mode. (Port 1 is now used as an ER EPROM is inhibited.
change the high byte of the address. output port.). After 4 machine cycles (48 2. Additional programming of the en-
clock periods) the contents of the ad- cryption key is inhibited.
Port 1 is used as a bidirectional data bus dressed location in the EPROM array will
during programming and verify opera- 3. Verification of the encryption key is
appear on Port 1. inhibited.
tions. During the programming mode, it
accepts the byte to be programmed. 4. Verification of the USER EPROM and
The next programming cycle may now
During the verify mode, it provides the the security bit levels may still be
be initiated by placing the address infor-
contents of the EPROM location speci- performed.
mation at the inputs of the multiplexed
fied by the address which has been sup- buffers, driving the Vpp pin to the Vpp (If the encryption key array is being
plied to Port 3. voltage level, providing the byte to be used, this security bit should be pro-
programmed to Port 1 and issuing the 25 grammed by the user to prevent un-
The XTALl pin is the oscillator input and programming pulses on the PGMI pin,
receives the master system clock. This authorized parties from reprogramming
bringing Vpp back down to the Vee level the encryption key to all logical zero
clock should be between 1.2 and 6 and verifying the byte.
MHz. bits. Such programming would provide
data during a verify cycle that is the
Programming Modes
The RESET pin is used to accept the logical compliment of the USER EPROM
The 87C751 has lour programming fea-
serial data stream that places the contents.)
tures incorporated within its EPROM ar-
87C751 into various programming modes. ray. These include the USER EPROM for
This pattern consists of a 10-bit code Security bit 2, the verify inhibit bit, pre-
storage of the application's code, a six- vents verification of both the USER
with the LSB sent first. Each bit is syn- teen byte encryption KEY array and two
chronized to the clock input, Xl. EPROM array and the encryption key
security bits. Programming and verifica- arrays. The security bit levels may still
tion of these four elements are selected be verified.
Programming Operation
by a combination of the serial data
Figures 5 and 6 show the timing dia-
stream applied to the RES ET pin and the
grams for the program/verify cycle.
voltage levels applied to port pins PO.1
RES ET should initially be held high for at
and PO.2. The various combinations are
least two machine cycles. PO.l (pGM/)
shown in Table 3.
and PO.2 (Vpp) will be al VOH as a result
of the RESET operation. At this point,
February 1989 2-158

Programming and Verifying Port 1.7 contains the security bit 1 data tent erasure. For this and secondary ef-
Security Bits and is a logical one if programmed and a fects, it is recommended that an
Security bits are programmed employing logical zero if erased. Likewise, Pl.6 opaque label be placed over the win-
the same techniques used to program contains the security bit 2 data and is a dow. For elevated temperature or sol-
the USER EPROM and KEY arrays using logical one if programmed and a logical vent environments, use Kapton tape
serial data streams and logic levels on zero if erased. Fluorglas part number 2345-5 or equiv-
port pins indicated in Table 3. When pro- alent.
gramming either security bit, it is not Erasure Characteristics
necessary to provide address or data in- Erasure of the EPROM begins to occur The recommended erasure procedure is
formation to the 87C751 on ports 1 and when the chip is exposed to light with exposure to ultraviolet light (at 2537
3. wavelengths shorter than approximately angstroms) to an integrated dose of at
4,000 angstroms. Since sunlight and least 15W-sec/cm2. Exposing the
Verification occurs in a similar manner fluorescent lighting have wavelengths in EPROM to an ultraviolet lamp of
using the RES ET serial stream shown in this range, exposure to these light 12,OOO).LW/cm2 rating for 20 to 39 min-
Table 3. Port 3 is not required to be sources over an extended time (about 1 utes, at a distance of about 1 inch,
driven and the results of the verify op- week in sunlight, or 3 years in room level should be sufficient.
eration will appear on ports 1.6 and 1.7. fluorescent lighting) could cause inadver-
Erasure leaves the array in an all ls
state.
Table 3. Implementing Program/Verify Modes
Operation Serial Code PO.1 (PGM/) PO.2 (Vpp)
Program user EPROM 296H

-0
Vpp
Program key EPROM 292H -0
Vpp
Verify key EPROM 292H VIH VIH
Program security bit 1 29AH -0
Vpp
Program security bit 2 298H -0
Vpp
NOTE:
°Pulsed from VIH to VIL and returned to V1H.
EPROM PROGRAMMING AND VERIFICATION CHARACTERISTICS TA - 21°C to +27°C, VCC - 5V±10%, VSS - OV

1/tCLCL Oscillator/clock frequency 1.2 6 MHz
tAVGL ° Address setup to PO.l (PROG-) low 10).LS + 24tCLCL
tGHAX Address hold after PO.l (PROG-) high 48tCLCL
tDVGL Data setup to PO.l (PROG-) low 38tCLCL
tGHDX Data hold after PO.1 (PROG-) high 36tCLCL
tSHGL Vpp setup to PO.l (PROG-) low 10 ).LS
tGHSL Vpp hold after PO.l (PROG-) 10 ).LS
tGLGH PO.1 (PROG-) width 90 110 ).LS
00
tAVQV Vpp low (Vce> to data valid 48tCLCL
tGHGL PO.1 (PROG-) high to PO.l (PROG-) low 10 ).LS
tSYNL PO.O (sync pulse) low 4tCLCL
tSYNH PO.O (sync pulse) high 8tCLCL
tMASEL ASEL high time 13tCLCL
tMAHLD Address hold time 2tCLCL
tHASET Address setup to ASEL 13tCLCL
tADsTA Low adress to address stable 13tCLCL
NOTES:
°Address should be valid at least 24tCLCL before the rising edge of PO.2 (Vpp).
oOFor a pure verify mode, i.e., no program mode in between, tAVQV is 14tCLCL maximum.
February 1989 2-159

117C7II!
Vee 10--- +5V

AO-A7/A&-A!O P3.O-P;J.7
Vss
~
ADDAESS STROBE PO.OIASEL
Pl.CI-P!.7 DATA BUS
PROGRAMIIING
PULSES PD.!
vpp /VIH VOLTAGE P0.2
501J1CE
cue
q
50URCE XTALI
RESET
COHIROL I RESET
LOGIC I
Figura 4. Programming Configuration
lCTAL 1
~ 2 MACHINE
...---CYClES _I_ TEN BIT SERIAL CODE -I
RESET~ , ~1~B~rr~O~~B~rr~I~~B~IT~2~~B~IT~3~I~B~IT~4~I~B~IT~5~1~B~rr_8~~B~IT_7~~B~IT~8~-2BI~T~9~1______
PO.2 UNDEFINED I
PO.! UNDEFINED I
Figura 5. Entry Into ProgramNerify Modes
February 1989 2-160

-n (/)
Q)
C" () cC·
s::
:::l
2 Q)
I»
-< g-
~
co
O III
1:
(J)
~ o·
(J) :g
::J a
(>
co Q)
!Z
CD Q
I
'tI
() aa.
12.75V ::::r c:
(>
PO.2 (Vpp) 5V / - - - - - - ".....::.;5V:...-_ _ _ _ _ _ __ "0 iii
P~LSES
CX)
I
H tSHGL 25 H tGHSL
OJ
;::;:
I I
L ___ JLJL~=rur------- s::
."
ii
PO.1 (PGM)
o·
~
!; 0
It
H tGLGH H tGHGL (")
!" r-tMASELl 0
'tI 98u5 MIN 1Qus MIN
I\)
~
I
.8ill
3
Po.o (ASEL) :::7 ,'-______________________________ ::J
.-+
~
0
0)
~
~ tHASETj' 'I' 'j tHAHLD CD

~
~
fJn PORT 3 ;>C HIGHADDRESS:><:~ ____~L~O~W~A~D~D~R~ES~S~_______________________________________________________________
CD
HtADSTA H t DVGL tGHDxj' 'I' t AvaV ---.I
PORT 1
INVALID DATA
... ,
VALID
...
DAT~
Ir--------------.:-....:.
DATA TO BE PROGRAMMED
... I
INVALID DATA
I VALID DATA
.. , , - - - - -
j. VERIFY MODE + PROGRAM MODE l' VERIFY MODE---i
'tI
ac:
(J) ~
CX) (/)
-...I "i(>
() ::;;
-...I o·
01 e
-L g"
8XC752 OVERVIEW Memory Organization
The 83C752 manipulates operands in three memory ad-

The Signetics 83C752/87C752 is a single-chip control
dress spaces. The first is the program memory space
oriented microcontroller fabricated with Signetics high-
which contains program instructions as well as constants
density CMOS technology minimizing CMOS latch-up
such as look-up tables. The program memory space con-
sensitivity. Being a member of the 80C51 family, the
tains 2Kbytes in the 83C752.
83C752 has a powerful instruction set, and has the same
basic architecture as the 80C5l. The 83C752 is essen-
The second memory space is the data memory array
tially the popular industry-standard 83C751 with the in-
which has a logical address space of 128 bytes. However,
clusion of a 5-channel multiplexed 8-bit ADC and a only the first 64 bytes (0 to 3FH) are implemented in
PWM output.
the 83C752.
The 83C752 contains a 2K X 8 masked ROM, 64 bytes
The third memory space is the special function register
of RAM, 21 110 lines, a 16-bit auto-reload timer/count-
array having a 128 byte address space (80H to FFH).
er, a fixed rate timer, a seven source fixed priority in-
Only selected locations in this memory space are used
terrupt structure, a bi-directional Inter-Integrated Cir-
(see Table 23). Note that the architecture of these
cuit (I2C) serial bus interface, and an on-chip oscillator.
memory spaces (internal program memory, internal data
This device also includes a 5-channel multiplexed 8-bit
memory, and special function registers) is identical to
AiD converter and an 8-bit PWM output.
the 80C51 and the 83C752 varies only in the amount of
The on-board 12C bus interface allows the 83C752 to op- memory physically implemented.
erate as a Master or Slave device on the 12C small area
The 83C752 does not directly address any external data
network. This capability facilitates 110 and RAM expan-
or program memory spaces. For this reason, the MOVX
sion, access to EEPROM, processor-to-processor com-
instructions in the 80C51 instruction set are not imple-
munications, and efficient interface to a wide variety of
mented in the 83C752, nor are the alternate I/O pin
dedicated 12C peripherals.
functions RD and WR.
The EPROM version of this device, the 87C752, is also
110 Ports
available in both quartz-lid erasable and plastic one-time
programmable (OTP) packages. Once the array has been The I/O pins provided by the 83752 consists of port 0,
programmed, it is functionally equivalent to the masked port 1, and port 3.
ROM 83C752. Thus, unless explicitly stated otherwise,
all references made to the 83C752 apply equally to the Port 0
87C752.
Port 0 is as-bit bi-directional I/O port and includes al-
The 83C752 supports two power reduction modes of op- ternate functions on some pins of this port. Pins PO.3
eration referred to as the idle mode and the power-down and PO.4 are provided with internal pullups while the
mode. remain.ing pins (PO.O, PO.1 and PO.2) have open drain
output structures. The alternate functions for port 0 are:
Idle Mode
PO.O SCL - the 12C bus clock
In the idle mode, the CPU puts .itself to sleep while all PO.1 SDA - the 12C bus data
of the on-chip peripherals stay active, except for the PO.4 PWM - the PWM output
AiD converter and the PWM output. The instruction
which places the 83C752 into the idle mode is the last If the alternate functions, 12C and PWM, are not being
instruction executed in normal operation before the idle used then these pins may be used as I/O ports.
mode is activated. The CPU contents, the on-chip RAM,
and all of the SFRs remain intact during this mode. The Port 1
idle mode can be terminated by any enabled interrupt or
by a hardware reset. An interrupt will cause processing Port 1 is an 8-bit bi-directional 110 port whose structure
to begin with the interrupt service routine. is identical to the 80C51, but also includes alternate in-
put functions on all pins. The alternate pin functions for
Power-Down Mode port 1 are:
In the power-down mode, the oscillator is stopped and Pl.0-Pl.4 - ADCO-ADC4 - AiD converter analog in-
the instruction to invoke power-down is the last instruc- puts
tion executed. Only the contents of the on-chip RAM is Pl.5 INTO - external interrupt 0 input
preserved. A hardware reset is the only way to terminate Pl.6 INT1 - external interrupt 1 input
the power-down mode. The control bits for the reduced Pl.7 - TO - timer 0 external input
power modes are in the PCON register.
February 1989 2-162


Table 23. 8XC752 Special Fuuction Registers

Address MSB LSB
ACC' Accumulator EOH E7 E6 E5 E4 E3 E2 EI EO OOH
ADAT# AID result 84H OOH
ADCON# AID control AOH - I - ENADC ADCI I ADCS LAADR21 AADRI AADRO COH
B" B Register FOH F7 F6 F5 F4 F3 F2 FI FO OOH
12CFG'# 12C configuration D8H/RD SLAVEN MASTRQ 0 TIRUN - - CTl CTO OOOOxxOOB
WR SLAVEN MASTRQ CLRTI~T1RUN~ - - CTl ~ CTO
9F 9E 9D 9C 9B 9A 99 98
I2CON"# 12C control 98H/RD RDAT ATN DRDY ARL STR STP MASTER - 81H
WR CXA IDLE CDR CARL CSTR CSTP XSTR XSTP
12DAT*# Pc data 99H/RD RDAT 0 0 0 0 0 0 0 80H
WR XDAT X X X X X X X
12STA"# I2C status F8H - IDLE XDATA XACTVJMAKSTRjMAKSTP XSTR XSTP xOlOOOOOB
IE"# Interrupt enable A8H EA EAD I ETI I ES I EPWM EXI ETO I EXO OOH
PooH Port 0 80H - - - 84 83 82 81 80 xxxlllllB
PI*# Port 1 90H 97 96 95 94 93 92 91 90 FFH
P3"# Port 3 BOH B7 B6 B5 B4 B3 B2 BI BO FFH
PCON# Power control 87H - - I - I - - - PD ~ IDL xxxxOOOOB
D7 D6 D5 D4 D3 D2 DI DO
PSW* Program status word DOH CY AC I FO _L RSI RSO OV - P OOH
PWCM# PWM compare 8EH xxxxxxxxB
PWENA# PWM enable FEH -
PWMP# PWM prescaler 8FH
- - I I - - - - PWE FEH
OOH
RTL# Timer low reload 8BH OOH
RTH# Timer high reload 8DH DOH
TL# Timer low 8AH DOH
TH# Timer high 8CH OOH

TCON"# Timer control 88H 8F 8E 8D 8C 8B 8A 89 88 OOH
GATE I CIT TF TR I lEO I ITO I IEI ITI OOH
• = SFRs are bIt addressable.
If the alternate functions INTO, INTI, or TO are not The 8-bit counter counts from 0 to 254 inclusive. The
being used, these pins may be used as standard I/O value of the 8-bit counter is compared to the contents of
ports. If the ND converter is not enabled, pins the compare register, PWM. When the content's value
Pl.O- Pl.4 can be used as standard I/O pins. matches that of the PWM register, the PWM output is
set high. When the counter reaches zero, the PWM out-
Port 3 put is set low. The pulse width ratio (duty cycle) is de-
fined by the contents of the compare register and is in
Port 3 is an 8-bit bi-directional I/O port whose structure the range of 0 to I programmed in increments of 11255.
is identical to the 80C5l. Note that the alternate func-
tions associated with port 3 of the 80C51 have been The PWM output can be set continuously high by loading
moved to port I of the 83C752 (as applicable). See Fig- the compare register with OOH and continuously low by
ure 63 for port bit configurations. loading the compare register with FFH. The PWM out-
put is enabled by setting the PWE bit in the PWM en-
PWM Outputs able register, PWENA. When enabled, the output is
driven with a fully active strong pullup. When disabled,
The single PWM output is an alternate function assigned the pin behaves as a normal bi-directional I/O pin.
to PO.4, and can be used to output pulses of program- When disabled, the counter remains active. The PWM
mable length and interval. The repetition frequency is function is disabled by a reset condition. The PWM out-
defined by an 8-bit prescaler which generates the clock put is high during power-down and idle modes and the
for the counter. This prescaler is contained in the counter is disabled.
PWMP register.
February 1989 2-163

AID Converter
ALTERNATE
OUTPUT
The 83C752 contains a 5-channel multiplexed 8-bit ND
READ converter. The conversion requires 40 machine cycles
LATCH VDD (40).lS at 12MHz oscillator frequency).
INTERNAL
-I PULL·UP
The ND converter is controlled by the ND control reg-
INT BUS ister, AD CON. Input channels are selected by the analog
multiplexer by bits ADCON.O through ADCON.2. TI,e
ADCON register is not bit addressable.
WRITE TO
LATCH ADCON Register
MSB Lsn
READ PIN
x I x
ALTERNATE ADCI ADCS Operation
INPUT
a a ADC not busy, a conversion can be started.
FUNCTION a I ADC busy, start of a new conversion is
blocked.
o Conversion completed, start of a new conver-
ALTERNATE sion is blocked.
OUTPUT Not possible.
READ FUNCTION
Input Channel Selection
LATCH
ADDR2 ADDRI ADDRa Input Pin
0 0 0 PI.O
0 0 I Pl.l
INT BUS 0 I 0 PI.2
0 I I PI.3
1 0 a PI.4
WRITE TO
LATCH Position Symbol Function
ADCON.5 ENADC Enable AID function when ENADC - L
Disable AID function when ENADC - a.
Reset forces ENADC - O.
READ PIN ADCON.4 ADCI ADC interrupt flag. This flag is set when
ALTERNATE
an ADC conversion is complete. If IE.6 >=
INPUT 1, an interrupt is requested when ADCI -
FUNCTION
1. The ADCI flag is cleared when con-
version data is read. This nag is read only.
ADCON.3 ADCS ADC start and status. Setting this bit starts
an ND conversion. Once set, ADCS
Figure 63. Port Bit Latches and 1/0 Buffers remains high throughout the conversion
cycle. On completion of the conversion, it
is reset at the same time the ADCI
The repetition frequency is given by: interrupt flag is set. ADCS cannot be reset
by software.
ADCON.2 AADR2 Analog input select.
fose ADCON.l AADRI Analog input select.
fpWM ~ -------- ADCON.O AADRO Analog input select. This binary coded
2 x (1 + PWMP) 255 address selects one of the five analog
input port pins of PI to be input to the
An oscillator frequency of 12MHz results in a repetition converter. It can only be changed when
ADCI and ADCS are both low. AADR2 is
range of 92Hz to 23.5KHz. the most significant bit.
The low/high ratio of the PWM output is PWM / (255

The completion of the 8-bit ADC conversion is flagged
PWM) for PWM values except 255. A PWM value of
by ADCI in the ADCON register and the result is stored
255 results in the low PWM output.
in the special function register ADAT.
If enabled, a PWM interrupt will occur when the PWM
An ADC conversion in progress is unaffected by an ADC
counter overflows.
start. "D,e result of a completed conversion remains un-
In order for the PWM output to be used as a standard affected provided ADCI remains at a logic 1. While
I/O pin, the PWM function needs to be disabled. The ADCS is a logic 1 or ADCI is a logic 1, a new ADC
PWM counter can still be used as an internal timer by START will be blocked and consequently lost. An ADC
enabling the PWM interrupt.
February 1989 2-164

conversion in progress is aborted when the Idle or timer/counter is enabled. Register pair TH and TL are
Power-down mode is entered. The result of a completed incremented by the clock source. When the register pair
conversion (ADCI ~ logic 1) remains unaffected when overflows, the register pair is reloaded with the values in
entering the Idle mode. See Figure 64 for an ND input registers RTH and RTL. The value in the reload regis-
equivalent circuit. ters is left unchanged. The TF bit in special function
register TCON is set on counter overflow and, if the in-
The analog input pins ADCO-ADC4 may be used as dig- terrupt is enabled, will generate an interrupt (see Figure
ital inputs and outputs when the A/D converter is dis- 65).
abled by a 0 in the ENADC bit in ADCON. When the
ND is enabled, the analog input channel that is selected 12C Serial 110
by the ADDR2-ADDRO bits in ADCON cannot be used
as a digital input. Reading the selected ND channel as The I2C bus uses two wires (SDA and SCL) to transfer
a digital input will always return a 1. The unselected information between devices connected to the bus. The
ND inputs may always be used as digital inputs. main technical features of the bus are:
CounterlTimer • Bidirectional data transfer between masters and slaves

• Serial addressing of slaves
The 8XC752 counter/timer is designated Timer 0 and is • Acknowledgment after each transferred byte
separate from Timer I of the 12C serial port and from • Multimaster bus
the PWM. Its operation is similar to mode 2 of the • Arbitration between simultaneously transmitting master
80C51 counterltimer, extended to 16 bits. When Timer without corruption of serial data on bus
o is used in the external counter mode, the TO input
(P1.7) is sampled every S4Pl. The counter/timer func- A large family of 12C compatible ICs is available. See
tion is controlled using the timer control register the 12C section for more details on the bus and available
(TCON) ICs.
TCON Register The 83C752 I2C subsystem includes hardware to simplifY

the software required to drive the I2C bus. This circuitry
MSB LSB is the same as that on the 83C751. (See the 83C751 sec-
IGATEI CIT I TF TR lEO ITO 1E1 IT1 tion for a detailed discussion of this subsystem).
Position Symbol Function
TCON.7 GATE 1 - Timer 0 is enabled only when INTO pin is Interrupts
high and TR is 1
o - Timer 0 is enabled only when TR is 1 The interrupt structure is a seven source, one level in-
TCON.6 CIT 1 - Counter operation from TO pin terrupt system similar to the 8XC751. The interrupt
o - Timer operation from internal clock sources are listed below in their order of polling se-
TCON.5 TF 1 - Set on overflow of TO
o - Cleared when processor vectors to inter- quence priority (highest to lowest):
rupt routine and by reset
TCON.4 TR 1 - Enable timer 0
o - Disable timer 0 Priority Source Function
TCON.3 lEO 1 - Edge detected on INTO Highest INTO External interrupt 0
TCON.2 ITO 1 - INTO is edge triggered TFO Timer flag 0
o - INTO is level sensitive INTl External interrupt 1
TCON.l lEi 1 - Edge detected on INTi PWM PWM counter overflow
TCON.O ITl 1 - INTl is edge triggered TI l2C timer overflow
o - INTi is level sensitive SIO Serial port interrupt
These flags are functionally identical to the corre- Lowest ADC A/D conversion complete
sponding 80C51 flags except that there is only one of the
80C51 style timers and the flags are combined into one The vector addresses are as follows:
register.
Vector
A communications watchdog timer Timer I, is described Source Address
INTO 0003H
in the 12C section. In I2C applications, this timer is ded-
TFO OOOBH
icated to time generation and bus monitoring for the INTl 0013H
12C. In non-I2C applications, it is available for use as a TIMER I 00lBH
fixed time base. SIO 0023H
ADC 002BH
The 16-bit timer/counter's operation is similar to mode PWM 0033H
2 operation on the 80C51, but is extended to 16 bits. Interrupt Control Registers
The timer/counter is clocked by either 1/12 the oscilla-
tor frequency or by transitions on the TO pin. The CIT The 80C51 interrupt enable register is modified to take
pin in special function register TCON selects between into account the different interrupt sources of the
these two modes. When the TCON TR bit is set, the 8XC752.
February 1989 2-165

.-- ·-----·----~-------·1
•
••
I~,
S;~, R~~,
~
II
-j---1"- --U'V\,'\r"-~-t
Sm. Rm.
I. TO COMPARATOR
WV\r-+--I--------------
+ MULTIPLEXER
c.
~NAlOGINPUT
Rm - O.S-3Kohms
Cs + Cc - 1SpF maximum
Rs - Recommended < 9.6Kohms for 1 LSB @ 12MHz
NOTE:
Because the analog to digital converter has a sampled-data comparator, the input looks capacitive to a source. When a
conversion is initiated, switch Sm closes for 8tcy (8JlS @ 12MHz crystal frequency) during which time capacitance Cs + Cc
is charged. It should be noted that the sampling causes the analog input to present a varying load to an analog source.
Figure 64. Am Input: Equivalent Circuit
Interrupt Enable Register ing Timer I, the counter portion of the PWM, and the
interrupts. Upon powering-up the circuit, or exitiug from
MSB LSB
idle mode, sufficient time must be allowed for stabiliza-
I EA IEAD I ETI I ES IEPWM I EXI I ETO I EXO I tion of the internal analog reference voltages before an
ND conversion is started.
Position Symbol Function
1E.7 EA Global interrupt disable when EA = 0 Instruction Set
1E.6 EAD ND conversion complete
IE.S ETI Timer I The instruction set of the 83C7S2 is identical to the
1E.4 ES 12C serial port 80CSI except that:
1E.3 EPWM PWM counter overflow
1E2 EXI External interrupt I MOVX, LCALL and UUMP are not implemented.
IE.I ETO Timer 0 overflow
IE.O If these instructions are executed, the appropriate
EXO External interrupt 0
number of instruction cycles will take place along with
Power-Down and Idle Modes external fetches, however, no operation will take place.
The UMP may not respond to all program address bits.
The 8XC752 includes the 80C51 power-down and idle
mode features. The functions that continue to run while
in the idle mode are Timer 0, the 12C interface includ-
February 1989 2-166

osc 112
TF INT
TO PIN - - - - - - - - - - - '
TR
GATE
INTO PIN
RTL RTH
Figure 65. 83C752 CounterrI'imer Block Diagram
The special function registers (directly addressable only)

contain all of the 8XC751 registers except the program
counter and the four register banks. Most of the 21 spe-
cial function registers are used to control the on-chip
peripheral hardware. Other registers include arithmetic
registers (ACC, E, PSW), stack pointer (SP) and data
pointer registers (DPH, DPL). Nine of the SFRs are bit
addressable.
Data Pointer
The Data Pointer DPTR) consists of a high byte (DPH)
and a low byte (D PL). In the 80C51, this register allows
the access of external data memory using the MOVX
instruction.
Ports 0, 1, 2
PO, P1, P2 are the latches of Ports 0, 1, and 2, respec-

tively. P1 and P2 are each 8 bits wide while PO has only
five valid bits since it represents a 5-bit port.
February 1989 2-167

Signetics S87C752
Microcontroller
Preliminary Specification

The Signetics S87C752 offers many of • EPROM version of S83C752
the advantages of the SC80C51 archi- • Available in erasable quartz lid
tecture in a small package and at low or One-Time Programmable P3.4/A4 1
cost. plastic packages
The S87C752 Microcontroller is fabri- • Inter-Integrated Circuit (12C)
cated with Signetics high-density CMOS serial bus interface
technology. Signetics epitaxial substrate • Small package sizes
minimizes CMOS latch-up sensitivity. - 28-pin DIP
The S87C752 contains a 2K x 8 E- - 28-pin PlCC
PROM, a 64 x 8 RAM, 21 I/O lines, a
16-bit auto-reload counter/timer, a fixed- • low power consumption:
rate timer, a seven-5ource fixed-priority
- Normal operation: less
interrupt structure, a bidirectional Inter-
- Idle mode
Integrated Circuit (12C) serial bus inter-
- Power-down mode
face, an on-chip oscillator, a five chan-
• 2K x 8 EPROM, 64 x 8 RAM
nel multiplexed 8-bit A/D converter, and
• 16-bit auto reloadable counter!
an 8-bit PWM output.
timer
The onboard inter-integrated circuit (12C) • 5 channel 8-bit AID converter
bus interface allows the S87C752 to op- • 8-bit PWM output/timer
erate as a master or slave device on the • Fixed-rate timer
12C small area network. This capability
facilitates I/O and RAM expansion, ac- TOP VIEW
• Well suited for logic replace-
cess to EEPROM, processor-to-proces-
ment, consumer and industrial INDEX
face to a wide variety of dedicated 12C
peripherals.
applications
lOGIC SYMBOL
,om! ,,~ ~['"
11 19
12 18
TOP VIEW

1 P3.4/A4 15 P1.21 ADC2/D2
2 P3.3/A3 16 P1.31 ADC3/D3
3 P3.2/A2/A10 17 P1.41 ADC4/D4
4 P3.1/A1/A9 18 AVss
5 P3.01 AOI A8 19 AVec
6 PO.2iVpp 20 P1.5iiNi'ii/D5
7 PO.1/SDAI 21 p1.6iiFJ'fi ID6
OE-PGM 22 P1.7/TO/D7
PO.O/SCLI 23 PO.3
ASEL 24 PO.4/PWM
9 RST OUT
10 X2 25 P3.7/A7
11 X1 26 P3.6/A6
12 Vss 27 P3.5/A5
13 P1.0/ADCO/DO 28 Vee
14 P1.1/ADC1/D1
NOTE:
AO-Al0 and 00-07 available for EPROM
verify only.
February 1989 2-168

Signetics Microprocessor Products Preliminary Specification

S87C752- c Part Number Speed Temperature and Package
L,~.".~."
S87C752 1F28 3.5 to 12MHz o to +70°C, Ceramic DIP
S87C752-3F28 0.5 to 12MHz o to +70°C, Ceramic DIP
S87C752-4F28 3.5 to 16MHz o to +70°C, Ceramic DIP
A28 - Plastic PLCC (OTP)
S87C752-1 N28 3.5 to 12MHz o to +70°C, Plastic DIP
F28 - Ceramic DIP S87C752-2N28 3.5 to 12MHz . -40 to +85°C, Plastic DIP
N28 - Plastic DIP (OTP)
Speed and Temperature Range:
S87C752-3N28 0.5 to 12MHz o to +70°C, Plastic DIP
1- 3.5 to 12MHz, OoC to +70°C S87C752-4N28 3.5 to 16MHz o to +70°C, Plastic DIP
2- 3.5 to 12MHz, _40°C to +85 °c S87C752-5N28 3.5 to 16MHz -40 to +85°C, Plastic DIP
3- 0.5 to 12MHz, OOC to +70° C
4- 3.5 to 16MHz, OOC to +70° C S87C752 1A28 3.5 to 12MHz o to +70°C, Plastic LCC
5- 3.5 to 16MHz, -40°C to +85 °c
S87C752-2A28 3.5 to 12MHz -40 to +85°C, Plastic LCC
S87C752-3A28 0.5 to 12MHz o to +70°C, Plastic LCC
S87C752-4A28 3.5 to 16MHz o to +70°C, Plastic LCC
S87C752 5A28 3.5 to 16MHz -40 to +85°C, Plastic LCC
BLOCK DIAGRAM
----------~~ ----------l
L _____ J
February 1989 2-169

PIN CONFIGURATION (DIP and PLCC)
MNEMONIC PIN NO. TYPE NAME AND FUNCTION

Vss 12 Circuit ground potential.
Vee 28 Supply voltage during normal, idle, and power-down operation.
PO.0-PO.4 8-6, 110 Port 0: Port 0 is a 5-bit bidirectional port. Port 0.0 - PO.2 are open drain. Port 0.0 - PO.2 pins
23, 24 that have ones written to them float, and in that state can be used as high-impedance inputs.
PO.3-P004 are bi-directional 110 port pins with internal pullups. Port 0 also serves as the serial
12C interface as shown in the pinout diagram. When this feature is activated by software, SCL and
SDA are driven low in accordance with the 12C protocol. These pins are driven low if the port
register bit is written with a 0 or if the 12C subsystem presents a O. The state of the pin can
always be read from the port register by the program. Port 0.3 and 004 have internal pull-ups that
function identically to port 3. Pins that have ones written to them are pulled high by the internal
pull-ups and can be used as inputs.
To comply with the 12Cspecification, PO.O and PO.1 are open drain bidirectional 110 pins with the
electrical characteristics listed in the tables that follow. While these differ from 'standard TTL'
characteristics, they are close enough for the pins to still be used as general-purpose 110 in
non-12C applications.
7 110 SDA (PO.1) 12C data.
8 110 SCl (PO.O) 12C clock.
24 0 PWM OUT (PO.4) - This pin also functions as the pulse width modulated output. When the PWM
is enabled, the output (PO A) has a strong active pull-up and cannot be used as an input. (see DC
Electrical Characteristics).
Port 0 also provides alternate functions for programming the EPROM memory as follows:
6 I Vpp (PO.2) - Programming voltage input.
7 I OE/PGM (PO. 1) - Input, OE/PGM, which specifies verify mode (output enable) or the prrogram
mode.
OE/PGM - 1 output enabled (verify mode)
OE/PGM - 0 program mode.
8 I ASEl (PO,O) - input which indicates which bits of the EPROM address are applied to port 3.
ASEL - 0 low address byte available on port 3.
ASEL - 1 high address byte is available on port 3 (only the three least significant bits are used).
P1.0-P1.7 13-17, 110 Port 1: Port 1 is an 8-bit bidirectional 110 port with internal pullups. Port 1 pins that have ones
20-22 written to them are pulled high by the internal pull ups and can be used as inputs. PO.3-P004 pins
are bi-directional 110 port pins with internal pull ups. As inputs, port 1 pins that are externally
pulled low will source current because of the internal pullups. (See DC electrical characteristics:
. IILl· Port 1 also serves the special function features of the SC80C51 family as listed below:
20 INTO (Pl.5): External interrupt
21 INTl (Pl.6): External interrupt
22 TO (Pl.7): Timer 0 external input
13-17 I ADCO (Pl.0) - ADC4 (Pl.4) - Port 1 also functions as the inputs to the five channel multiplexed
AID converter. These pins can be used as outputs only if the AID function has been disabled.
These pins may be used as inputs while the AID converter is enabled.
Port 1 serves to output the addressed EPROM contents in the verify mode and accepts as inputs
the value to program into the selected address during the program mode.
P3.0-P3.7 5-1 110 Port 3: Port 3 is an 8-bit bidirectional I/O port with internal pullups. Port 3 pins that have ones
27-25 written to them are pulled high by the internal pullups and can be used as inputs. As inputs, port
3 pins that are externally being pulled low will source current because of the pull ups (See DC
electrical characteristics: IILl. Port 3 also functions as the address input for the EPROM memory
location to be programmed (or verified). The 11-bit address is multiplexed into this port as spec-
ified by PO.O/ASEL.
RST 9 I Reset: A high on this pin for two machine cycles while the oscillator is running resets the device.
An internal diffused resistor to VSS permits a power-on RESET using only an external capacitor
to Vee. After the device is reset, a 10-bit serial sequence., sent LSB first, applied to RESET,
places the device in the programming state allowing programming address, data and Vpp to be
applied for programming or verification purposes. The RESET serial sequence must be synchro-
nized with the X1 input.
X1 11 I Crystal 1: Input to the inverting oscillator amplifier and input to the internal clock generator
circuits. X1 also serves as the clock to strobe in a serial bit stream into RESET to place the de-
vice in the programming state.
X2 10 o Crystal 2: Output from the inverting oscillator amplifier.
AVcc 19 I Analog supply voltage and reference input.
AVss 18 I Analog supply and reference ground.
February 1989 2-170


OSCILLATOR CHARACTERISTICS Program Memory tents of a compare register, PWM. When
X1 and X2 are the input and output, re- Event Address the counter value matches the contents
spectively, of an inverting amplifier Reset 000 of this register, the output of PWM is set
which can be configured for use as an External INTO 003 high. When the counter reaches zero,
on-<:hip oscillator. Counter/timer 0 OOB the output of PWM is set low. The pulse
External I NT1 013 width ratio (duty cycle) is defined by the
To drive the device from an external Timer I 01B contents of the compare register and is
clock source, X1 should be driven while 12C serial 023 in the range of 0 to 1 programmed in
X2 is left unconnected. There are no re- ADC 02B increments of 1/255. The PWM output
quirements on the duty cycle of the ex- PWM 033 can be set to be continuously high by
ternal clock signal, because the input to loading the compare register with a and
the internal clock circuitry is through a Counter/Timer Subsystem the output can be set to be continuously
divide-by-two flip-flop. However, mini- The S87C752 has one counter/timer
low by loading the compare register with
mum and maximum high and low times called timer/counter O. Its operation is 255. The PWM output is enabled by a bit
specified in the data sheet must be similar to mode 2 operation on the
in a special function register, PWENA.
observed. SC80C51, but is extended to 16 bits with
When enabled, the pin output is driven
16 bits of autoload. The controls for this with a fully active pull-up. That is, when
IDLE MODE counter are centralized in a single regis-
In the idle mode, the CPU puts itself to the output is high, a strong pull-up is
ter called TCON.
sleep while all of the on-<:hip peripherals continuously applied. When disabled, the
stay active, except for the A/D con- A watchdog timer, called Timer I, is for pin behaves as a normal bidirectional I/O
verter and the PWM output. The instruc- pin, however, the counter remains
use with the 12C subsystem. In 12C appli-
tion to invoke the idle mode is the last active.
cations, this timer is dedicated to time-
instruction executed in the normal oper- generation and bus monitoring of the The PWM function is disable during RE-
ating mode before the idle mode is acti- 12C. In non-12C applications, it is avail- S ET and remains disabled after reset is
vated. The CPU contents, the on-<:hip able for use as a fixed timebase. removed until re-Bnabled by software.
RAM, and all of the special function reg-
The PWM output is high during power
isters remain intact during this mode. The Interrupt Subsystem - Fixed Priority
down and idle. The counter is disabled
idle mode can be terminated either by The I P register ,and the 2-level interrupt
during idle. The repetition frequency of
any enabled interrupt (at which time the system of the SC80C51 are eliminated.
the PWM is given by:
process is picked up at the interrupt Simultaneous interrupt conditions are re-
service routine and continued), or by a solved by a single-level, fixed priority as fpWM - fose /2 (1 + PWMP) 255
hardware reset which starts the proces- follows:
sor in the same manner as a power-on The low/high ratio of the PWM signal is
reset. Highest priority: Pin INTO PWM / (255 - PWM) for PWM not equal
Counter/timer flag 0 to 255. For PWM - 255, the output is
POWER-DOWN MODE Pin INn always low.
In the power-<lown mode, the oscillator PWM
is stopped and the instruction to invoke Timer I The repetition frequency range is 92H z
power-<lown is the last instruction exe- Serial 12C to 23.5kHz for an oscillator frequency of
cuted. Only the contents of the on-<:hip Lowest priority: ADC 12MHz.
RAM are preserved. A hardware reset is
the only way to terminate the power- Serial Communications An interrupt will be asserted upon PWM
down mode. The control bits for the re- The S87C752 contains an 12C serial com- counter overflow if the interrupt is not
duced power modes are in the special munications port instead of the SC80C51 masked off.
function register PCON. UART. The 12C serial port is a single bit
hardware interface with all of the hard- The PWM output is an alternative func-
Table 1. External Pin Status During ware necessary to support multimaster tion of PO.4. In order to use this port as
Idle and Power-Down Modes and slave operations. Also included are a bidirectional I/O port, the PWM output
receiver digital filters and timer (timer I) must be disabled by clearing the en-
Mode Port O· Port1 Port 2
for communication watch-<log purposes. able/disable bit in PWENA. In this case,
Idle Data Data Data The 12C serial port is controlled through the PWM subsystem can be used as an
Power-down Data Data Data four special function registers; 12C con- interval timer by enabling the PWM
.Except for PWM output (PO.4) trol, 12C data, 12C status, and 12C config-
interrupt.
uration. AID Converter
DIFFERENCES BETWEEN THE The analog input circuitry consists of a
S87C752 AND THE SC80C51 Pulse Width Modulation Output (PO.4) 5-input analog multiplexer and an A to D
The PWM outputs pulses of program-
converter with 8-bit resolution. The con-
Program Memory mable length and interval. The repetition
On the S87C752, program memory is version takes 40 machine cycles, i.e.,
frequency is defined by an 8-bit
2048 bytes long and is not externally prescaler which generates the clock for 40JlS at 12MHz oscillator frequency. The
expandable. Program memory can con- A/D converter is controlled using the
the counter. The prescaler register is
tain S87C752 instructions and constant PWMP. The prescaler and counter are ADCON control register. Input channels
data. The only fixed locations in program not associated with any other timer. The are selected by the analog multiplexer
memory are the addresses at which exe- through ADCON register bits 0-2.
8-bit counter counts modulo 255, that is
cution is taken up in response to reset from 0 to 254 inclusive. The value of the
and to interrupts, which are as follows: 8-bit counter is compared to the con-
February 1989 2-171

Special Function Register Addresses SCSOC51 special function registers not RTH, RTL, 12CON, and 120AT, respec-
Special function register addresses for present in the SS7C752 are TMOO (S9), tively. Additional special function regis-
the SS7C752 are identical to those of P2 (AO) and IP (B8). The SCSOC51 registers are 12CFG (OS), 12STA (FB),
the SC80C51, except for the changes ters TH1, TL1, SCON, and SBUF are AOCON (AO) , AOAT (S4), PWM (SE),
listed below: replaced with the SS7C752 registers PWMP (SF), and PWENA (FE).
Table 2. 12<: Special Function Register Addresses

12C control 12CON 9S 9F 9E 90 9C 9B 9A 99 9S
12C data 120AT 99 - - - - - - - -
12C configuration 12CFG OS OF OE 00 OC OB OA 09 OS
12C status 12STA FS FF FE FD FC FB FA F9 FS

Vee Voltage from Vee to VSS 3 -0.5 to +6.5 V
Vs Voltage from any pin to VSS 3 -0.5 to Vee + 0.5 V
DC ELECTRICAL CHARACTERISTICS TA = O°C to +70°C or TA - -40°C to +S5°C, AVec - 5V ±10%, AVss - OV3
LIMITS
Min Max
Icc Supply current (see Figure 3) TBO
Inputs
VIL Input low voltage, except.SOA, SCL -0.5 0.2Vee-0.1 V
VIH Input high voltage, except Xl, RST 0.2Vee+0.9 Vee+0.5 V
VIHI Input high voltage, X1, RST 0. 7Vee Vee+0 .5 V
SOA, SCl:
VIL1 Input low voltage -0.5 0. 3Vee V
VIH2 I nput high voltage O· 7Vee Vee+0.5 V
OutDuts
VOL Output low voltage, ports 1, 3, 0.3, and 0.4 (PWM disabled) IOL - 1.6mA 0.45 V
VOLl Output low voltage, port 0.2 IOL - 3.2mA 0.45 V
VOH Output high voltage,ports 1, 3, 0.3, and 0.4 (PWM disabled) IOH - -60)lA 2.4 V
IOH - -25)lA 0.75Vee V
IOH = -10)lA 0. 9Vee V
VOH2 Output high voltage, PO.4 (PWM enabled) IOH - -400)lA 2.4 V
IOH - -40)lA 0.9Vee V
Port 0.0 and 0.1 (12C) - Orivers
VOL2 Output low voltage 0.4 V
IOL - 3mA
(over Vee range)
Driver, receiver combined:
C Capacitance 10 pF
IlL logical 0 input current, ports 1, 3, 0.3, and 0.4 (PWM disabled) VIN - 0.45V -50 )lA
ITL logical 1 to 0 transition current, ports 1, 3, 0.3 and 0.4 VIN - 2V -650 )lA
III Input leakage current, port 0.0, 0.1 and 0.2 0.45 < VIN < Vee ±10 )lA
CIO Pin capacitance Test freq - 1 MHz, 10 pF
TA - 25°C
Ipo Power-down current6 Vee - 2 to 5.5V 50 )lA
Vpp Vpp program voltage VSS - OV 12.5 13.0 V
Vee - 5V±10%
TA - 21°C-27°C
Ipp Program current Vpp - 13.0V 10 rnA
February 1989 2-172

TEST LIMITS
CONDITIONS Min Typical Max
Analog Inputs (AID guaranteed only with quartz window covered.)
AVcc Analog supply voltage 9 AVcc - Vcc±O·2 4.5 5.5 V
Analog supply current
Aicc Operating TBD mA
AIID AVcc - 5.12V
Idle modeS TBD mA
AI PO TBD mA
Power-downS
AVIN Analog input voltage AVss-O.2 AVcc+O.2 V
CIA Analog input capacitance TBD pF
tAOS Sampling time StCY s
tADC Conversion time 40tCY s
R Resolution S bits
ERA Relative accuracyS ±1 LSB
OSe Zero scale offsetS TBD LSB
Ge Full scale gain errorS TBD %
MCTC Channel to channel matching TBD LSB
Ct Crosstalk 0- 100kHz TBD dB
NOTES:
functional operation of the device at these or any other conditions than those described in the AC and DC Electrical Characteristics
4. Power-down ICC is measured with all output pins disconnected; port 0 - Vee; X2, X1 n.c.; RST - Vss.
5. Icc is measured with all output pins disconnected; Xl driven with tClCH, tCHCl - 5ns, Vil - Vss + O.5V, VIH = Vcc - O.5V; X2 n.c.; RST -
port 0 - Vcc. ICC will be slightly higher il a crystal oscillator is used.
6. Idle Icc is measured with all output pins disconnected; Xl driven with tClCH, tCHCl - 5ns. Vil - VSS + O.5V, VIH - Vcc - O.5V; X2 n.c.;
port 0 - VCC; RST - VSS.
7. load capacitance lor ports - SOpF.
8. The resistor ladder network is not disconnected in the power down or idle modes. Thus, to conserve power, the user may remove AVec.
9. II the AID lunction is not required, or il the AID lunction is only needed periodically. AVCC may be removed without affecting the
operation 01 the digital circuitry. Contents 01 ADCON and ADAT are not guaranteed to be valid. Digital inputs on P1.0-P1.4 will not
lunction normally.
AID CONVERTER PARAMETER Nonlinearity sometimes be referred to as full scale

DEFINITIONS 11 a straight line is drawn between the error.
The following list of definitions are in- end points of the actual converter char-
cluded to clarify the speCifications given. acteristic such that zero offset and full Offset Error
These definitions are not meant to be a scale errors are removed, then non- Offset error is the difference between
complete set of AID parameter defini- linearity is the maximum deviation of the the actual input voltage that causes the
tions. code transitions of the actual character- first code transition and the ideal value
istic from that of the straight line so con- to cause the first code transition. This
Absolute Accuracy Error structed. This is also referred to as rela- ideal value is 1/2 LSB above Vral-.
Absolute accuracy error at a given out-
tive accuracy and also integral non-
put is the difference between the theo- Channel to Channel Matching
linearity.
retical analog input voltage to produce a Channel to channel matching is the
given output code and the actual analog Differential Nonlinearity maximum difference between the corre-
input voltage required to produce the Differential nonlinearity is the maximum sponding code transitions of the actual
same code. Since the same output code difference between the actual and ideal characteristics taken from different
is produced by a band of input voltages, code widths of the converter. The code channels under the same temperature,
the "required input voltage" is defined as widths are the differences expressed in voltage and frequency conditions.
the midpoint of the band of input volt- LSB between the code transition points,
ages that will produce that code. Abso- as the input voltage is varied through the Crosstalk
lute accuracy error not specified with a Crosstalk is the measured level of a sig-
range for the complete set of codes.
code is the maximum over all codes. nal at the output of the converter re-
Gain Error sulting from a signal applied to one
Absolute accuracy error includes gain er- Gain error is the deviation between the deselected channel.
ror, offset error and relative accuracy ideal and actual analog input voltage re-
error, and accounts for all deviations quired to cause the final code transition
from an ideal converter. to a full-scale output code after the off-
set error has been removed. This may
February 1989 2-173

Sigl)etics Microprocessor Products Preliminary Specification
Total Error Relative Accuracy

Maximum deviation of any step point Relative accuracy error is the deviation
from a line connecting the ideal first of the ADC's actual code transition
transition point to the ideal last transition points from the ideal code transition
point. points on a straight line which connects
the ideal first code transition point and
the final code transition point, after
nulling offset error and gain error. It is
generally expressed in LSBs or in per-
cent of FSR.
AC ELECTRICAL CHARACTERISTICS TA - DoC to +70°C or TA - -40°C to +85°C, VCC - 5V±10%, Vss - OV3, 7

Min Max Min Max
3.5 12
l/tCLCL Oscillator frequency 3.5 16 MHz
0.5 12

tClCH Rise time 20 ns
AC SYMBOL DESIGNATIONS
Each timing symbol has five characters. The first character is H - Logic level high
always 't' (- time). The other characters, depending on their L - Logic level low
positions, indicate the name of a signal or the logical status of Q - Output data
that Signal. The designations are: T - Time
C - Clock V - Valid
D - I nput data X - No longer a valid logic level
Z - Float
vcc~.I1
~CI.2\t:c+Q.8
CI.2 \t:c _0.1
IIAIIV
DMV
V
D.2 \t:c +D.8
__________-J~~._~Q.:2~\t:c~-O'~I----------------.
X ,.__~---------
February 1989 2-174

22 MAX ACTIVE lee 5
20
/
V
18
16
/
14
/
t
..: 12
/ TYP ACTIVE lee 5
E
.2 10
/ /"
8
/'
/'
6 /'
V
4
2
/'
4
-- 8
FREQ - MHz
12
l---- MAX IDLE lee 6
TYP IDLE lee 6
16

Maximum Icc values taken at Vcc and Worst Case Temperature
Typical IcC values taken at Vcc = 5V and 25°C
Notes 5 and 6 refer to AC Electrical Characteristics
February 1989 2-175

PROGRAMMING CONSIDERATIONS these pins function as normal quasi- Encryption Key Table
bidirectional I/O ports and the program- The 87C752 includes a 16 byte EPROM
EPROM Characteristics ming equipment may pull these lines low. array that is programmable by the end
The 87C752 is programmed by using a However, prior to sending the 10 bit user. The contents of this array can then
modified Quick-Pulse Programming algo- code on the reset pin, the programming be used to encrypt the program memory
rithm similar to that used for devices equipment should drive these pins high contents during a program memory verify
such as the 87C451 and 87C51. It differs (V,H). The RESET pin may now be used operation. When a program memory ver-
from these devices in that a serial data as the serial data input for the data ify operation is performed, the contents
stream is used to place the 87C752 in stream which places the 87C752 in the of the program memory location is
the programming mode. programming mode. Data bits are XNOR'ed with one of the bytes in the 16
sampled during the clock high time and byte encryption table. The resulting data
Figure 4 shows a block diagram of the
thus should only change during the time pattern is then provided to port 1 as the
programming configuration for the
that the clock is low. Following transmis- verify data. The encryption mechanism
87C752. Port pin PO.2 is used as the
sion of the last data bit, the RES ET pin can be disabled, in essence, by leaving
programming voltage supply input (Vpp
should be held low. the bytes in the encryption table in their
signal). Port pin PO.1 is used as the pro-
erased state (FFH) since the XNOR
gram (PGM!) signal. This pin is used for Next the address information for the lo- product of a bit with a logical one will
the 25 programming pulses. cation to be programmed is placed on result in the original bit. The encryption
port 3 and ASEL used to perform the bytes are mapped with the code memory
Port 3 is used as the address input for
address multiplexing, as previously de- in 16 byte groups. The first byte in code
the byte to be programmed and accepts
scribed. At this time, port 1 functions as memory will be encrypted with the first
both the high and low components of the
an output. byte in the encryption table; the second
eleven bit address. Multiplexing of these
address components is performed using byte in code memory will be encrypted
A high voltage Vpp level is then applied with the second byte in the encryption
the AS EL input. The user should drive to the Vpp input (PO.2). (This sets Port 1
the ASEL input high and then drive port table and so forth up to and including
as an input port.). The data to be pro- the sixteenth byte. The encryption re-
3 with the high order bits of the address. grammed into the EPROM array is then
ASEL should remain high for at least 13 peats in 16 byte groups; the seventeenth
placed on Port 1. This is followed by a byte in the code memory will be en-
clock cycles. AS EL may then be driven series of programming pulses applied to
low which latches the high order bits of crypted with the first byte in the encryp-
the PGM/ pin (PO.l). These pulses are tion table, and so forth.
the address internally. The high address created by driving PO. 1 low and then
should remain on port 3 for at least two high. This pulse is repeated until a total Security Bits
clock cycles after ASEL is driven low. of twenty-five programming pulses have Two security bits, security bit 1 and se-
Port 3 may then be driven with the low occurred. At the conclusion of the last curity bit 2, are provided to limit access
byte of the address. The low address will pulse, the PGM/ signal should remain to the US ER EPROM and encryption
be internally stable 13 clock cycles later. high. key arrays. Security bit 1 is the program
The address will remain stable provided
inhibit bit, and once programmed per-
that the low byte placed on port 3 is The Vpp signal may now be driven to the forms the following functions:
held stable and ASEL is kept low. Note: VOH level, placing the 87C752 in the 1. Additional programming of the US-
ASEL needs to be pulsed high only to verify mode. (Port 1 is now used as an ER EPROM is inhibited.
change the high byte of the address. output port.). After 4 machine cycles (48 2. Additional programming of the en-
clock periods) the contents of the ad- cryption key is inhibited.
Port 1 is used as a bidirectional data bus dressed location in the EPROM array will
during programming and verify opera- 3. Verification of the encryption key is
appear on Port 1. inhibited.
tions. During the programming mode, it
accepts the byte to be programmed. 4. Verification of the USER EPROM and
The next programming cycle may now
During the verify mode, it provides the the security bit levels may still be
be initiated by placing the address infor-
contents of the EPROM location specI- performed.
mation at the inputs of the multiplexed
fied by the address which has been sup- buffers, driving the Vpp pin to the Vpp (If the encryption key array is being
plied to Port 3. voltage level, providing the byte to be used, this security bit should be pro-
programmed to Port 1 and issuing the 25 grammed by the user to prevent un-
The XTAl1 pin is the oscillator input and programming pulses on the PGM/ pin,
receives the master system clock. This authorized parties from reprogramming
bringing Vpp back down to the Vee level the encryption key to all logical zero
clock should be between 1.2 and 6 and verifying the byte.
MHz. bits. Such programming would provide
data during a verify cycle that is the
Programming Modes
The RESET pin is used to accept the logical compliment of the USER EPROM
The 87C752 has four programming fea-
serial data stream that places the contents.)
tures incorporated within its EPROM ar-
87C752 into various programming modes. ray. These include the USER EPROM for
This pattern consists of a 1O-bit code Security bit 2, the verify inhibit bit, pre-
storage of the application's code, a six- vents verification of both the USER
with the LSB sent first. Each bit is syn- teen byte encryption KEY array and two
chronized to the clock input, X1 . EPROM array and the encryption key
security bits. Programming and verifica- arrays. The security bit levels may still
tion of these four elements are selected be verified.
Programming Operation
Figures 5 and 6 show the timing dia- by a combination of the serial data
stream applied to the RESET pin and the
grams for the program/verify cycle.
RESET should initially be held high for at voltage levels applied to port pins PO. 1
least two machine cycles. PO.1 (PGM!) and PO.2. The various combinations are
shown in Table 3.
and PO.2 (Vpp) will be at VOH as a result
of the RESET operation. At this point,
February 1989 2-176

Programming and Verifying Port 1.7 contains the security bit 1 data fects, it is recommended that an
Security Bits and is a logical one if programmed and a opaque label be placed over the win-
Security bits are programmed employing logical zero if erased. Likewise, P1.6 dow. For elevated temperature or sol-
the same techniques used to program contains the security bit 2 data and is a vent environments, use Kapton tape
the USER EPROM and KEY arrays using logical one if programmed and a logical Fluorglas part number 2345-5 or equiv-
serial data streams and logic levels on zero if erased. alent. A/D performance is not guaran-
port pins indicated in Table 3. When pro- teed unless window is covered.
gramming either security bit, it is not E rasure Characteristics
necessary to provide address or data in- Erasure of the EPROM begins to occur The recommended erasure procedure is
formation to the 87C752 on ports 1 and when the chip is exposed to light with exposure to ultraviolet light (at 2537
3. wavelengths shorter than approximately angstroms) to an integrated dose of at
4,000 angstroms. Since sunlight and least 15W-sec/cm2. Exposing the
Verification occurs in a similar manner fluorescent lighting have wavelengths in EPROM to an ultraviolet lamp of
using the RES ET serial stream shown in this range, exposure to these light 12,000)1W/cm2 rating for 20 to 39 min-
Table 3. Port 3 is not required to be sources over an extended time (about 1 utes, at a distance of about 1 inch,
driven and the results of the verify op- week in sunlight, or 3 years in room level should be sufficient.
eration will appear on ports 1.6 and 1.7. fluorescent lighting) could cause inadver-
tent erasure. For this and secondary ef- Erasure leaves the array in an all 1s
state.
Table 3. Implementing Program/Verify Modes
Operation Serial Code PO.1 (PGMI) PO.2 (Vpp)

-,
Program user EPROM 296H Vpp
Program key EPROM 292H
-, Vpp
Verify key EPROM 292H VIH VIH
Program security bit 1 29AH
-, Vpp
Program security bit 2 298H -, Vpp
NOTE:
'Pulsed from VIH to VIL and returned to VIH.
EPROM PROGRAMMING AND VERIFICATION CHARACTERISTICS TA - 21°C to +27"C, VCC - 5V:±:10%, VSS - OV

1/tcLcL Oscillator/clock frequency 1.2 6 MHz
,
tAVGL Address setup to PO.1 (PROG-) low 10)15 + 24tCLCL
tGHAX Address hold after PO.1 (PROG-) high 48tCLCL
tOVGL Data setup to PO.1 (PROG-) low 38tCLCL
tGHOX Data hold after PO.1 (PROG-) high 36tCLCL
tSHGL Vpp setup to PO.1 (PROG-) low 10 )1s
tGHSL Vpp hold after PO.1 (PROG-) 10 )15
tGLGH PO.1 (PROG-) width 90 110 )15
tAVOV " Vpp low (Vcd to data valid 48tCLCL
tGHGL PO.1 (PROG-) high to PO.1 (PROG-) low 10 ~LS
tSYNL PO.O (sync pulse) low 4tCLCL

tSYNH PO.O (sync pulse) high 8tCLCL
tMASEL ASEL high time 13tCLCL
tMAHLO Address hold time 2tCLCL
tHASET Address setup to ASEL 13tCLCL
tAOSTA Low adress to address stable 13tCLCL
NOTES:
'Address should be valid at least 24tCLCL before the rising edge of PO.2 (Vpp).
"For a pure verify mode, i.e., no program mode in between, tAVOV is 14tCLCL maximum.
February 1989 2-177

87C752
VCC i - - + 5 V
1.0-1.10 PJ.Il-f>J.7
Vss
~
ADDRESS STROBE PO.O/ASEL
Pl.0-f>1.7 DATA BUS
PROCRAMMING
PULSES PO.l
Vpp /VIH VOLTAGE PO.2

SOURCE
Cll< SOURCE XTALI
Y RESET
CONTROL
LOGIC
1
I
RESET
XTALI
MIN 2 MACHINE
jo--CYCLES .1. TEN BIT SERIAL COOE -I
RESET~ N ~1~B~IT~0~~B~IT~1-L~B~IT~2-L~B~IT~J~I~B~IT~4~I~B~rr~5~I~B~IT~8~~B~IT_7~~B~IT~8~~BI~T~9~1______
PO.2 UNDEFINED I
PO. 1 UNDEFINED I
Figure 5. Entry Into ProgramNerify Modes
February 1989 2-178

"Tl
Cl> en
<D'
0- 0
2 ~ "g.
\I)
-<'" 0 en
<0
(j) s:
(;'
0> (3
<0 (j) '0
(3
::J ()
(Q \I)
(l)
I
~
'U
0
12.75V :::r 8.c:
()
PO.2 (Vpp) 5V
/ \ 5V
"0
CO
en
I
H tSHGL 25 PULSES H t GHSL CD
;::::;:
I
I I
~
'T1
iD:
PO,l (PGM) L ___ .5L.JL~TI..J o·
,
!;
co
!"
H t GLGH H t GHGL
0
(')
..
"'C
0
rtMASELl
98us MIN 1Qus MIN 0
::J
,.....
~~~7
~
.!. \!l., PO,O (ASEL)

\ 0
-..J
<0
3
~ tHASETI'
"l-
i tHAHLD ,
(l)
~
(")
X X
.
PORT 3 HIGH ADDRESS LOW ADDRESS
'<
n
HtADSTA H t DVGL
tGHDXI_
'I' tAVQV-j
PORT 1 INVALID DATA DATA TO BE PROGRAMMED INVALID DATA VALID DATA
I- +
VERIFY MODE PROGRAM MODE VERIFY MODE
'I' 'I
"0
~
3'
5'
0>
(j) ~
CO en
'0
-....,J \I)
o-...,J ()
:::;;
(;'
<.T1
I\.)
o·~
"
Signetics Section 3
Application Notes
INDEX
AN408 SC80C451 Operation of Port 6 ..................... 3-1
AN417 256K Centronics Printer Buffer-
Using the SC87C451 Microcontroller . . . . . . . . . . . . . . .. 3-12
AN418 CounterfTimer 2 of the 83C552 . . . . . . . . . . . . . . . . . . .. 3-26
AN420 Using up to 5 External Interrupts on 8051 Family
Microcontrollers .............................. " 3-33
Signetics AN408
SC80C451 Operation of
Port 6
Application Note
INTRODUCTION OPERATION Figure 1 shows one possible example of an

The features of the 80C451 are shared On reset. port 6 is programmed correctly for 80C451 on a memory bus. This arrangement
with the 80C51 or are conventional ex- use as a bus interfaca (see Figure 2). This allows the main processor to query port 6 for
cept for the operation of port 6. The prevents the interfaca from disrupting data on flag status without interrupting the 80C451. If
flexibility of this port facilitates high- the bus of the host processor during power- the address decoder. shown in Figure 1.
speed parallel data communications. This up. Software initialization of the CSR (Control enables port 6 on the 80C451 when the
application note discusses the use of Status Register) is not required. A dummy address is 6000H or B001 H. and the address
port 6 and is divided into the following read of port 6 may be required to clear the line AO controls the port select feature. then
sections: the host processor can read and write to port
IBF (Input Buffer Full) flag since it could be
1. Port 6 as a processor bus interface. set by tum on transients on the bus of the 6 using address BOOOH. Since the port select
2. Using port 6 as a standard pseudo bi- function Is being controlled by the address
host processor. On reset the CSR of the
directional I/O port. Mne AO. the CSR contents can be read by the
63C451 is programmed to allow the following:
3. Implementation of parallel printer host processor at address 6001 H.
ports. 1. AFLAG is an input controlling the port
This information applies to all versions of select function. If AFLAG is high. the By testing the CSR contents in this way. the
the part: 80C451, 83C451 and the 87C- contents of the CSR is output on port 6 host processor can tell if new data has been
451. when the port is read by the host. If wriIIento the port 6 output latch Since it last
PORT 6 AS A PROCESSOR AFLAG is low. then the contents of the read the port or if the 80C451 has read the
BUS INTERFACE output latCh is output when port 6 is read last byte that the host wrote to the port.
Port 6 allows use of the 80C451 as an by the host. Conversely the BOC451 can poll the flags in
element on a microprocessor type bus. 2. BFLAG is an input controlling· the port its CSR to see if the host processor has
The host processor could be a general enable function. In this mode when written to or read from port 6 since the last
purpose MPU or the data bus of a
BFLAG is high. the input latCh and the lime It serviced the port.
microcontroller like the 80C451 itself.
output drivers are disabled and the flags
This feature allows single or multiple If desired. an interrupt sourca for the B0C451
are not affected by the ~ (Input Data
80C451 controllers to be used on a bus can be derived easily from the port enable
as flexible peripheral processing ele- Strobe) or ~ (Output Data Strobe)
sourca as shown by the dashed line in Figure
ments. Applications could include key- signals. When BFLAG is low. the port is
1.
board scanners, serial I/O controllers, enabled for reading and writing under the
servo controllers, etc. control of ~ and DDS pins.
HOST
PROCESSOR
• ..
Ill!
WI!
r--
r--- I
-~
WI! Ill!
,
DO-D7
,, I
sa IIlIIIlIIIPI
(AFLAII)
~
i"-
f--
-- -
74HCT373
LA1tlH ill!
r-- 811. e0C451
ADDRESS
~
II!
ADDRESS (BF1.AO) IIIT6
,A- ~
ADO-AlJ7
ALE
,
D!
NJ
iliL -'" - t __ Jt
AI-/IA
o...._
II j,.
" "'"---
Figure 1. An 83C451 on 8 Microprocessor Memory Bus
February 1989 3-1

Signetics Microprocessor Products Application Note
Operation of Port 6 SC80C451
SOFTWARE EXAMPLES Input buffer luliliag (CSR bit 0). lIthe flag is Conversely tha 80C451 polls the ISF flag and
To write to port 6 on the bus shown in Figure clear the host writes a byte to address reads a byte from port 6 when ~ finds the flag
I, the host processor first reads the CSR 8000H. This loads the input buffer latch of set. The flag is automatically reset when this
contents at address 8001 H, and tests the port 6 and sets the input buffer full flag. internal read 0CCUfS.
80C451 ROUTINE TO READ ONE BYTE FROM HOST VIA PORT 6

RCVR: JNS CSR.O,RCVR ;TEST ISF FLAG
MOV A,P6 ;WHEN FLAG IS SET READ BYTE
RET
8OC51 ROUTINE TO WRITE ONE BYTE TO THE 83C451 PORT 6

If the host processor is an 8OC51 the loIlowing routine will write a byte of date to the 80C451. The date involved is passed to the routine through
register 1.
XMIT: MOV OPTR,8001 H

TEST: MOVX A,@OPTR ;REAO THE CSR
JS ACC.O,TEST ;TEST ISF FLAG
MOV OPTR,8000H
MOV A,Rl
MOVX @DPTR,A ;WRITE DATA TO THE 451
RET
80C451 ROUTINE TO WRITE ONE BYTE TO HOST VIA PORT 6

Routines for date transfer in tha opposite direction are similar to the above two. The 80C451 version is given below.
XMIT: JS CSR.l,XMIT ;TEST OBF FLAG

MOV P6,A ;WRITE DATA
RET
CSR 7 CSR 6 CSR5 CSR 4 CSR 3 CSR 2 CSR 1 CSRO

MBI MBO MAl MAO OBFC IOSM OBF IBF
1 1 1 1 1 1
FIgure 2. CSR Programmed to Allow Port 6 a. a Bua Interface
February 1989 3-2

USING PORT 6 AS A
STANDARD QUASI·
BIDIRECTIONAL 1/0 PORT
To use port 6 as a common II 0 port, all 01 the
control pins are tied to ground (see Figure 3).
On hardware reset, bits 2 - 7 in the CSR are
set to one. Port operation and electrical
characteristics become identical to port 1 on
the aOCSl and the 80C451 ports I, 4, and 5.
No software initialization is required.
" desired, AFLAG and BFLAG can be used Figure 3_ Standard I/O Port on Reset Figure 4. Standard 110 Port on Reset
as outputs while port 6 is operating as a with AFLAG and BFLAG as Outputs
standard quasi-bidirectional 110 port (see Fig-
ure 4). In this case, only iDS and ODS are tied common printer to be handled by a single
chip: 4. The RAM addressing ability 01 ports 0
to ground and the CSR is initialized to allow and 2 can be used to address up to 64K
operation 01 AFLAG and BFLAG as simple 1. The features 01 port 6 allow a parallel
bytes 01 a hardware buffer/spooler. AF-
outputs (see Figure 5). printer port to be designed with only line
LAG and BFLAG as simple outputs (see
driving and receiving chips required as
Figure 5).
additional hardware.
5. The 64K byte ROM addressing capability
IMPLEMENTATION OF 2. The onboard UART allows RS232 inter-
allows space for the most sophisticated
PARALLEL PRINTER PORTS facing with only level shifting chips add-
software.
USING PORT 6 ed.
The 80C451 is an excellent choice lor a 3. The B-bit parallel ports 0 to 6 are ample In addition, either end 01 a parallel interface
printer controller. The 80C451 has the lacili- to drive onboard control functions, even can be implemented using port 6, and the
ties to permit all 01 the intelligent leatures 01 a when ports are used for external memory interfaces can be interrupt driven or polled in
access, interrupts and other functions. either case.
eSR 7 eSR 6 CSR 5 CSR 4 CSR 3 CSR 2 CSR 1 CSR 0

0 X 0 X X 1
Figure 5_ CSR Programmed to Allow AFLAG and BFLAG to Operate as Outputs and Port 6 as a Standard 110 Port
DATA TRANSFER SIGNAL PINS TYPICAL AUXILIARY PIN FUNCTIONS

Ground Return
Pin No. Pin No. Signal Pin No_ Signal
1 19 ~ 12 PAPER OUT
2 20 DATA 1 14 AuTO LlN~ "EED
3 21 DATA 2 16 LOGIC GROUND
4 22 DATA 3 17 CHASSIS GND
5 23 DATA 4 30 GROUND RETURN
6 24 DATA 5 31 ~~SEi l5~iNTER
7 25 DATA 6 32 ~
a 26 DATA 7 33 GROUND RETURN
9 27 DATA a 36 ~
10 2B ACKNLG
11 29 BUSY
Figure 6. Parallel Prtnter Interface Pin Functions
February 1989 3-3

TAANSMmER GENERATED SIGNALS
DATA_
STROBE _ _ P~~t~~=V-,,::O;::;;'I~-l-+------------
>r_
RECEIVER GeNERATED SIGNALS
HANDSHAKE TYPE 1
: -----J/----------t-,..--~-f-=-y-
HANDSHAKE TYPE 2
BUSY ,r --- - - - - -~- - - "'C ~~

----1===v- WF'"""
Figure 7. Parallel Printer Interface Signals
THE INTERFACE printers using generic parallel interfaces. This Type 2 - Another style of handshake gener-
Data transfer on a parallel printer interface fact influences the design of both port hard- ates a busy signal only when the printer will
occurs across eleven signal lines. The other ware and software. A good transmitter should not be aple to accept more data for a
conductors on the standard plug are used as be able to drive devices with all three styles relatively long time. Acknowledge pulses are
ground returns or for auxiliary functions (see of handshakes and a good receiver should created after every byte received. When the
Figure 6). Only the data transfer signals will generate the handshake most likely compati- busy signal is generated after a byte is
be considered. ble with any transmitter. received, the associated acknowledge pulse
does. not occur until after the busy signal
The Data Transfer Format The Variations returns to logic zero. (see Figure 7).
The parallel printer interfaces are far more Type 1 - Figure 7 shows a common style of
standardized in features than their serial handshake and is the style that will be imple- Type 3 - A third handshake style does not
counterpart. However at least three signifi- mented in the receiver examples. A busy generate acknowledge pulses. but a busy
eant variations exist in handshake style in signal and an acknowledge strobe pulse are signal is produced after every byte is re-
generated for every byte received. ceived.
February 1989 3-4

PARALLEL PRINTER The GSR is programmed to the output only 3. The OBF is cleared on the positive edge
mode. In this mode the ODS pin does not of the ODS input.
INTERFACES USING POLLING
control the output drivers but only the output 4. The IBF flag is cleared on the negative
Transmitter Operation buffer full flag. The flag serves to record the edge of the lOS strobe.
This application illustrates the flexibility of the positive transition of the acknowledge signal.
port 6 logic in solving an applications prob- The input latch is not used, but the IDS pin is NOTE:
lem. We need to be able to handle all types of used to set the input buffer full flag. This is With this combination of modes set, port 6 is
acknowledge signals that might be received used to record the negative transition at the in the output only mode.
by the transmitter. We will use the ODS pin end of the busy signal. Dummy reads by the Receiver Operation
and output buffer full flag logic to record the 80C451 of port 6 will be used to clear the flag. In receiver operation, the IDS input is used to
receipt of the acknowledge pulse (see Figure In this example, the AFLAG mode is set only latch in the data transmitted on receipt of the
8), but not all parallel receivers generate to place the port in the output only mode. The strobe pulse. The receiver's GSR is pro-
acknowledge pulses. We could poll the busy AFLAG pin is not actually used (see Figure grammed to allow the following:
signal line, but not all receivers generate busy 10). 1. The input buffer full flag is output through
signals for each byte received; so lack of a
The transmitter's GSR (control status regis- the BFLAG pin and is used as the busy
busy signal does not imply that we can send
ter) is programmed to the following mode signal to the transmitter.
another byte. We can, however, expect an
(see Figure 9): 2. The IBF flag is set and data is latched on
acknowledge pulse very shortly after the end
of a busy signal if one is going to arrive at all. 1. GSR bit 6 controls the BFLAG output and the positive edge of IDS.
So we can send a new data byte after having therefore the strobe line. 3. Writing to the GSR bit 4 controls the
received either a positive transition on the 2. The OBF (output buffer full) flag controls AFLAG output and therefore the ac-
acknowledge line, or shortly after receiving a the AFLAG output. knowledge line.
negative edge on the busy line.
BUS BUS
DRIVER RECEIVER
AFLAG
TRANSMITTER RECEIVER
Figure 8. Interconnection for a Parallel Interface Using Polling
CSR 7 CSR 6 CSR 5 CSR 4 CSR 3 CSR 2 CSR 1 CSR 0

0 1 1 0 0 1
Figure 9. CSR Programmed for Polled Transmitter Operation
February 1989 3-5

Figure 10. Flow Chart of Polled Parallel Transmitter Operation

MBI MBO MAl MAO OBFe IOSM OBF IBF
1 0 0 1 1 0
Figure 11. CSR Programmed for Polled Parallel Receiver Operation
February 1989 3-6

Figure 12. Flow Chart of Polled Parallel Receiver Operation
SOFTWARE EXAMPLES
This polled parallel transmit routine outputs one byte passed to it in the accumulator.
MOV CSR,#OS4H ;INITIALIZE PORT S OPERATING MODE
JB P5.0 ;WAIT IF BUSY SIGNAL IS HIGH
MOV PS,ACC ;OUTPUT DATA
MOV R1,PS ;DUMMY READ TO CLEAR IBF FLAG
MOV R1,#02H ;INITIALIZE DELAY COUNTER
CLEAR CSR.S ;START STROBE PULSE
DJNZ R1,$ ;TIME S MICROSECOND STROBE PULSE
SETB CSR.S ;END STROBE PULSE
WAIT: JNB CSR.1.0UT ;EXIT IF ACKNOWLEDGE RCV'D
JNB CSR.O.WAIT ;EXIT IF NEGATIVE BUSY EDGE RCV'D
RET
This polled parallel receive routine places one byte in the accumulator each time it is called.
P INIT: MOV CSR,#09CH ;INITIALIZE PORT S OPERATING MODE
MOV R7,PS ;DUMMY READ TO CLEAR IBF FLAG
PIN: JNB CSR.O ;INPUT BUFFER LATCH FULL?
CLR CSR.4 ;BEGIN ACKNOWLEDGE PULSE
DJNZ R7,$ ;TIME ACKNOWLEDGE PULSE
MOV A,PS ;READ BYTE - CLEAR BUSY SIGNAL
DJNZ R7,$ ;TIME ACKNOWLEDGE PULSE
SETB CSR.4 ;END ACKNOWLEDGE PULSE
RET
February 1989 3-7

INTERRUPT DRIVEN PARALLEL transmitter that another byte may be transmit- 1. The input buffer full flag is output through
ted. The transmitting 83C451 is free to do the BFLAG pin and is used as the busy
PRINTER INTERFACE
other tasks prior to this interrupt. signal to the transmitter. The IBF flag is
Transmitter Operation set and data is latched on the positive
In this routine, Figure 15, the main program
The transmitter's CSR (control status regis- edge of IDS.
establishes a buffer in data memory ended by
ter) is programmed to the following mode 2. Writing to the eSR bit 4 controls the
an ASCII end of text character. To begin
(see Figure t4): AFLAG output and therefore the ac·
outputting the buffer the routine PSEND is
1. CSR bit 6 controls the BFLAG output and called. The rest of the buffer is emptied by the knowledge line.
therefore the strobe line. interrupt vectors to PSENDI. The receiver is interrupted on the negative
2. The OBF (output buffer full) flag controls edge of the data strobe. Data is latched in on
the AFLAG output. For printers which generate acknowledge
pulses, output rates of 25k transfers per the positive edge of the strobe pulse (see
3. The OBF is cleared on the positive edge Figure 17). Since the strobe pulse is normally
second are achieved. Timer generated inter·
of the ODS (output data strobe) input. very short there is little time lost between
rupts are used to periodically return program
4. Tha IBF flag is set on the negative edge execution to the routine to service non-ac- receiving the interrupt and having valid data in
of the IDS (input data strobe) pin. knowledging printers and to provide a timeout the input latch. The receiver is free to do
feature. Non acknowledging printers are ser- other tasks prior to receiving the INTO inter·
NOTE:
viced at a rate of about 2.5k transfers per rupt.
With this combination of AFLAG and BFLAG
modes set, port 6 is in the output only mode. second. This maximum rate may be varied by
The output drivers are always enabled and adjusting the timer reload value. As written,
the time out procedure attempts to retransmit SOFTWARE EXAMPLES
the 008 input is only used to clear the OBF
a byte when the printer has not acknowl- The software for the interrupt driven parallel
flag.
edged for an excessively long time. receiver is similar to the polled receiver exam-
INTO is programmed to be negative edge ple. However, after an interrupt is received,
sensitive and is connected to the OBF flag Receiver Operation this routine checks to confirm that data has
through the AFLAG pin. The OBF is cleared In receiver operation, the iDS input is used to been latched by the positive edge of the
on the positive edge of 008. The net result is latch in the data transmitted on receipt of the strobe pulse before proceeding with the rou-
that INTO is triggered on the end of the ACK strobe pulse. The receiver's CSR is pro- tine.
pulse (a positive edge). This signals the grammed to allow the following (see Figure
16):
lm 1.-<l-f-"':'::;;':"+-<3---I AFLAG
BFLAG >--+-=-=-+-.... :>-.... ~

iIiTli
Ifm
~ t-t-<t-i-=:;';"'-i--<a--; BFLAG
P6 P6
BOC451 BOC451
BUS BUS
DRIVER RECEIVER
TRANSMmER RECEIVER
Figure 13. Interrupt Driven Parallel Interfaces Using 80e451 Controllers
February 1989 3-8


!'~'
MB1 MBO MA1 MAO OBFC IDSM OBF IBF
0 1 1 0 1 1
Figure 14. CSR Programming for Use as an Interrupt Driven Parallel Transmitter
SET DPTR TO
START OF RAM
BUFFER
DISABLE
INTERRUPTS
STOP AND
RESET TIMER
IIE·PULSE INCREMENT WRITE BYTE

STROBE TID COUNTER TOPS
ENABLE INTO,
START STROBE
DISABLE INTO
INCREMENT DPTR
END STROBE
START TIMER.
ENABLE
INTERRUPTS
RETURN TO
INTERRUPTED
PROGRAM
Figure 15. Flow Chart for an Interrupt Driven Parallel Transmitter
February 1989 3-9

C5R 7 C5R 6 C5R 5 C5R 4 C5R 3 C5R 2 C5R 1 C5R 0

MB1 MBO MA1 MAO OBFC 105M OBF IBF
1 0 0 1 1 0
Figure 16. C5R Programming for Use as an Interrupt Driven Parallel Receiver
Figure 17. Flow Chart of Interrupt Driven Parallel Receiver Operation
SOFTWARE EXAMPLES
The software for the interrupt driven parallel receiver is similar to the polled receiver example. However, after an interrupt is received, this routine
checks to confirm that data has been latched by the positive edge of the strobe pulse before proceeding with the routine.
INIT: MOV CSR.#090H ;INITIALIZE CSR

SETS EXO ;ENABLE INTERRUPT 0
SETB ITO ;SET NEG EDGE TRIGGERED INTERRUPTS
SETS EA ;ENABLE ALL INTERRUPTS
ORG EXTIO ;INTERRUPT 0 VECTOR
JMP RCVR
RCVR: JNS CSR.O,$ ;CONFIRM DATA LATCHED
CLR CSR.4 ;START ACKNOWLEDGE PULSE
MOV R7,#02H ;INITIALIZE THE DELAY COUNTER
DJNZ R7,$ ;TIME ACK PULSE
MOV A,P6 ;READ BYTE - RESET SUSY LINE
MOV R7,#02H ;INITIALIZE THE DELAY COUNTER
DJNZ R7,$ ;TIME ACK PULSE
SETB CSR.4 ;END ACK PULSE
RETI
February 1989 3-10

This is the software for the interrupt driven parallel transmitter example.
; XMIT ROUTINE DRIVEN BY ACK PULSE GENERATED INTERRUPTS, OR TIMER GENERATED INTERRUPTS
; FOR NON ACKNOWLEDGING PRINTERS. READS DATA BUFFER IN EXTERNAL RAM STARTING AT 100H
; AND READING UNTIL 04H IS FOUND.
ORG RESET
JMP 26H
ORG TIMERO
JMP PSEND1
ORG EXTIO
JMP PSEND1
ORG 26H
MOV CSR,#064H ;PORT 6 MODE
MOV TMOD,#002H ;CONFIGURE TIMER 0 TO 16 BITS
SETB TOO ;INTO IS EDGE TRIGGERED
SETB EA ;ENABLE INTERRUPTS
PSEND: MOV DPTR,#0100H ;SET DPTR TO START OF TEXT
;BUFFER
PSEND1: CLR EA ;DISABLE INTERRUPTS AND STOP
;TIMER
CLR TRO ;IF ENABLED
CLR ETO
MOV R7,00H ;CLEAR TIMEOUT COUNTER
MOV R6,00H
MOV THO,#-4 ;SET TIMER INTERRUPT PERIOD
MOV TLO,#OOH
JB OCBH,BB ;BUS BUSY
MOV ACC,#OOH ;CLEAR ACCUMULATOR
MOVX A,@DPTR ;RETRIEVE FIRST BYTE
MOV P6,ACC ;OUTPUT FIRST BYTE
CJNE A.#004H, CONT1 ;LOOK FOR END OF TEXT
JMP EOTB
CONT1: SETB EXO ;ENABLE INTO
CLR OEEH ;START STROBE PULSE
INC DPTR
MOV ACC,DPH ;LOOK FOR PHYSICAL END OF
JB ACC.2,EOTB ;TEXT BUFFER
SETB OEEH ;END STROBE PULSE
JMP CONT
EOTB: CLR EXO ;END OF TEXT FOUND, DISABLE
;INTO
SETB OEEH
SETB EA
RETI
BB: INC R7 ;COUNT TIMER TIMEOUTS ON
;BUS BUSY
CJNE R7,#00H, CONT ;LOOK FOR OVERFLOW
INC R6 ;COUNT OVERFLOWS
CJNE R6,#10H, CONT ;TIMEOUT APPROX 5 SEC
JMP TO
CONT: SETB TRO ;ENABLE TIMER INTERRUPT
SETB ETO ;START TIMER
SETB EA
RETI
TO: CLR OC9H ;SEND NEW STROBE PULSE IN
;RESPONSE TO TIMEOUT
NOP
NOP
MOV R6,#OOH ;RESET TO COUNTER
MOV R7.#OOH
SETB OC9H ;END OF STROBE PULSE
JMP PSEND1
February 1989 3-11

Signetics AN417
256K Centronics
Printer Buffer
Using the SC87C451
Microcontroller
Microprocessor Division Application Note
DESCRIPTION In this note, port 6 is used in the 1/0 using a dummy MOVX @RO,A (move to
This application note describes a stand mode as a Centronics compatible printer external data memory) instruction. This
alone Centronics type parallel printer output port. Additionally, the liDS and allows DRAM refresh to be done much
buffer using the Signetics SC87C451 ex- BFLAG pins normally associated with more quickly than would otherwise be
panded 1/0 microcontroller. This type of port 6 are used as part of the input port possible.
unit would typically be placed between a logic. For a complete discussion of port
personal computer and its printer. It cap- 6 operating modes and programming, Port 1 and one bit from port 4 form the
tures the data to be printed at high see the Signetics application note AN- 9-bit address required when addressing
speed, freeing the personal computer to 408 titled "SC83C451 Microcontroller- the DRAM array. The data inputs to the
go on to other tasks, and sends data to Operation of Port 6". array come from the parallel input data
the printer as required. As described lines which are latched by U4. The RAM
here, 256K dynamic RAMs are used, Circuit Description data outputs are fed to port 5. By mak-
providing over one quarter million char- Figure 1 is a schematic diagram of the ing the data outputs available to the
acters of storage. If desired the design is printer buffer circuit. Other than the processor, it is possible to add some ad-
easily modified to work with 1 megabit 87C451 (U1), and the eight 256K DRAMs ditional features to the firmware, such as
DRAMs. Although written with the 87C- (U5-U12). only two 74LS244 buffers control codes for printing multiple copies
451 in mind, this design is applicable to (U2, U3) and a 74HCT374 (U4) octal flip of a document, data compression, data
the 80C451 and 83C451. flop are needed. The U2 and U3 buffers conversion, etc. which are not imple-
are included to provide full drive capabil- mented in this design.
Design Objectives ity for the output port and some of the
The objectives kept in mind during the handshake signals on the input port, as Port 6 Operation
design of this device were: provide a the output buffers on the 87C451 can The liDS (input Data Strobe) and
substantial size of buffer, keep the parts only drive 3 LSTIL loads. U4 has 8-bit BFLAG pins are normally used in con-
count and the power consumption to a data strobed into it by the ISTB pulse of junction with the port 6 bidirectional
minimum, and use readily available com- the input port. mode. In this mode, the liDS pin is used
ponents. to strobe data into the port 6 input
As the code size for this application is latches, and BFLAG is used as flag out-
A buffer size of 256k bytes was chosen quite small (less than 1 K bytes). the on put. In this application however, these
because, although a 64K byte buffer is chip instruction memory is quite suffi- two bits are used to good effect as part
very easily implemented using the 8051 cient for program storage. For a produc- of the (separate) input port logic. When
family's 64K external data storage capa- tion version, the 87C451 could be re- a byte of data is strobed into U4 by the
bilities, it is a little too small for today's placed with the Signetics 83C451 with a printer port of the host computer, the
printing applications that print a page of 4K X 8 masked ROM on chip. Note that ISTB signal connected to liDS sets the
text in graphics mode, using up twenty Port 0 and Port 1 are not used in the input buffer full flag (IBF). BFLAG is
times as many bytes as standard printing present design, thus the 80C451 may be programmed to mirror the contents of
mode. Presenting a method for control- used in this application with the addition I BF, and therefore becomes asserted.
ling 256K DRAMs shows off the 1/0 ca- of an external address latch and E- This makes it ideal to be used as the
pabilities of the 87C451, and it is very PROM. BUSY output for the input port. After the
easy to add the extra address line for input port data has been read and stored
one megabit devices if a larger buffer is The IRAS, ICAS, and IWR signals for in the RAM buffer, BFLAG is de-asserted
needed. the DRAM array are provided by port 3 by performing a dummy read of port 6,
bits IWR, IRD, and n. Note that as in which clears IBF. To complete the input
The SC8XC451 Microcontroller the 80C51 , all port 3 signals are mlti- port logic, one of the port 3 pins, P3.4 is
The 8XC451 is an 8-bit microcontroller functional. That is, each can be treated used as the acknowledge signal, and is
based on the familiar 8051 family of de- a regular quasi-bidirectional port bit, or assertedl de-asserted by software. The
vices. In fact, it is an 80C51 with three as having the special function indicated 10DS pin is tied to ground to permanent-
added ports: P4, P5 and P6. Ports 4 and by its name. This feature is an advan- ly enable the port 6 output drivers. This
5 give 12 (16 in PLCC) additional quasi- tage when using IWR and IRD as IRAS does not cause difficulty as no data is
bidirectional 1/0 lines. Port 6 provides and ICAS control signals for a DRAM being inp"t into the port.
another 8 bits of 1/0, plus 4 handshake array. Treated as a normal port bit, the
lines that can be programmed to operate IWR pin is cleared and set by individual Note that programming port 6 to operate
in several useful modes for interfacing. CLR and SETB instructions for a normal in the bidirectional mode as described
The 8XC451 comes in three versions; length RAM read or write cycle. How- above means the loss of laDS as an
ROM-less 80C451, 83C451 with 4K x 8 ever, when performing a refresh cycle, acknowledge input. The acknowledge
ROM, and 87C451 with 4K x 8 EPROM. IRAS (port 3 /WR) can be pulsed low input is normally used to clear the OBF
February 1989 3-12

256K Centronics Printer Buffer SC87C451

(Output Buffer Full) flag, indicating that ister to be at the lower interrupt level so necting a daisy-wheel printer to the se-
the printer is ready for another charac- it cannot prevent refresh service. The rial port, a dot-matrix printer to the par-
ter. On the other hand, operating port 6 interrupt a service routine stores the in- allel port, and sending an "address" flag I
in the "output only" mode causes the put character at the next location in the in the file header, simultaneous letter- I"
loss of BFLAG as BUSY output. Because DRAM array, using the technique of a quality and draft printing could be done.
the input port requires an instant BUSY circular FI FO buffer. The routine also
indication while the output port only sends back an acknowledge pulse by The size of the DRAM array is easily
needs to remember the occurrence of clearing and setting the P3.4 pin, and expanded to one megabyte or larger de-
an acknowledge pulse, it makes sense then clears the BUSY (BFLAG) pin by vices by connecting the additional ad-
to program port 6 to operate in the performing a dummy read of port 6 (un- dress pins to port 4 bits 1 and 2. Only
bidirectional mode, with 10DS grounded less this character caused the buffer to slight modifications to the operating firm-
to enable the output drivers. The II NTI be completely full). ware would be required.
pin can be used instead of 10DS to
record the occurrence of an acknowl- During periods of access to the DRAM Conclusion
edge pulse with the interrupt system. array by the input and output routines, The Signetics SC8XC451 microcontrol-
the global interrupt enable bit (EA) is lers provide plenty of 110 pins that pre-
Priority and Execution of Tasks cleared so that the refresh interrupt does viously had to be implemented by clumsy
There are three tasks that must be per- not disturb the contents of ports 1 and 4, 1/0 expansion methods. The flexibility of
formed in this system: Receive - servic- or the IRAS, ICAS, and IWR signals. port 6 means that this device can be
ing the input port and storing the input used in a wide variety of applications
character, Transmit - sending stored The printer (output port) service routine requiring special port functions, while still
characters to the output port as re- runs all the time, except when the CPU using the industry standard 8051 instruc-
quired, and Refresh - performing DRAM is called to service the other conditions, tion set.
refresh. The timers and interrupt system therefore having the lowest priority. If
are used to manage the execution and there are characters in the buffer, polling This App Note, describing a typical par-
priority of these tasks. Figure 2 illus- is used to check for output port BUSY allel printer buffer makes full use of the
trates the flow charts for each task. Fig- status. If the printer is not busy, then the 8XC451 features, yet allows room for en-
ure 3 is a listing of the firmware code, character is sent, and the output port hancement and expansion.
which breaks up into sections performing ISTB pin (P4.3) is cleared and set. The
these three functions, as well as an ini- output port lACK line is connected to
tialization section. the IINTI pin, so that the negative going
edge of the lACK signal is recorded as
The 51C256 DRAMs require a 256 row an interrupt pending. A very short I NT!
refresh every 4 milliseconds. Rather than service routine sets a software flag to
do an entire refresh cycle every 4 milli- indicate that the printer acknowledge
seconds, it is done as 64 rows every the last character.
millisecond. This leaves time for other
tasks to get service "slices" more fre- Possible Enhancements
quently. As DRAM refresh is obviously There are a number of features that
the highest priority, timer 0 is used as could be added to this design. As men-
the refresh interval timer, and is pro- tioned previously, the microcontroller
grammed to the 16-bit mode, and set to could be put into the idle mode when the
the higher priority level in the Interrupt buffer is empty. conserving power.
Priority (IP) register. The refresh code is
written in-line rather than in a loop to The software could be enhanced to pro-
maximize speed. vide features such as multiple copies off
a document, data compression, data
An interesting point to note is that when conversion, automatic printer setup, etc.
there are no characters stored, the The PC operating system could be suita-
DRAM does not need to be refreshed. If bly modified to send a header for each
power consumption is of concern, the file to be printed, containing these pa-
87C451 could be programmed to go into rameters. There is plenty of room for op-
idle mode whenever the buffer were erating firmware expansion, and plenty
empty. A character strobed into the in- of horsepower left in the 87C451 to han-
put port would cause an interrupt, re- dle these features.
starting the 87C451; DRAM refresh
would be maintained until the buffer was The two serial port pins RxD and TxD
once again empty. were deliberately left unused so that in-
put andlor output ports are easily imple-
The next highest priority should be input mented for serial interfaces or printers
port service, as the reason for having a using the built-in UART. The pins used
printer buffer is to get the data out of for parallel port handshaking could then
the computer as quickly as possible. be used as serial handshaking lines, pro-
Therefore, the input port ISTB signal is viding the standard "modem" signals.
connected to the IINTO pin (as well as
U4's clock pin and liDS). Interrupt a is Combining the above two features, this
programmed in the I nterrupt Priority reg- circuit could act as a "splitter". By con-
February 1989 3-13

Tl
Cl> (J)
cr I\)
.... iD'
(]l :::l
c (j) ~
~ ri'
'< A (J)
.... DB25 () i!::
'"
co 1S p------.----------, CD
ri'
a
'" 2J 18U~? ~ SLCT
::m fERROR
~Cl
P4,J
0
: ::J
.-+
fINT1~ 18
UJ ~' i oPE
BUSY
0
:
..... ~
0
87C451~.1 ~~CK
PLCC PS.5
PM
~g]
C> U2 0
og~
08
05 PRINTER
OUTPUT
PORT
:
:
::J
0
(J)
~
'0
a
c
P6.1 741.S244 02 "U 0
PS.o 55 OEa OEb 0 01 :::::!, en
IODS~ 4...he %s ::J
AFLAG 58 8 J
,I),
-
- -
-
I 1 0
1.-----------------'
0 0
.-+
CD
.....
1. 12L14
~ rn
c
-+>
." -+>
eli' CD
e:: .....
;
~
(f)
n !L !L 14
v.> ::r !L !L !L 14Q 8X
Q
....
I ~
3
Q Q Q Q Q
-:}:
51C258 OR 4125S
.I> 2l.
n' Voo
0
iii'
'!lIl>
US U7 U8 us U10 U11
U12 kT..L EACH
0.11£
Vss 18 DRAM
3
INPUT
PORT
(J)
~ ()
ex> ~ri'
-....j
~
() 0'
:::l
~
(]l Z
...... ;
o
Figure 2. Flowchart of Transmit Operation
February 1989 3-15

REPEATED
64 TIMES
Figure 2. (Cont) Flowchart of Receive and Refresh Operation
February 1989 3-16

j*******************************************************i
256K PRINTER BUFFER PROGRAM USING THE 8xC451 I~

FOR CENTRONICS PARALLEL PRINTER PORTS
SIGNETICS CORPORATION
October, 1988
i*******************************************************i
$Mod451
$Title(8XC451 Printer Buffer)
$Date(lO/28/88)
PORT USAGE:
PO Not used (reserved for data/address bus when external

program memory is used).
PI Lower S bits of DRAM address (AO - A7).
P2 Not used (reserved for high-order address bus when external
program memory is used).
P3.0 (Reserved for serial port.)

P3.1 (Reserved for serial port.)
P3.2 (/INTO) Input port strobe input (interrupt).
P3.3 (/INT1) Output port acknowledge input (interrupt).
P3.4 Input port acknowledge output.
P3.5 DRAM write enable output.
P3.6 (/WR) DRAM row address select output.
P3.7 (/RD) DRAM column address select output.
P4.0 Upper bit of DRAM address (AS).

P4.1 Reserved as an extra address line for I Megabit DRAMS.
P4.2 Not used.
P4.3 Output port busy input (OBUSY).
P4.4-P4.7 Unused (not available on 64-pin DIP package).
p5 DRAM output data.
P6 Parallel output port.

/IDS Input port strobe input (ISTB).
BFLAG Input port busy output (IBUSY).
AFLAG Output port strobe output (OSTB).

/ODS Port 6 output enable, tied low.
Internal Register/RAM Usage:
REFCNT EQU 020h Low order refresh byte.
The following refer to the circular FIFO buffer

implemented in the DRAM array.
INLOW EQU 22h Incoming address low byte.

INMID EQU 23h Incoming address mid byte.
INHI EQU 24h Incoming address high byte.
OUT LOW EQU 25h Outgoing address low byte.
OUTMID EQU 26h Outgoing address mid byte.
OUTHI EQU 27h Outgoing address high byte.
February 1989 3-17

OACK EQU 28h Holds flag for output port acknowledge.

FOACK BIT OACK.O Bit-address of output port acknowledge flag.
; Miscellaneous Equates:
TIME EQU -1000 Value for 1000 timer clocks 1 millisecond.

TIMEHI EQU HIGH TIME High byte of timer value.
TIMELO EQU LOW TIME Low byte of timer value.
RAS BIT P3.6 DRAM column address select.
CAS BIT P3.7 DRAM row address select.
DRAMWR BIT P3.5 DRAM write control line.
IACK BIT P3.4 Input port ACK output.
ISTB BIT P3.2 Input port strobe line (INTO).
OBUSY BIT P4.3 Output port BUSY input.
OSTB BIT MAO Output port strobe (MAO bit in port 6 CSR).
i***************************************************** ***********************
Reset and Interrupt Jump Table
ORG OOh ; Power-on reset.

AJMP START
ORG 03h INT O.

AJMP INDATA Data at input port.
ORG OBh Timer O.

AJMP REFRESH Refresh DRAM array.
ORG 13h INT 1.

AJMP OPACK Output port acknowledge.
i***************************************************** ***********************
Power up reset routine:

Set up refresh timer, enable timer interrupt and
external interrupt, initialize circular buffer pointers.
ORG 18h
START: MOV SP,#40h Initialize stack pointer.
MOV A,#OO
MOV REFCNT,A Initialize refresh counter.
MOV INLOW, A Initialize FIFO pointers.
MOV INMID,A
MOV INHI,A
MOV OUTLOW,A
MOV OUTMID,A
MOV OUTHI,A
February 1989 3-18

;Initialize interrupt priority register so that DRAM refresh

(TFO) gets high priority, input port service (lEO) and output
port acknowledge service get lower priority. All other
interrupts set to lower priority level.
MOV IE,#OOOOOlllb TimerO, INTO, and INTI enabled.

MOV IP,#OOOOOOlOb TimerO high priority.
MOV TLO,#TlMELO
MOV THO,#TlMEHI
MOV TMOD,#OOOOOOOlb Operate TimerO in mode 1.
MOV TCON,#OOOlOlOlb TimerO run, 10 and II ~ edge.
Initialize Port 6 Control and Status Register.

- 'BFLAG' mode set to output value of IBF
(input port BUSY signal: IBUSY)
'AFLAG' set as logic 1 output
(output port strobe signal : OSTB)
'IDS' active on negative level
(input port strobe signal : ISTB)
MOV CSR, #lOOlllOOb

MOV A,P6 Dummy read of P6 to clear IBF (IBUSY).
SETB EA Enable interrupts.
i***************************************************** ***********************
Main Routine:
Executes while not performing DRAM refresh or servicing
input port interrupt.
Check if buffer is not empty by comparing input and output

pointers. If not empty, go to NOTMT to output a byte.
MAINLP: MOV A, INLOW Compare pointers.

CJNE A,OUTLOW,NOTMT
MOV A,INMID
CJNE A, OUTMID,NOTMT
MOV A,INHI
CJNE A,OUTHI,NOTMT
SJMP MAINLP
Buffer is not empty: compute row & column addresses for

a read cycle from DRAM.
NOTMT: MOV R4,OUTLOW Save low byte of row.

MOV RS,OUTMID Save upper bit of row.
MOV A,OUTHI Shift to align correctly.
RRC A
MOV R7,A Save upper column bit.
MOV A,OUTMID Get low byte of column.
RRC A Shift in bit from OUTHI.
MOV R6,A Save.
Now do actual DRAM access to get the data byte at computed

address. Disable interrupts so we don't lose what we put
out on the ports.
February 1989 3-19

CLR EA Disable interrupts.

MOV Pl,R4 Low byte row address.
MOV A,RS Get high byte row address.
ORL A,#OFEh Make sure OBUSY stays high.
MOV P4,A
CLR RAS lRAS low.
MOV PI,R6 Low byte column address.
MOV A,R7 High byte column address.
MOV P4,A
CLR CAS ICAS low.
MOV R4,PS Get the data byte
SETB CAS ICAS high.

SETB RAS lRAS high.
CLR FOACK Clear acknowledge flag.
SETB EA Re-enable interrupts.
PLOOPI: JB OBUSY,PLOOPI Loop if printer busy.

MOV P6,R4 Move byte to output port.
CLR MAO Assert output port strobe.
NOP Kill some time.
NOP
NOP
SETB MAO De-assert output port strobe.
Following waits for lACK to occur on output port. Loops on

acknowledge flag which is set by INTI service routine when
lACK occurs.
PLOOP2: JNB FOACK,PLOOP2 Wait till lACK occurs.
INC OUTLOW Increment output buffer pointer.

MOV A,OUTLOW
CJNE A,#OO,PDONE
INC OUTMID
MOV A,OUTMID
CJNE A,#OO,PDONE
MOV A,OUTHI
INC A
ANL A,#03h Eliminate unused address bits
MOV OUTHI,A and save.
Check if input port busy flag was left asserted, indicating that
the buffer was full after last input. If so, acknowledge input
port and de-assert input busy signal.
PDONE: JNB IBF,MAINLP Not busy, return to main loop.

CLR lACK Assert IlACK.
NOP Wait 7 microseconds.
NOP
NOP
NOP
NOP
February 1989 3-20

NOP
NOP
MOV A,P6 Dummy read of P6 clears IBF (IBUSY).
NOP Wait 5 microseconds.
NOP
NOP
NOP
NOP
SETB lACK De-assert IIACK.
AJMP MAINLP Return to main loop.
;****************************************************************************
Interrupt 1 Service Routine:
- Called when output port asserts lACK.

- Sets FOACK flag and returns.
OPACK: SETB FOACK

RETI
i***************************************************** ***********************
DRAM Refresh (TimerO) Interrupt Service:
- Called once every millisecond by timer interrupt.

- Refreshes 64 rows and then returns.
- Therefore refreshes all rows every 4 milliseconds.
(Note that 41256/5lC256 DRAM only requires a 256 row refresh.)
REFRESH: PUSH PSW

MOV THO,#TlMEHI Reload timer registers.
MOV TLO,#TlMELO
MOV PI,REFCNT Get next row to refresh.

MOVX @RO,A Pulse lRAS (/WR).
INC PI
MOVX @RO,A I
INC Pl
MOVX @RO,A 2
INC Pl
MOVX @RO,A 3
INC Pl
MOVX @RO,A 4
INC Pl
MOVX @RO,A 5
INC PI
MOVX @RO,A 6
INC PI
MOVX @RO,A 7
INC Pl
MOVX @RO,A 8
INC Pl
MOVX @RO,A 9
INC Pl
MOVX @RO,A 10
INC Pl
MOVX @RO,A 11
INC PI
February 1989 3-21

MOVX @Ro,A 12
INC PI
MOVX @RO,A 13
INC PI
MOVX @RO,A 14
INC PI
MOVX @RO,A 15
INC PI
MOVX @RO,A 16
INC PI
MOVX @RO,A 17
INC PI
MOVX @RO,A 18
INC PI
MOVX @RO,A 19
INC PI
MOVX @RO,A 20
INC PI
MOVX @RO,A 21
INC PI
MOVX @RO,A 22
INC PI
MOVX @RO,A 23
INC PI
MOVX @RO,A 24
INC PI
MOVX @RO,A 25
INC PI
MOVX @RO,A 26
INC PI
MOVX @RO,A 27
INC PI
MOVX @RO,A 28
INC PI
MOVX @RO,A 29
INC PI
MOVX @RO,A 30
INC PI
MOVX @RO,A 31
INC PI
MOVX @RO,A 32
INC PI
MOVX @RO,A 33
INC PI
MOVX @RO,A 34
INC PI
MOVX @RO,A 35
INC PI
MOVX @RO,A 36
INC PI
MOVX @RO,A 37
INC PI
MOVX @RO,A 38
INC PI
MOVX @RO,A 39
INC PI
MOVX @RO,A 40
INC PI
MOVX @RO,A 41
INC PI
February 1989 3-22

MOVX @Ro,A 42
INC Pl
MOVX @RO,A 43
INC Pl
MOVX @RO,A 44
INC Pl
MOVX @RO,A 45
INC Pl
MOVX @RO,A 46
INC Pl
MOVX @RO,A 47
INC Pl
MOVX @RO,A 48
INC Pl
MOVX @RO,A 49
INC Pl
MOVX @RO,A 50
INC Pl
MOVX @RO,A 5l
INC Pl
MOVX @RO,A 52
INC Pl
MOVX @RO,A 53
INC Pl
MOVX @RO,A 54
INC Pl
MOVX @RO,A 55
INC Pl
MOVX @R0,A 56
INC Pl
MOVX @RO,A 57
INC Pl
MOVX @RO,A 58
INC PI
MOVX @R0,A 59
INC Pl
MOVX @RO,A 60
INC PI
MOVX @RO,A 6l
INC Pl
MOVX @RO,A 62
INC Pl
MOVX @RO,A 63
INC Pl Adjust for next time

MOV REFCNT,PI and save.
POP PSW
RETI
i***************************************************** ***********************
Data at Input Port:
This routine is called via interrupt INTO whenever data

is strobed into the input port. It saves the data into the
DRAM array and increments the input pointer. If the output
pointer is now equal to the input pointer, then the buffer
is full, and we leave the busy flag set so that no more
data can be input until some is output and the buffer is
no longer full.
February 1989 3-23

INDATA: PUSH PSW

PUSH ACC
MOV RI,INLOW Lower 8 bits of row to RI.
MOV R2,INMID Upper bit of row to R2.
MOV A, INRI Get upper 2 bits.
RRC A LSB to carry.
MOV RO,A
MOV A,INMID
RRC A Shift bit into MSB.
MOV R3,A Save.

MOV PI,RI LSB row address.
MOV A,R2 MSB row address.
MOV P4,A MSB row address.
STBLP: JNB ISTB,STBLP Check for end of strobe before DRAM write.
CLR RAS /RAS low.
CLR DRAMWR /WR low.
MOV PI,R3 LSB column address.
MOV A,RO MSB column address.
MOV P4,A MSB column address.
MOVX A,@RO Pulse /CAS low.
SETB RAS /RAS high.
SETB DRAMWR /WR high.
INC INLOW Increment input buffer pointer.

MOV A, INLOW
CJNE A,#OO,CKFULL
INC INMID
MOV A, INMID
CJNE A,#OO,CKFULL
MOV A,INHI
INC A
ANL A,#03h Eliminate unused address bits.
MOV INHI,A
Compare input pointer to output pointer to see if the buffer is full.
CKFULL: MOV A, INLOW

CJNE A,OUTLOW,INCLR
MOV A,INMID
CJNE A,OUTMID,INCLR
MOV A, INRI
CJNE A, OUTHI, INCLR
If we get here, the buffer is full, so skip the acknowledge pulse.
SJMP INDONE
Send acknowledge pulse on /IACK line for 7 microseconds,

de-assert input BUSY signal halfway through.
INCLR: CLR EA Disable interrupts.

CLR lACK Assert /IACK.
February 1989 3-24

NOP wait 7 microseconds.

NOP
NOP
NOP
NOP
NOP
NOP
MOV A,P6 Dummy read of P6 clears lBF (IBUSY).
NOP Wait 5 microseconds before clearing flACK.
lNDONE: POP ACC
pOP psw
SETB lACK De-assert flACK.
RETl
END
February 1989 3-25

Signefics AN418
Counter/Timer 2
of the 83C552
Application Note
Introduction to the 83C552 16-Bit Counter Timer high transition and the prescaler is in-
The 83C552 is an 80C51 derivative with The description of Counter Timer 2 in the cremented. The prescaler is incremented
several extended features: 8k RO M, 256 following paragraphs is intended to be a in the second cycle after the cycle in
bytes RAM, 10-bit A/D converter, two general overview. Details on archi- which the transition was detected. If the
PWM channels, two serial I/O channels, tecture, address locations, interrupt transition is detected before S2P1 is fin-
six 8-bit I/O ports, and four counter tim- structure and timer operation are given ished, the prescalar is incremented in the
ers. The architecture of the 83C552 is in the 83C552 Users Manual. This users next cycle. This timing is shown in Fig-
identical to that of the 80C51 making the manual may be useful to complement the ure 2. Note that this sampling rate is
two devices fully code compatible. The material presented in this application twice that of the normal 80C51 timers,
additional peripheral functions are added note. References to registers, bits, I/O TO and T1, therefore T2 has twice the
to the 80C51 Special Function Register ports and on-chip hardware will relate maximum external counting rate as com-
space and the interrupt structure is modi- directly to 83C552 Users Manual nomen- pared to the standard timers.
fied accordingly. This information is de- clature. This application note will focus
tailed in other references on the 83C552. on the use of Counter Timer 2 as a pow- Any programming of the clock source or
The focus of this application note is on erful input capture and high speed out- the prescalar divide ratio results in a
one of the timers of the 83C552, Counter put facilitator through some specific ex- reset of the prescaler. This allows the
TImer 2. amples and not on the detailed coding. state of the timer subsystem to be in a
known state upon programming. The
This counter timer includes capture, The counter timer consists of a 16-bit main 16-bit timer can not be reset by
compare and high speed output capabili- counter which is readable by software software but it is reset by activating the
ties which facilitate many control orient- through special function registers TM2L reset pin or using the external reset,
ed tasks. The objective of this note is to and TM2H. The timer itself has two RT2. The external reset, RT2 can be en-
make users of the 83C552 aware of this overflow flags, one after the entire 16-bit abled or disabled by bit T2ER in
counter timer subsystem and assist the counter and one attached to the eighth TM2CON. These resets reset the pre-
use of this subsystem by a detailed ex- stage. This latter flag reflects an over- scalar as well as the 16-bit counter.
planation of its operation supported by flow from the first byte of the counter.
actual application examples. These two flags are present in register Only one interrupt is available from the
TM21R and are labeled T2BO for the 16-bit counter timer. Two bits in
Timer 2 of the 83C552 overflow from the first byte and T20V for TM2CON control whether TM2L, TM2H,
Timer 2 of the 83C552 is in fact a timing the overflow from the entire 16-bits. or both flags will be used to generate the
controller and has an associated pro- These flags may be used to generate an interrupt. A selection for no interrupt is
grammable array. The Timer 2 subsystem interrupt. also possible.
consists of three parts:
The counter timer is controlled directly Capture System
1. the time base consists of a 16-bit through the special function register The capture system is a powerful tool to
timer with a 3-bit prescalar. The TM2CON, the timer 2 control register. measure the width of pulses or repeti-
master clock for the subsystem can This register also contains certain status tion rates. There are four independent
be derived from the on-chip oscillator flags. inputs for the signals to be analyzed,
(fose) or an external input, T2. It has CTIO through CTI3. These inputs are al-
an external reset, RT2, by which a The prescaler divides the input clock by ternate functions to Port 1. Each input is
signal applied to this input can reset a progammable ratio. The prescaler di- connected to a dedicated capture regis-
the timer if the external reset is vide value is progammable to divide by ter. A transition at any of these inputs
enabled. 1, 2, 4, or 8 as controlled by T2PO and will cause the content of the 16-bit
2. a capture system consisting of four T2P1 in TM2CON. counter timer to be loaded into the re-
capture registers and four capture spective capture register. The capture
inputs which can be used for a wide The input clock to the prescalar is either can occur upon various conditions of the
variety of time measurements on ex- fosc / 12 or the external input, T2. The input signal as specified by certain bits in
ternal signals. clock input to the prescaler may also be the capture control register, CTCON.
3. a compare system consisting of three shut off. This clock input selection is Each input can be set to cause a cap-
compare registers and eight associ- controlled by bits T2MSO and T2MS1 in ture on a low to high tranSition, a high to
ated high-speed outputs which can TM2CON. low transition, or on both transitions. Up-
be activated upon a match between on a capture taking place, each input
the 16-blt timer and one of the com- If T2 is used as the input clock to the causes an interrupt flag to be set in the
pare registers. timer 2 subsystem, the hardware logic Timer 2 Interrupt Flag Register, TM21R.
samples this input and looks for a low to If enabled an interrupt will be genera-
For reference a complete block diagram high transition. If the logic detects a log-
ted.
of the 83C552 Counter Timer 2 subsys- ic 0 at the T2 input in state S2P1 of the
tem is shown in Figure 1. microcontroller and a logic 1 in state
S5P1, then this is recognized as a low to
February 1989 3-26

Counter Timer 2 S83C552
off
6 8~bit
f---
overflow
~I PRESCALER T2 COUNTER
interrupt
I
16-bit overflow
interrupt
T2
.? J
RT2
T2ER
------<Of
external reset
enable
S R P4.0
S R P4.1
INT
S R P4.2
I/O port 4
S R P4.3~
S R P4.4 "r-Y
S R P4.5
TG T P4.6
TG T P4.7
STE RTE
S = set T2 SFR address: TML2 = lower 8 bits

R = reset TMH2 z higher 8 bits
T = toggle
TG = toggle status
Figure 1. 83C552 Counter Timer 2 Block Diagram
One of the capture inputs is shown in end of this machine cycle. The interrupt which shows the compare system for
more detail in Figure 3. All of the other flag CTIO is also set. P4.S (a set - reset high speed output)
capture inputs are similar to this one. and P4.6 (a toggle high speed output).
The capture input is gated with the cap- Compare System
ture enable bits CTNO and CTPO which The compare system of Timer 2 can be There are two compare registers associ-
are located in CTCON. According to the used to generate a set of outputs whose ated with the set - reset outputs.
status of these bits, the desired edges transitions are controlled directly by the These registers are CMO and CMt. In
are selected to generate the capture en- time defined by the 16-bit counter timer. addition there are two enable registers:
able pulse. The input pulse transient de- There are eight of these high speed out- one to enable setting of an output and
tection is at the input of the enable pulse puts which are directly controlled from the other to enable resetting of an out-
generator. The input signal is sampled at Counter Timer 2. These outputs are al- put. These registers are STE and RTE
SI PI of the machine cycle. If a logic 1 ternate functions to Port 4. Six of these respectively. The content of CMO and
is detected when a logic 0 was detected outputs are set - reset controlled CM 1 are continuously compared to the
at the same time in the previous cycle, (CMSRO through CMSRS) and two are content of the 16-bit counter. Whenever
then the event is taken as a transition. toggle controlled (CMTO and CMT1). To there is a match between the 16-bit
An enable pulse is sent to the capture clarify the operation, these two types counter and the contents of CMO, a SET
register and the contents of timer 2 is will be discussed separately. I n the fol- pulse is generated. Similarly, whenever
copied into the capture register at the lowing discussions, refer to Figure 4 there is a match between the timer and
February 1989 3-27

1 machine cycle
The basic microcontroller

instruction cycle timing
by transition 1 by transition 2
Counter
incremented
Figure 2. The Sampling of the External Clock Signal
TM2 CTa
TM2H
TM2L
internal
bus
TM21R
~JlJ enable
CTOI pulse I
I
it
CTCON
~--~---+~ CTNO aMble. capture

on ..lIIno odoo
CTPO ...ute. captura

on relaln; edg.
S1P1J-LJL ________..J
I 1M i
Figure 3. Capture Subsystem for CTOI
February 1989 3-28

TM21R
eMI
2
to
eMI Interrupt
t }
system
eMI
o
I- - - - 'i
Port P4
r---I
! !
P4.S
P4.6
P4.7
control
Toggle FF
: STE
!
STE.6
STE.7
Figure 4. Compare System for P4.5 and P4.6

the contents of CM1, a RESET pulse is The two toggle controlled outputs are Application Example
generated. The set pulse is applied to CMTO and CMT1 and these are associ- Timed Fuel Injection
the set - reset outputs, CMSRO through ated with compare register CM2. These In modern automobiles, optimal combus-
CMSR5, through gates controlled by bits outputs are also alternate functions on tion is necessary to meet emission stan-
in STE. Bits 0 through 5 in STE control Port 4. Upon a compare between the dards and improve fuel consumption.
the application of the SET pulse to one counter and the contents of CM2, CM2 Optimal combustion depends on several
of the high speed outputs. For example generates a toggle pulse which is applied factors and is enhanced by proper fuel
STE.O controls the gating of the SET to the high speed outputs CMTO and injection based upon these factors
pulse to CMSRO, STE.1 controls the CMT1 through a set of gates. The gates which vary according to engine speed
gating of the SET pulse to CMSR1 and control the application of the toggle and other factors. Thus the task is to
so forth. Thus if the corresponding SET pulse to the toggle outputs as specified control the opening and clOSing of the
enable bit in STE is a 1 and a compare by the high order bits of register RTE. engine fuel injectors of each cylinder
occurs with CMO, then that high speed RTE.6 controls CMTO and RTE.7 controls relative to the crankshaft reference
output will become set. Similarly, the re- CMT1. Should the corresponding bit of pOint.
set pulse from CM1 is applied to the high RTE be set, then the toggle pulse is en-
speed outputs CMSRO through CMSR5 abled to the associated high speed out- For the application example here, we
through gates controlled by bits in RTE. put and that output will toggle upon will not consider the factors which de-
As with STE, bits 0 through 5 in RTE generation of the toggle pulse from CM2. termine the timing relationships. These
control the application of the reset pulse The structure of these toggled outputs is are assumed to be given quantities. The
to one of the high speed outputs. If a different from the other high speed out- example here will focus upon the imple-
compare occurs between the timer and puts in that the toggling is actually ac- mentation of the injector timing control
CM 1, a high speed output will be reset complished in a separate toggled flip flop signals and how they are generated us-
if its corresponding enable bit in RTE is a and not directly in the port latch. This ing the Counter Timer 2 system. The il-
1. Compares with CMO and CM1 set in- toggle flip flop can not be controlled lustration considers a four cylinder en-
terrupt flags which, if enabled, can be directly by software and powers up in an gine. While this is an automotive applica-
used to generate an interrupt. indeterminate state. The state of the tion which serves to clearly illustrate
toggle flip flops is readable in STE bits 6 Counter Timer 2 Subsystem operation, it
and 7. is clear that many systems share similar
February 1989 3-29


timing requirements and the techniques lute reference for all real time output op- tor from the required angle at which the
employed here are applicable to a wide erations. This time is available in capture injector is to open. This time is made
class of timing tasks. The 83C552 will register CTO. Note that at 12 MHz available for the interrupt service routine
also support six cylinder engine control. operation, Timer 2 can have a resolution which responds to a compare from CMO.
as fine as 1 microsecond with a total The interrupt service routine is exited.
Figure 5 shows the injection timing re- time before overflow of over 65 millisec-
quired for two consecutive revolutions of onds and these times are adjustable by The next interrupt to occur per the Fig-
the engine crankshaft. Start and stop of increasing the prescalar divide ratio. A ure for this example is a result of a
the injection are given relative to a ref- proper selection can make the timing compare with CM 1 which will be a result
erence paint on the crankshaft. The cyl- calculations relatively simple. Second, at of the injector stop time for cylinder 4
inders are numbered in the order of the the time the input is captured, flags having been reached. The flags in an
injection sequence (not with reference to which keep track of the phases of the internal status register are employed to
their physical location). Start of the in- crankshaft cycle are reset when cylin- keep track of the cylinder number that is
jection is usually given in angular meas- der 1 is at top dead center. These flags presently active for both injection stop
ure with respect to top dead center and are used in the interrupt service routines and injection start times. After identifying
the injection duration is assumed to be a to tell which action is required for that this interrupt from the flags, the proces-
time value calculated from engine envi- phase of the crankshaft. sor uses the injector start time for cylin-
ronmental factors and operating parame- der 1 (previously loaded into CMO) and
ters. The angle for the start of the injec- ConSider now the sequence of events in the predetermined duration to calculate
tion must be converted into time with one rotation of the engine crankshaft the injector stop time for cylinder 1.
respect to the reference point. and refer to Figure 5 during the discus- This value is loaded into compare regis-
sion. Assume that the engine is running, ter CM 1 and the reset enable bit for high
The injector drivers are assumed to be that all relevant parameters are available speed output CMSRO is programmed to a
connected to the Port 4 high speed and that it has been determined that the 1. This is bit RTE.O the reset enable bit
outputs CMSRO through CMSR3. To ob- processor is responding to the interrupt for the cylinder 4 injector is set to a (bit
tain the top dead center reference point, associated with the top dead center cap- RTE.3). The interrupt routine is now
the signal from the appropriate sensor is ture, CTO!. Interrupts for CTOI, CMO exited.
connected to the capture input CTO!. (compare register 0), and CM1 (compare
The interrupt for this capture input is en- register 1) are enabled. Upon entering The next interrupt to occur will be for
abled so that software can synchronize the interrupt service routine for CTOI, the the start time for the injector for cylinder
its operation to this time reference and previous value of the captured top dead 2. This and all subsequent cases follow
make use of the top dead center time in center time is subtracted from the the same sequence of events as for the
the injector timing calculations. The present value and the crankshaft rota- cylinder 1 CMO interrupt described a-
software synchronization takes two tion time is determined. This is used to bove. In this case calculations are made
forms. First the captured time is an abso- compute the time to open the first injec- for cylinder 2 and loaded into CMO,
Reference
I J J
T-stop
<:----------------------->
T-start
Cyl 1
<----->1 . . . . Jnj.~9:H?n•.•
Cyl 2
Cyl 3
Cyl 4
Shaded areas indicate injectors are on.

Figure 5. Four Cylinder Injection Timing
February 1989 3-30

STE.1 is programmed to a 1 and STE. 0 As an example consider the interrupt Application Example -
is programmed to a O. Similarly, the next service routine for CMO. Upon entering Timed Ignition
interrupt for CM1 is treated in the same the routine, all interrupts are disabled. In electronic ignition systems, multiple
way and the sequence of events rotates Then the following actions are ignition coils may be used and each coil
around through all cylinders in turn. The performed: is fired by electronic means rather than
flag bits associated with this operation with the old stile mechanical breakers.
keep track of the injector sequencing. - set bit in STE to start next injector In a four cylinder engine, there may be
- clear bit in STE for injector just started two ingnition coils, one coil providing
While this example shows the injection - load CMO with start time for next spark for a pair of cylinders. Both plugs
stop time of one cylinder overlapping in- injector fire at the same time. For one cylinder,
to the injector on time of the subsequent - clear CMIO interrupt flag in TM21R the spark occurs at the appropriate time
cylinder, close examination of the opera- while for the other cylinder, the spark
tions described above reveal that the Now that the essential set up is made for
occurs at the end of the exhaust stroke
start and stop events are independent the next interrupt, all interrupts are now and has no effect. With timing referenc-
and can overlap or not as required. In enabled. However the return to the main
es to crankshaft top dead center provid-
this way all injectors may be driven in- program is not invoked until the following ed by an external sensor, the ignition
dependently and have overlapping on ancillary processing is completed:
timing for the engine may be generated
times. in the 83C552 and applied to the elec-
- calculate the next absolute start time tronic drivers for the ignition coils.
Given that this is an example applicable
to general usage, it is possible that infor the next injector (the next load
value for CMO) To illustrate the toggle high speed out-
terrupt service routine could be relatively puts of the 83C552 Counter Timer 2
long as it would be in an actual injector subsystem, the following example will
- increment the flag so that the next
application. Since the service routine discuss the ignition timing in a four cylin-
entry to this interrupt service routine
has other interrupts disabled, the length der engine employing the two coil ap-
will be able to identify the next injec-
may cause real time conflicts. To elimi- proach with one coil for a pair of cylin-
tor to start.
nate this potential problem, the interrupt ders. The coil timing is illustrated in Fig-
service routines are divided into two The process performing these calcula- ure 6. A reference time is used which is
parts. I n the first part, all other interrupts tions can be interrupted to service real a given interval prior to top dead center
are disabled and the essential register time functions. so that the times used in the illustration
loading is done to prepare for the next can be always after the reference.
interrupt. After this is completed, all in- There are two times of interest for each
terrupts are enabled and the ancillary coil: the load time and the ignition point.
service routine functions are performed
prior to a return to the main routine.
Reference TDC
I II
Coil 1
-----~.-
Coil 2
Figure 6. Four Cylinder, Two Coil Ignition Timing
February 1989 3-31


Ignition advance is usually given in de- Upon entering the interrupt service rou- Conclusion
grees crankshaft angle prior to top dead tine, other interrupts are disabled. Exam- This application note has examined one
center. As with injection, this angle is ination of the flags reveals that the state aspect of the 83C552 CMOS 80C51 de-
assumed to be derived from other calcu- of the ignition sequence is that Coil 1 rivative microcontroller. The Counter
lations and is a given value for this illus- has been turned on to begin the current Timer 2 Subsystem has been applied to
tration. This angle must be converted in- build up (load time). The next event will a complex timing task of gasoline engine
to a time with respect to the reference therefore be turning off Coil 2 to cause injector valve and ignition coil timing
point. The load time (the time at which ignition. The interrupt service routine control. While this is a specific applica-
the coil has to be switched on to reach then performs the following actions: The tion to the automotive interests, the re-
the current that will give sufficient en- time to turn off Coil 2 is moved into sult are applicable to a wide variety of
ergy for an adequate spark) must be compare register 2, CM2. Bit 6 of RTE time measurement and control applica-
subtracted from the desired ignition is cleared; this disconnects the output of tions. The 83C552 would be ideal for
point. At the ignition time, the coil will be CM2 from the toggle flip flop of P4.6 many electromechanical systems such as
switched off and the spark will be (Coil 1). Bit 7 of RTE is set; this con- copy machines, fax machines, industrial
generated. nects the output of CM2 to the toggle process control equipment, automatic
flip flop of P4.7 (Coil 2). The flags are transmission control, and anti-5kid and
The coil driver electronics are connected incremented to indicate that the next in- anti-lock braking control.
to port bits P4.6 and P4.7. Ignition Coil terrupt will be a result of Coil 2 turning
1 is connected to P4.6 and ignition Coil off and causing ignition. The other inter- These application areas are those which
2 is connected to P4.7. These outputs rupts can be enabled and a return to the can successfully employ the 83C552
are the toggle high speed outputs con- main program can be executed. After Counter Timer 2, however the other fea-
trolled by the 16-bit compare register, the other interrupts are enabled and be- tures should not be overlooked. When
CM2. The program simply needs to set fore a return is made to the main pro- combined with the 10-bit A to 0 Con-
up the compare and control registers to gram, it may be convenient to do any verter, the Pulse Width Modulator, the
turn the coils on and off at the appropri- necessary calculations to determine the 12C serial bus and peripheral device fam-
ate times. It is assumed in this example time value to be loaded into CM2 in the ily, the 83C552 provides minimum com-
that the ignition and load times are given next CM2 interrupt. ponent count solutions for cellular radio
quantities and have been determined systems, professional audio systems, and
previously. Since the flip flops are toggled, it is like- medical instrumentation products such as
ly that upon power up of the micro- bed side patient monitors and analyzers
Consider now the sequence of events in controller, the toggle flip flops will not be for home care and sports use.
two rotations of the engine crankshaft in the desired state. To get the toggle
and refer to Figure 6. Assume that the flip flops in the correct state in the igni-
engine is running, that all relevant pa- tion cycle, the flip flops must be toggled
rameters are available and that it has if they are in the wrong state. To deter-
been determined that the processor is mine if this is necessary, the state of
responding to the interrupt associated the toggle flip flops can be read from the
with a compare to CM2. The top dead STE register. The state of the P4.6 flip
center time and crankshaft rotation flop is present in STE bit 6 and the state
speed have been already determined of the P4.7 flip flop is present in STE bit
through the top dead center capture, 7. Comparing the actual state to the re-
CTOI. This is the same as in the injector quired state determines which if any or
example. The interrupt for CTOI is ena- both of the flip flops must be toggled. If
bled. From the top dead center time, the a toggle is necessary to put one or both
times to turn on and turn off the coil of the flip flops in the correct state, the
drivers are computed and made available corresponding bits in RTE would be set
in data storage locations in the micro- for those flip flops requiring the toggle
controller. It is also convenient to have and CM2 would be loaded with a value
flags to identify the step in the complete that is slightly larger than the present
ignition cycle. The flags are cleared in contents of Timer 2. If desired for relia-
the interrupt service routine for top dead bility purposes, the state of the flip flops
center of cylinder 1. could be checked periodically against
the ignition cycle flags to determine if a
correction is necessary.
February 1989 3-32

Signetics AN420
Using up to 5 External
Interrupts on 8051 Family
Microcontrollers
Application Note
8051 family microcontrollers are equip- In TMOD: In TCON: In IE: SERIAL PORT CONFIGURATION
ped with up to two inputs which may be GATE - a TRi - 1 ETi - 1 The serial port can be placed in mode 2,
used as general-purpose interrupts. A CIT - 1 EA - 1 which is a 9-bit UART with the baud rate
typical device provides a total of 5 inter- M1 - 1 derived from the oscillator. The external
rupt sources. Timer a and Timer 1 gener- MO - a interrupt is signaled through this port on
ate vectored interrupts, as does the Se- the RXD receive data pin. Reception is
rial Port. Applications that require more Where "i" is the timer number being used initiated by a detected 1-to.{) transition
than two externally signaled vectored in- as the external interrupt. The TMOD val- at RxD. The signal must stay at a for at
terrupts, and do not use one or more of ue would be 66 hexadecimal if both tim- least five-eighths of a bit period for this
the counters or the serial port, can be er are being used as external interrupt level to be recognized. Refer to the de-
configured to use these facilities for ad- sources, x6 hex for timer 0, and 6x hex scription of baud rates to determine the
ditional external interrupt inputs. for timer 1. The interrupt priority may length of a bit period at the oscillator
also be set in the IP register. frequency selected for the application.
This note describes a method to config- The input signal should remain low for at
ure the timer/counters and the serial port A falling edge on the corresponding
least one bit period and for not more
for use as interrupt inputs. Minimum re- TimerO or Timer1 input (TO or T1) will
than 9 bit periods.
sponse time is a goal for this config- cause the counter to overflow and gen-
uration. erate a timer interrupt. The counter will To prepare the serial port for use as an
be automatically loaded with another F F external interrupt, the following bits must
Another popular method to implement from the reload register, so the interrupt be set up:
extra interrupt inputs is to poll under can occur again as soon as the interrupt
software control a port pin configured as service routine completes. Counter/Timer In SCON:
an input. This method is necessary when operation is described in detail in else- SMa - 1
the on-<:hip peripherals are in use. Appli- where in this manual. SM1 - a
cations where this approach is recom- SM2 - a
mended are ones in which the processor REN - 1
spends more than half of the time exe-
cuting a "wait loop", or a short code
sequence which jumps or branches back
on itself without performing any func-
tions. I n this case, the instructions that
will check the state of input used as an Xl 80eS1
interrupt source are inserted into this se-
quence. Consequently, this input is ig- Port 0
nored when other routines are being ex- X2
ecuted. This input may have to be
Port 1
latched externally, or the processor may
miss the signal while executing other RESET
routines. Port 2
EA
Dedicated interrupt inputs that vector
the processor to individual service rou- INTO (P3.2l
tines (as the two general purpose inter-
P3.l
rupt inputs work) do not have the draw-
backs of the method described above.
INTl (P3.3l P3.6
COUNTERfTlMER CONFIGURATION TO (P3.4l P3.7
Timers a and 1 are placed in Mode 2,
which configures the timer register as an
8-bit counter with automatic reload. The Ext. Interrupt T1 (P3.Sl
counter and reload register are loaded
with FF hexadecimal which is stored in Ext. Interrupt RXD (P3.0l
TH 1 and TL 1 or THO and TLO.
To prepare one of the timers for this kind

of operation, a number of control bits
have to be set up. The following is a list Figure 1. SOC51 Five Interrupt Configuration
of these bits and their values:
February 1989 3-33

Using up to 5 External Interrupts 8051 Family
The Serial Port I nterrupt is then used as Note that the response time for this input
a general purpose interrupt. The con- will be slower than for the Counter/Timer
tents of receive buffer should be ig- inputs. This is due to the fact that the RI
nored, and will subsequently be overwrit- is generated after the eighth serial data
ten during the next interrupt. bit time after the falling edge on RxD.
; Demonstration program for five external interrupts.

$MOD5l
$TITLE (Five vectored External Interrupts)
Interrupt Jump Table
ORG OH ;Reset
AJMP setup
ORG 3H ;External interrupt O.
RETI ;(not implemented in this demo)
ORG OBH ;Timer a interrupt.
AJMP TimO
ORG l3H ;External interrupt 1.
RETI ;(not implemented in this demo)
ORG lBH ;Timer 1 interrupt.
AJMP Timl
ORG 23H ;Serial port interrupt.
AJMP Serial
Begin setup code
Setup MOV SP,#7FH ;Initialize the stack pointer.
Configure both timers
MOV TMOD,#66H ;Put both counters into mode 2.
MOV A,#OFFH
MOV TLO,A ;Load FF hex into both counters
MOV THO,A
MOV TLl,A
MOV THl,A
SETB ETa ; Enable Timer a interrupt.
SETB ETI ;Enable Timer 1 interrupt.
SETB TRO ; Enable Timer a to run.
SETB TRI ; Enable Timer 1 to run.
Configure the serial port
SETB ES ;Enable serial port interrupt.
MOV SCON,#90H ;Put the serial port in mode 2.
SETB EA ;Enable interrupt system.
Wait: NOP ;Wait for an interrupt.
JMP Wait
Serial:NOP ;Serial interrupt service routine.
CLR RI ;Clear receiver interrupt flag.
RETI
TimO: NOP ;Timer a interrupt service routine.
RETI
Timl: NOP ;Timer a interrupt service routine.
RETI
END
February 1989 3-34

Signefics Section 4
Inter-Integrated (12C)
Circuit Bus
INDEX
12C Bus Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 4-1
12C Peripheral Selection Guide ............................... 4-13
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Signetics 12C Bus
Specification
Linear Products
INTRODUCTION a receiver, while a memory can both receive - microcomputer A (master) addresses
For 8-bit applications, such as those requiring and transmit data. In addition to transmitters microcomputer B (slave)
single-chip microcomputers, certain design and receivers, devices can also be consid- - microcomputer A (master receiver)
criteria can be established: ered as masters or slaves when performing receives data from microcomputer B
• A complete system usually consists data transfers (see Table 1). A master is the (slave transmitter)
of at least one microcomputer and device which initiates a data transfer on the - microcomputer A terminates the
other peripheral devices, such as bus and generates the clock signals to permit transfer.
memories and 1/0 expanders. that transfer. At that time, any device ad-
dressed is considered a slave. Even in this case, the master (microcomputer
• The cost of connecting the various
A) generates the timing and terminates the
devices within the system must be The 12 C bus is a multi-master bus. This means
transfer.
kept to a minimum, that more than one device capable of control-
• Such a system usually performs a ling the bus can be connected to it. As The possibility of more than one microcompu-
control function and does not require masters are usually microcomputers, let's ter being connected to the 12 C bus means
high-speed data transfer. consider the case of a data transfer between that more than one master could try to initiate
• Overall efficiency depends on the two microcomputers connected to the 12C a data transfer at the same time. To avoid the
bus (Figure 1). This highlights the master- chaos that might ensue from such an event,
devices chosen and the
slave and receiver-transmitter relationships to an arbitration procedure has been developed.
interconnecting bus structure.
be found on the 12 C bus. It should be noted This procedure relies on the wired-AND con-
In order to produce a system to satisfy these that these relationships are not permanent, nection of all devices to the 12C bus.
criteria, a serial bus structure is needed. but only depend on the direction of data If two or more masters try to put information
Although serial buses don't have the through- transfer at that time. The transfer of data
put capability of parallel buses, they do reon to the bus, the first to produce a one when
would follow in this way: the other produces a zero will lose the
quire less wiring and fewer connecting pins.
1) Suppose microcomputer A wants to send arbitration. The clock signals during arbitra-
However, a bus is not merely an interconnect-
information to microcomputer B tion are a synchronized combination of the
ing wire, it embodies all the formats and
- microcomputer A (master) addresses clocks generated by the masters using the
procedures for communication within the sys-
microcomputer B (slave) wired-AND connection to the SCL line (for
tem.
more detailed information concerning arbitra-
- microcomputer A (master transmitter)
Devices communicating with each other on a tion see Arbitration and Clock Generation).
serial bus must have some form of protocol sends data to microcomputer B (slave
receiver) Generation of clock Signals on the 12C bus is
which avoids all possibilities of confusion,
data loss and blockage of information. Fast - microcomputer A terminates the always the responsibility of master devices;
devices must be able to communicate with transfer. each master generates its own clock signals
when transferring data on the bus. Bus clock
slow devices. The system must not be depen- 2) If microcomputer A wants to receive infor- signals from a master can only be altered
dent on the devices connected to it, other- mation from microcomputer B when they are stretched by a slow slave
wise modifications or improvements would be
impossible. A procedure has also to be re-
solved to decide which device will be in
control of the bus and when. And if different
devices with different clock speeds are con-
nected to the bus, the bus clock source must
be defined.
All these criteria are involved in the specifica-
tion of the 12C bus.
THE 12C BUS CONCEPT

Any manufacturing process (NMOS, CMOS,
12L) can be supported by the 12C bus. Two
wires (SDA - serial data, SCL - serial clock)
carry information between the devices con-
nected to the bus. Each device is recognized
by a unique address - whether it is a micro-
computer, LCD driver, memory or keyboard
interface - and can operate as either a trans-
mitter or receiver, depending on the function
of the device. Obviously an LCD driver is only Figure 1. Typical 12C Bus Configuration
December 1988 4-1

Signetics Linear Products
12C Bus Specification
Table 1. Definition of 12C Bus Terminology device holding down the clock line or by
another master when arbitration takes place.
TERM DESCRIPTION
Transmitter The device which sends data to the bus
Receiver The device which receives data from the bus
GENERAL CHARACTERISTICS
Both SDA and SCL are bidirectional lines,
Master The device which initiates a transfer, generates clock connected to a positive supply voltage via a
signals and terminates a transfer pull·up resistor (see Figure 2). When the bus
Slave The device addressed by a master is free, both lines are High. The output stages
of devices connected to the bus must have
Multi·master More than one master can attempt to control the an open-drain or open·collector in order to
bus at the same time without corrupting the message perform the wired-AND function. Data on the
Arbitration Procedure to ensure that if more than one master 12C bus can be transferred at a rate up to
simultaneously tries to control the bus, only one is 1OOkbitls.The number of devices connected
allowed to do so and the message is not corrupted to the bus is solely dependent on the limiting
Synchronization Procedure to synchronize the clock signals of two or bus capacitance of 400pF.
more devices
BIT TRANSFER
Due to the variety of different technology
-.,....-1~--- +VDD devices (CMOS, NMOS, 12L) which can be
connected to the 12C bus, the levels of the
logical 0 (Low) and 1 (High) are not fixed and
SOA (SERIAL DATA LINE) depend on the appropriate levi'll of VDD (see'
(SERIAL CLDCK LINE) Electrical Specifications). One clock pulse is
~L~---~~----i---+----~----;--- generated for each data bit transferred.
r------ I j------ -I Data Validity
I I I I The data on the SDA line must be stable
: ~LK1_l : : SCLK2-.J : during the High period of the clock. The High
lOUT I lOUT I or Low state of the data line can only change
I I I I
I I I I when the clock signal on the SCL line is Low
: ~LK DATA : : SCLK DATA :
(Figure 3).
I IN
1________________ ...J
IN I IL _______________ ...JI
IN IN
Start and Stop Conditions
Within the procedure of the 12 C bus, unique
DEVICE 1 DEVICE 2
situations arise which are defined as start and
stop conditions (see Figure 4).
Figure 2. Connection of Devices to the 12C Bus
A High·to-Low transition of the SDA line while
SCL is High is one such unique case. This
situation indicates a start condition.
A Low·to·High transition of the SDA line while
SCL is High defines a stop condition.
Start and stop conditions are always generat·
ed by the master. The bus is considered to be
busy after the start condition. The bus is
considered to be free again a certain time
after the stop condition. This bus free situa·
tion will be described later in detail.
Detection of start and stop conditions by
Figure 3. Bit Transfer on thel 2 C Bus
devices connected to the bus is easy if they
possess the necessary interfacing hardware.
However, microcomputers with no such inter·
SDA f\l
I I
C~ ill
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SDA
face have to sample the SDA line at least
twice per clock period in order to sense the
transition.
~L -t:1'-
L~J '--I
rt~ rr-t- ~L
'--I L~J TRANSFERRING DATA
START CONDITION STOP CONDITION Byte Format
Every byte put on the SDA line must be 8 bits
Figure 4. Start and Stop Conditions long. The number of bytes that can be
transmitted per transfer is unrestricted. Each
byte must be followed by an acknowledge bit.
December 1988 4-2
r--,
~
ACKNOWLEDGEMENT I I
SIGNAL FROM RECEIVER I I
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CLOCK UNE HELDLQWWHILE
I I
INTERRUPTS ARE SERVICED I I
1 -8
'i' rt-t
~V~K'\..../ I I P
L_...l
SlOP
CONDITION
Figure 5. Data Transfer on the 12C Bus
DATA OUTPUT
BYTRANSMrlTER
f\
II \j1_
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/ ___J X "'_ _ _.....
>C~ " -_ __
/
sc~~~ I I
Is I
L..::J
srART
CONDlnoN
Figure 6. Acknowledge on the 12C Bus
Data is transferred with the most significant The receiving device has to pull down the slave leaves the data line High and the
bit (MSB) first (Figure 5). " a receiving device SDA line during the acknowledge clock pulse master generates the STOP condition.
cannot receive another complete byte of data so that the SDA line is stable Low during the
In the case of a master receiver involved in a
until it has performed some other function, for high period of this clock pulse (Figure 6). Of
transfer, it must signal an end of data to the
example, to service an internal interrupt, it course, setup and hold times must also be
slave transmitter by not generating an ac-
can hold the clock line SCL Low to force the taken into account and these will be de-
knowledge on the last byte that was clocked
transmitter into a wait state. Data transfer scribed in the Timing section.
out of the slave. The slave transmitter must
then continues when the receiver is ready for
Usually, a receiver which has been addressed release the data line to allow the master to
another byte of data and releases the clock
is obliged to generate an acknowledge after generate the STOP condition.
line SCL.
each byte has been received (except when
In some cases, it is permitted to use a the message starts with a CBUS address.
different format from the 12C bus format, such
When a slave receiver does not acknowledge
ARBITRATION AND CLOCK
as CBUS compatible devices. A message GENERATION
on the slave address, for example, because it
which starts with such an address can be
is unable to receive while it is performing Synchronization
terminated by the generation of a stop condi-
some real-time function, the data line must be All masters generate their own clock on the
tion, even during the transmission of a byte.
left High by the slave. The master can then SCL line to transfer messages on the 12C bus.
In this case, no acknowledge is generated.
generate a STOP condition to abort the Data is only valid during the clock High period
Acknowledge transfer. on the SCL line; therefore, a defined clock is
Data transfer with acknowledge is obligatory. needed if the bit-by-bit arbitration procedure
If a slave receiver does acknowledge the
The acknowledge-related clock pulse is gen- is to take place.
slave address, but some time later in the
erated by the master. The transmitting device
transfer cannot receive any more data bytes, Clock synchronization is performed using the
releases the SDA line (High) during the ac-
the master must again abort the transfer. This wired-AND connection of devices to the SCL
knowledge clock pulse.
is indicated by the slave not generating the LINE. This means that a High-to-Low transi-
acknowledge on the first byte following. The
December 1988 4-3
,2C Bus Specification
Arbitration can carry on through many bits.

START COUNTING The first stage of arbitration is the comparison
1_ WAIT -I-..!I!!HPERIOD of the address bits. If the masters are each
I STATE 1 trying to address the same device, arbitration
--""'\ continues into a comparison of the data.
ClK
1 ____-+_~ _______ J _____________+~------,~--- Because address and data information is
used on the 12C bus for the arbitration, no
information is lost during this process.
ClK A master which loses the arbitration can
2 ____ +-__ -+~,~~ ______________ _J'~~-----,--~-
generate clock pulses until the end of the
byte in which it loses the arbitration.
SCl If a master does lose arbitration during the
addressing stage, it is possible that the win-
ning master is trying to address it. Therefore,
Figure 7. Clock Synchronization During the Arbitration Procedure the losing master must switch over immedi-
ately to its slave receiver mode.
Figure 6 shows the arbitration procedure for
TRANSMITTER 1 LOSES ARBrrRATlON two masters. Of course more may be in-
DATAl + SDA
volved, depending on how many masters are
DATA
1 connected to the bus. The moment there is a
difference between the internal data level of
the master generating DATA 1 and the actual
DATA level on the SDA line, its data output is
2~.'--'~~ __~__'~____-+__~ ______~~__--f switched off, which means that a High output
level is then connected to the bus. This will
not affect the data transfer initiated by the
SDA winning master. As control of the 12 C bus is
decided solely on the address and data sent
by competing masters, there is no central
master, nor any order of priority on the bus.
SCl
Use of the Clock Synchronizing
Mechanism as a Handshake
In addition to being used during the arbitration
Figure 8. Arbitration Procedure of Two Masters procedure, the clock synchronization mecha-
nism can be used to enable receiving devices
tion on the SCL line will affect the devices state of the SCL line and all of them will start to cope with fast data transfers, either on a
concerned, causing them to start counting off counting their High periods. The first device byte or bit level.
their Low period. Once a device clock has to complete its High period will again pull the
On the byte level, a device may be able to
gone Low it will hold the SCL line in that state SCL line Low.
receive bytes of data at a fast rate, but needs
until the clock High state is reached (Figure more time to store a received byte or prepare
In this way, a synchronized SCL clock is
7). However, the Low-to-High change in this
generated for which the Low period is deter- another byte to be transmitted. Slave devices
device clock may not change the state of the can then hold the SCL line Low, after recep-
mined by the device with the longest clock
SCL line if another device tion and acknowledge of a byte, to force the
Low period while the High period on SCL is
clock is still within its Low period. Therefore,
determined by the device with the shortest master into a wait state until the slave is
SCL will be held Low by the device with the
clock High period. ready for the next byte transfer in a type of
longest Low period. Devices with shorter Low
handshake procedure.
periods enter a High wait state during this Arbitration
time. Arbitration takes place on the SDA line in On the bit level, a device such as a micro-
such a way that the master which transmits a computer without a hardware 12C interface
When all devices concerned have counted off
High level, while another master transmits a on-chip can slow down the bus clock by
their Low period, the clock line will be ie:
Low level, will switch off its DATA output extending each clock Low period. In this way,
leased and go High. There will' then be no
stage since the level on the bus does not the speed of any master is adapted to the
difference between the device clocks and the
correspond to its own level. internal operating rate of this device.
December 1966 4-4

Signetlcs Linear Products
FORMATS master still wishes to communicate on the er and the slave receiver becomes a slave r"
Data transfers follow the format shown in bus, it can generate another start condition, transmitter. This acknowledge is still generat-
Figure 9. After the start condition, a slave and address another slave without first gener- ed by the slave.
address is sent. This address is 7 bits long; ating a stop condition. Various combinations
The stop condition is generated by the mas-
the eighth bit is a data direction bit (R/W). A of read/write formats are then possible within
ter.
zero indicates a transmission (WRITE); a one such a transfer.
indicates a request for data (READ). A data During a change of direction within a transfer,
At the moment of the first acknowledge, the
transfer is always terminated by a stop condi- the start condition and the slave address are
master transmitter becomes a master receiv-
tion generated by the master. However, if a both repeated, but with the R/W bit reversed.
ri ri
SDAl'\L.r~~OOCAV!
I I I I
SCLW~~-vvvtt
L jL L - - - J L-.-J L---.J ! ! L---.J I ! L-.-J --l
START ADDRESS R/W ACK DATA ACK DATA ACK SlOP
CONDITION CONDITION
Figure 9. A Complete Data Transfer
Possible Data Transfer Formats are:
a) Master transmitter transmits to slave S SLAVE ADDRESS RtW A DATA A DATA A P

receiver. Direction is not changed.
A ~ ACKNOWLEDGE 1/
S ~ START 'O'(WRITE) DATA TRANSFERRED
P~sTOP (n BYTES + ACKNOWLEDGE)
b) Master reads slave immediately after

first byte. S SLAVE ADDRESS R/W A DATA A DATA A
II
~'(READ) DATA TRANSFERRED
(n BYTES + ACKNOWLEDGE)
c) Combined formats.
I s I SLAVEADDRESS I R/W I A I DATA I A I s I SLAVE ADDRESS I RtW I A I DATA I A I P I
J Lr~ (n BYTES
+ ACKNOWLEDGE) J lL.r~ (n BYTES
+ ACKNOWLEDGE)
READ OR READ OR DIRECTION OF

WRITE WRITE TRANSFER MAY
CHANGE AT
THIS POINT
NOTES:
1. Combined formats can be used, for example, to control a serial memory. During the first data byte, the internal memory location has to be written. After the start condition is repeated,
data can then be transferred.
2. All decisions on auto-increment or decrement of previously accessed memory locations, etc., are taken by the deSigner of the device.
3. Each byte is followed by an acknowledge as indicated by the A blocks in the sequence.
4. 12C devices have to reset their bus logiC on receipt of a start condition so that they all antiCipate the sending of a slave address.
December 1988 4-5

12 C Bus Specification
ADDRESSING
The first byte after the start condition deter-
mines which slave will be selected by the LSB
I
master. Usually, this first byte follows that o I o OIAxxxxlx x x B
start procedure. The exception is the general
call address which can address all devices. RRSTBYTE SECOND BYTE
When this address is used, all devices (GENERAl. CALL ADDRESS)
should, in theory, respond with an acknowl-
edge, although devices can be made to
ignore this address. The second byte of the Figure 11. General Call Address Format
general call address then defines the action
to be taken.
Definition of Bits in the First H'06'
Byte Is I H'OO' I AI H'02' I AI ABCDOOO I X I A I ABCDOQ1 I X I AI ABCD010 I X I A I p I
The first seven bits of this byte make up the
slave address (Figure 10). The eighth bit Figure 12. Sequence of a Programming Master
(LSB - least significant bit) determines the
direction of the message. A zero on the least
bilities in group 1111 will also only be used for edge this address and behave as a slave
significant position of the first byte means that
extension purposes but are not yet allocated. receiver. The second and following bytes will
the master will write information to a selected
be acknowledged by every slave receiver
slave; a one in this position means that the The combination OOOOXXX has been defined
capable of handling this data. A slave which
master will read information from the slave. as a special group. The following addresses
cannot process one of these bytes must
have been allocated:
ignore it by not acknowledging.
LSB FIRST BYTE The meaning of the general call address is
always specified in the second byte (Figure
-SLAYEADDRESS- Slave
Address R/W 11).
0000 000 a General call address There are two cases to consider:
Figure 10. The First Byte After the
Start Procedure 0000 000 1 Start byte 1. When the least significant bit B is a zero.
2. When the least significant bit B is a one.
When an address is sent, each device in a 0000 001 X CBUS apdress When B is a zero, the second byte has the
system compares the first 7 bits after the start 0000 010 X Address reserved for
following definition:
different bus format
condition with its own address. If there is a
00000110 (H'06') Reset and write the pro-
match, the device will consider itself ad-
0000 all X grammable part of slave
dressed by the master as a slave receiver or
slave transmitter, depending on the R/W bit.
The slave address can be made up of a fixed
and a programmable part. Since it is expected
0000
0000
0000
0000
100
101
110
111
X
X
X
X
}o", "'moO
address by software and
hardware. On receiving this
two-byte sequence, all de-
vices (designed to respond
that identical ICs will be used more than once to the general call address)
in a system, the programmable part of the No device is allowed to acknowledge at the will reset and take in the
slave address enables the maximum possible reception of the start byte. programmable part of their
number of such devices to be connected to The CBUS address has been reserved to address.
the 12 C bus. The number of programmable enable the intermixing of CBUS and 12C Precautions must be taken
address bits of a device depends on the devices in one system. 12C bus devices are to ensure that a device is
number of pins available. For example, if a not allowed to respond at the reception of this not pulling down the SDA
device has 4 fixed and 3 programmable address. or SCL line after applying
address bits, a total of eight identical devices the supply voltage, since
can be connected to the same bus. The address reserved for a different bus these low levels would
format is included to enable the mixing of 12 C block the bus.
The 12C bus committee is available to coordi- and other protocols. Only 12C devices that are
nate allocation of 12C addresses. able to work with such formats and protocols 00000010 (H'02') Write slave address by
are allowed to respond to this address. software only. All devices
The bit combination llllXXX of the slave
which obtain the program-
address is reserved for future extension pur- General Call Address mable part of their address
poses. The general call address should be used to by software (and which
The address 1111111 is reserved as the address every device connected to the 12C have been designed to re-
extension address. This means that the ad- bus. However, if a device does not need any spond to the general call
dressing procedure will be continued in the of the data supplied within the general call address) will enter a mode
next byte(s). Devices that do not use the structure, it can ignore this address by not in which they can be pro-
extended addressing do not react at the acknowledging. " a device does require data grammed. The device will
reception of this byte. The seven other possi- from a general call address, it will acknowl- not reset.
December 1988 4-6

An example of a data transfer of a program-

ming master is shown in Figure t 2 (ABCD
(B)
represents the fixed part of the address).
I
00000100 (H'04') Write slave address by S oooooooo A I MASTER ADDRESS 1 A DATA A I P I
hardware only. All devices
21
which define the program- GENERAL SECOND (n BYTES + ACKNOWLEDGE)
CALL ADDRESS BYTE
mable part of their address
by hardware (and which re-
spond to the general call Figure 13. Data Transfer From Hardware Master Transmitter
address) will latch this pro-
grammable part at the re-
ception of this two-byte se-
quence. The device will not
reset.
S SLAVEADDRHIWMASTER RIW A I DUMPADDRFORHIWMASTER X I A IP I
00000000 (H'OO') This code is not allowed to WRITE
be used as the second
byte. a. Configuring master sends dump address to hardware master
Sequences of programming procedure are
published in the appropriate device data
sheets.
S DUMP ADDR FROM H IW MASTER RIW A P I
The remaining codes have not been fixed and II
WRITE (n BYTES + ACKNOWLEDGE)
devices must ignore these codes.
When B is a one, the two-byte sequence is a b. Hardware master dumps data to selected slave device
hardware general call. This means that the
sequence is transmitted by a hardware mas- Figure 14. Data Transfer of Hardware Master Transmitter Capable of Dumping
ter device, such as a keyboard scanner, Data Directly to Slave Devices
which cannot be programmed to transmit a
desired slave address. Since a hardware
master does not know in advance to which II II
device the message must be transferred, it
can only generate this hardware general call SDA? :
I \.. I (
~UMMY
ACKNOWLEDGE I
I
I
and its own address, thereby identifying itself (HIGH)
to the system (Figure 13). I I I I
--r---f\ f0. r;\ J;\ r,;\ H-
The seven bits remaining in the second byte
contain the device address of the hardware
SCL
I _I \..Jr,\
. \..J - "-t~ , \..J - \..J ACK\..J I _ i
master. This address is recognized by an L~ ~~
intelligent device, such as a microcomputer,
connected to the bus which will then direct !----START BYTE 00000001----1
the information coming from the hardware
master. If the hardware master can also act Figure 15. Start Byte Procedure
as a slave, the slave address is identical to
the master address.
Iy, the more times the microcomputer moni- start byte (00000001) is transmitted. Another
In some systems an alternative could be that tors, or polls, the bus, the less time it can microcomputer can therefore sample the
the hardware master transmitter is brought in spend carrying out its intended function. SDA line on a low sampling rate until one of
the slave receiver mode after the system the seven zeros in the start byte is detected.
Therefore, there is a difference in speed
reset. In this way, a system configuring mas- After detection of this Low level on the SDA
between fast hardware devices and the rela-
ter can tell the hardware master transmitter line, the microcomputer is then able to switch
tively slow microcomputer which relies on
(which is now in slave receiver mode) to to a higher sampling rate in order to find the
software polling.
which address data must be sent (Figure 14). second start condition (Sr) which is then used
After this programming procedure, the hard- In this case, data transfer can be preceded by for synchronization.
ware master remains in the master transmit- a start procedure which is much longer than
A hardware receiver will reset at the reception
ter mode. normal (Figure 15). The start procedure con-
of the second start condition (Sr) and will
sists of:
Start Byte therefore ignore the start byte.
Microcomputers can be connected to the 12 C a) A start condition, (S)
After the start byte, an acknowledge-related
bus in two ways. If an on-chip hardware 12 C b) A start byte 00000001
clock pulse is generated. This is present only
bus interface is present, the microcomputer c) An acknowledge clock pulse
to conform with the byte handling format used
can be programmed to be interrupted only by d) A repeated start condition, (Sr)
on the bus. No device is allowed to acknowl-
requests from the bus. When the device
After the start condition (S) has been trans- edge the start byte.
possesses no such interface, it must con-
mitted by a master requiring bus access, the
stantly monitor the bus via software. Obvious-
December 1988 4-7

r-,
I
SDA "I___________J
SCL
DLEN /
~----------------~
'---_ _ _ _ _ _ _ _-'IL.JL.J L -_ _ _ _ _ _ _ _ _ _ _ _--'I L-J
CO~~I~ON Ag~~:ss ~ I
n DATA BITS
ACK
RELATED
CLOCK PULSE
Figure 16. Data Format of Transmissions With CBUS Receiver/Transmitter
CBUS Compatibility
Existing CBLiS receivers can be connected to V 0D1 _4 =5V:t:10%
the 12 C bus. In this case, a third line called
DLEN has to be connected and the acknowl-
edge bit omitted. Normally, 12 C transmissions
are multiples of 8-bit bytes; however, CBLiS
devices have different formats.
In a mixed bus structure, 12C devices are not
allowed to respond on the CBLiS message. SM--~-t--~~~--~-+----~~----~+
For this reason, a special CBLiS address SCL----~~----~------4_------4_------+_
(0000001 X) has been reserved. No 12 C de-

vice will respond to this address. After the Figure 17. Fixed Input Level Devices Connected to the 12C Bus
transmission of the CBLiS address, the DLEN
line can be made active and transmission,
according to the CBLiS format, can be per- VoD =e.g.3V
formed (Figure 16).
After the stop condition, all devices are again
ready to accept data.
Master transmitters are allowed to generate
SM--~~~--~~----~+-----~+-----~+
CBLiS formats after having sent the CBLiS
SCL----~~----~------~------~------~
address. Such a transmission is terminated
by a stop condition, recognized by all devices.
In the low speed mode, full 8-bit bytes must Figure 18. Devices With a Wide Ra9ge of Supply Voltages Connected
always be transmitted and the timing of the to the I C Bus
DLEN signal adapted.
VIHmin ~ 3V (minimum input High The maximum low-level input current at
If the CBLiS configuration is known and no voltage) VOl max of both the SDA pin and the SCL pin
expansion with CBLiS devices is foreseen, of an 12 C device is -10pA, including the
the user is allowed to adapt the hold time to Devices operating on a fixed supply voltage
leakage current of a possible output stage.
the specific requirements of device(s) used. different from + 5V (e.g. 12L), must also have
these input levels of 1.5V and 3V for Vil and The maximum high-level input current at
VIH, respectively. 0.9VDD of both the SDA pin and SCL pin of an
ELECTRICAL SPECIFICATIONS 12 C device is 10pA, including the leakage
For devices operating over a wide range of
OF INPUTS AND OUTPUTS OF current of a possible output stage.
supply voltages (e.g. CMOS), the following
12C DEVICES levels have been defined: The maximum capacitance of both the SDA
The 12 C bus allows communication between pin and the SCL pin of an 12 C device is 10pF.
Vilmax ~ 0.3VDD (maximum input Low
devices made in different technologies which
voltage) Devices with fixed input levels can each have
might also use different supply voltages. their own power supply of +5V ± 10%. Pull-
VIHmin ~ 0.7VDD (minimum input High
For devices with fixed input levels, operating voltage) up resistors can be connected to any supply
on a supply voltage of + 5V ± 10%, the fol- (see Figure 17).
For both groups of devices, the maximum
lowing levels have been defined:
output Low value has been defined: However, the devices with input levels related
Vilmax ~ 1.5V (maximum input Low to VDD must have one common supply line to
VOl max ~ O.4V (max. output voltage Low)
voltage) which the pull-up resistor is also connected
at 3mA sink current
(see Figure 18).
December 1988 4-8

When devices with fixed input levels are

mixed with devices with VDD-related levels, V DD1 =5V±100f0 V0D2 =5V±10% V OD3 =5V±1O%
the latter devices have to be connected to
one common supply line of + 5V ± 10% along
with the pull-up resistors (Figure 19).
Rp
Input levels are defined in such a way that:
SOA--~-1----+-;-----+-;-----~+---~~r-
1. The noise margin on the Low level is 0.1 SCL.-----4------~-----4 ______~------~
VDD·
2. The noise margin on the High level is 0.2
VDD· Figure 19. Devices With Voo Related LeveJs Mixed With Fixed Input Level
Devices on the I C Bus
3. Series resistors (Rs) up to 300n can be
used for flash-over protection against high
voltage spikes on the SDA and SCL line
(due to flash-over of a TV picture tube, for voo
example) (Figure 20). Vr
~
r
The maximum bus capacitance per wire is
400pF. This includes the capacitance of the
wire itself and the capacitance of the pins
l I'C
OEVICE JI O:'CE I
connected to it.
Rs Rs Rs Rs Rp Rp
TIMING SOA
The clock on the 12C bus has a minimum Low SCL
period of 4.711S and a minimum High period of LD05650S
411S. Masters in this mode can generate a bus Figure 20. Serial Resistors (Rs) for Protection Against High Voltage
clock with a frequency from 0 to 100kHz.
All devices connected to the bus must be LOW-SPEED MODE Data Format and Timing
able to follow transfers with frequencies up to As explained previously, there is a difference The bus clock in this mode has a Low period
100kHz, either by being able to transmit or in speed on the 12 C bus between fast hard- of 130l1s ± 2511S and a High period of
receive at that speed or by applying the clock ware devices and the relatively slow micro- 390l1s ± 2511S, resulting in a clock frequency
synchronization procedure which will force computer which relies on software polling. of approx. 2kHz. The duty cycle of the clock
the master into a wait state and stretch the For this reason a low speed mode is available has this Low-to-High ratio to allow for more
Low periods. In the latter case the frequency on the 12C bus to allow these microcomputers efficient use of microcomputers without an
is reduced. to poll the bus less often. on-chip hardware 12C bus interface. In this
mode also, data transfer with acknowledge is
Figure 21 shows the timing requirements in Start and Stop Conditions obligatory. The maximum number of bytes
detail. A description of the abbreviations used In the low-speed mode, data transfer is pre-
is shown in Table 2. All timing references are transferred is not limited (Figure 22).
ceded by the start procedure.
at V1Lmax and VILmln.
SDA
SCL
Figure 21. Timing Requirements for the 12 C Bus
December 1988 4-9

Table 2. Timing Requirement for the 12 C Bus
LIMITS
Min Max
fscL SCL clock frequency 0 100 kHz
tsuF Time the bus must be free before a new transmission can start 4.7 I1s
tHO; STA Hold time start condition. After this period the first clock pulse is generated 4 I1s
tLOW The Low period of the clock 4.7 I1s
tHIGH The High period of the clock 4 I1s
tsu; STA Setup time for start condition (Only relevant for a repeated start condition) 4.7 I1s
tHO; OAT Hold time DATA
for CBUS compatible masters 5 I1s
for 12 C devices O· I1S
tsu; OAT Setup time DATA 250 ns
tR Rise time of both SDA and SCL lines 1 I1s

tF Fall time of both SDA and SCL lines 300 ns
tsu; STO Setup time for stop condition 4.7 I1S

NOTES:
All values referenced to VIH and VIL levels.
* Note that a transmitter must internally provide, a hold time to bridge the undefined region (300ns max.) of the falling edge of SCL.
C~~
~...,
SDA "1\:
I \jol----~(.(_J
I
I I I I I I
SCL~~~-~
I s I I I I I Sr p
1....---' ! IL---..J L.....J I IL---JI IL---J L-......J
CO~~ON START BYTE ACK~~~~~DGE R~e::rED ADDRESS ACK DATA n BYTES ACK I CO~:'DN
(HIGH) CONDITIDN
Figure 22. Data Transfer Low-Speed Mode
SDA
SCL
l----tHIGH----~1
Figure 23. Timing Low-Speed Mode
December 1988 4-10

LOW SPEED MODE In this mode, a transfer cannot be terminated

during the transmission of a byte.
CLOCK tLOW - t 30l'S ± 251's
DUTY CYCLE tHIGH - 390l's ± 251's The bus is considered busy after the first start
1:3 Low-to-High (Duty cycle of condition. It is considered free again one
clock generator) minimum clock Low period, 1051's, after the
START BYTE 0000 0001 detection of the stop condition. Figure 23
MAX. NO. OF BYTES UNRESTRICTED shows the timing requirements in detail, Table
PREMATURE TERMINATION OF TRANSFER NOT ALLOWED 3 explains the abbreviations.
ACKNOWLEDGE CLOCK BIT ALWAYS PROVIDED
ACKNOWLEDGEMENT OF SLAVES OBLIGATORY
Table 3. Timing Low Speed Mode
LIMITS
Min Max
tBUF Time the bus must be free before a new transmission can start 105 I's
tHO; STA Hold time start condition. After this period the first clock pulse is generated 365 p.s
tHO; STA Hold time (repeated start condition only) 210 p.s
tLOW The Low period of the clock 105 155 I'S

tHIGH The High period of the clock 365 415 I'S
tsu; STA Setup time for start condition (Only relevant for a repeated start condition) 105 155 p.s
tHO; tOAT Hold time DATA

for CBUS compatible masters 5 I'S
for 12 C devices O' p.s
tsu; OAT Setup time DATA 250 ns

tR Rise time of both SDA and SCL lines 1 I'S
tF Fall time of both SDA and SCL lines 300 ns
tsu; STO Setup time for stop condition 105 155 p.s
NOTES:
All values referenced to V 1H and V 1L levels .
• Note that a transmitter must internally provide a hold time to bridge the undefined region (300ns max.) of the falling edge of seL.
December 1988 4-11

APPENDIX A In Graph 2, RSmax against Rp is shown. In Graph 3, the bus capacitance - RPmax
Maximum and minimum values of the pull-up 2) The bus capacitance is the total ca- relationship is shown.
resistors Rp and series resistors Rs (See pacitance of wire, connections, and 3) The maximum high-level input current
Figure 20). pins. This capacitance limits the maxi- of each input! output connection has a
mum value of Rp because of the specified value of 10j.iA max. Due to
In a 12C bus system these values depend on specified rise time of 1MS. the desired noise margin of 0.2 VDD
the following parameters: for the high level, this input current
- Supply voltage limits the maximum value of Rp. This
- Bus capacitance limit is dependent on VDD.
- Number of devices (input current + leak-
age current) In Graph 4 the total high-level input cur-
1) The supply voltage limits the min- rent - RPmax relationship is shown.
imum value of the Rp resistor due
to the specified 3mA as minimum 20
sink current of the output stages,
at O.4V as maximum low voltage. 18
In Graph 1, VDD against Rpmin is Si
shown.
<;.
0:
w 12
__-L____L-__- L__
3
~
O~ ~
o 400 800 1200 1600 ::Ii

:::>
MAXIMUM VAWE Rs (2) :I!
~
:I!
Graph 2
oL-__ __-L__
~ ~ ____ L-~
,
o 40 80 120 180 200
TOTAL HIGH LEVEL INPUT CURRENT (jA)
,
20
18 Graph 4
lii"
O~
o
__-L____L-__-L__
12
~
16
os.
.t
w
3
12
\\ 12C LICENSE
Purchase of Signetics or Philips 12C compo-
~ /Rs=O
::Ii nents conveys a license under the Philips 12C
:::>
patent rights to use these components in an
MAX.R~~
::Ii
Graph 1
~ ~
12C system, provided that the system con-
The desired noise margin of 0.1 VDD for the

@VOO=j .......:::::
-=
forms to the 12 C standard specification as
defined by Philips.
low level limits the maximum value of Rs. o
o 100 200 300 400
BUS CAPACITANCE (PF)
Graph 3
December 1988 4-12

Signetics 12C PERIPHERAL
SELECTION GUIDE
General Purpose ICs Application-Oriented ICs 68000-Based CMOS IlProcessor
SCC68070: 68000 CPU/MMU/UARTI
LCD Drivers Video/Radio/Audio DMNtimer
PCF8566: 96-segment LCD driver PCF8200: Voice synthesizer (malel
1:1 -1:4 Mux female speech)
SAA3028: Transcoder (RC-5) for IR
. 80C51-Based CMOS IlControllers·
PCF8576: 160-segment LCD driver
remote control S80C552: ROM-less version of
1:1 -1:4Mux
Digital tuning circuits for S83C552
PCF8517/A: 64-segment LCD driver SAB3035/36/37:
computer-controlled TV S80C652: ROM-less version of
1:1 -1:2Mux
TDA8440: Video/audio switch S83C652
PCF8578i79: Row/column LCD dot-
YUV/RGB matrix switch S83C552: 256-byte RAMISk RaMI
matrix driver; 1 :S - 1 :32 Mux TDA8443/A:
TEA6000/61 00: FMlIF and digital tuning IC ADC/UART
for computer-controlled S83C652: 256-byte RAMISkI ROM
I/O Expandors radio S83C751 : 64-byte RAM/2k ROM
PCF85741A: S-bit remote I/O port WC S87C552: EPROM version of
TEA6300: Sound fader control and
bus to parallel converter) SS3C552·
.". preamplifier/source
I PCF8584: S-bit parallel to 12 C S87C652: EPROM version of
-'> selector for car radio
c.u converter· Sound fader control with S83C652*
TEA6310T:
SAA1064: 4-digit LED driver tone and volume control for S87C751: EPROM version of
SAA1300: 5-bit high-current driver car radio S83C751
TSA5510: PLL frequency synthesizer +al50 available with extended lemperature ranges
Data Converters for radio
PCF8591: 4-channel, S-bit Mux TSA6057: PLL frequency synthesizer 8048 Instruction-Set Based CMOS
ADC + one DAC for radio IlControllers
TDA8442: Quad 6-bit DAC
Telecom PCF84COO: 256-byte RAM/bond-out
TDA8444: Octal 6-bit DAC version for prototype
NE5750/51: Audio processor pair'"
PCD3311/12: Tone generator (DTMF/ development
Memory modem/musical) PCF84C21: 64-byte RAM/2k ROM
PCF8570/C: 256-byte static RAM PCD3341: Advanced 10 to 11 O-number PCF84C41 : 128-byte RAMl4k ROM
PCF8571: 12S-byte static RAM repertory dialer with LCD PCF84C81: 256-byte RAMISk ROM
PCF8581: 12S-byte EEPROM· control PCF84C85: 256-byte RAMISk ROM/
PCF8582A: 256-byte EEPROM PCD3343: Microcontroller with 224- Extended 1/0
PCF8583: 256-byte RAM/clockl byte RAMl3k ROM PCF84C430: 12S-byte RAMl4k RaMI
calendar PCD3348: Microcontrolier with 256- 96-segment LCD driver·
byte RAMISk ROM
Clock/Calendars UMA1000T: Data processor for mobile
PCF8573: Clocklcalendar telephones·
Clocklcalendar/256-byte UMA1010T: 1GHz frequency
PCF8583:
RAM synthesizer for mobile • Future Device
telephones·
Signetics Section 5
Development Support
Tools
INDEX
Development Support Tools .................................. 5-1
In-Circu~ Emulator for 8051 or 8052 Microcontroller ............... 5-2
In-Circuit Emulator for 80C451 Microcontroller. . . . . . . . . . . . . . . . . . .. 5-4
In-Circuit Emulator for 83C451 Microcontroller. . . . . . . . . . . . . . . . . . .. 5-6
In-Circu~ Emulator for 80C552 Microcontroller . . . . . . . . . . . . . . . . . . .. 5-8
In-Circuit Emulatorfor 80C652 Microcontroller ................... 5-10
In-Circuit Emulatorfor 83C751 Microcontroller. . . . . . . . . . . . . . . . . .. 5-12
ASM51 8051 Macro Cross Assembler ......................... 5-14
SPGM-100 EPROM Microcontroller and Standard EPROM
Programmer ............................................. 5-16
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lator hardware, host emulation software, cross-assembler,
DEVELOPMENT SUPPORT TOOLS user's manuals, cables, and power supply. Note that these
Signetics stocks development support tools to help simplify emulators do not include provisions for programming
your design activities. These include: ('burning') the EPROM in EPROM-based micro-
controllers.
c In-circuit emulation development systems
c Cross-assemblers CROSS-ASSEMBLER
C Low-cost EPROM programming equipment The cross-assembler provided with the development system
package is also available separately. This assembler sup-
In addition, Signetics works closely with many 'third-party' ports macros and conditional assembly operations and is
vendors who provide support tools for our wide variety of designed to run on an IBM-PC or compatible processor.
80C51-based microcontroller derivatives. This assembler uses an external text file to define the
architecture of specific microcontrollers. Support for new
DEVELOPMENT SYSTEMS microcontroller types can be added by creating a simple
In most cases, our development systems are available in text file to define the new micro-controller, thereby allow-
two versions for ROM and ROMless applications. The ing the assembler to support a variety of prodact deriva-
ROM emulation products are capable of supporting all tives now and in future applications.
versions of a given device type including EPROM, ROM,
and ROMless devices. For example, the SMI-83C451 em- EPROM PROGRAMMING SUPPORT
ulator can support designs based on either the 87C451, Signetics works closely with. major suppliers of EPROM
83C451, or 8OC451. In contrast, a ROMless emulator can programming equipment to support our family of EPROM
only support applications designed for a ROMless micro- micro-controllers. As a result, EPROM programming sup-
controller. For example, the SMI-80C451 emulator can port is available within the programming facilities of many
only support applications using the 8OC451. major distributors and customers.
These development systems are designed to connect to the Your local Signetics sales office or representative can
serial port of an IBM-PC or compatible personal com- provide a list of manufacturers of EPROM programming
puter. The development system package includes the emu- equipment that offer programming support products for
Signetics EPROM microcontrollers.
SIGNETICS MICROCONTROLLER DEVELOPMENT SYSTEMS
The emulator package includes emulator hardware, power supplies, Interface cables, host software and cross-assembler.
This package requires the use of an IBM-PC or 100% compatibles with 640k RAM, PC DOS version 2.0 or later and an
RS232 port.
EPROM MICROCONTROLLER PROGRAMMING SYSTEM
Mltl~@J.i~§t#n tki&YMlt@rWWm%ltW#jjtMird;a;dm!~ltltml_m"~~$.tl@mN H!@tr . .·. . . . . . . . I.)n'td

Adapter Sockets for SPGM-100SD
Part No. Microcontroller DIP LCC
SAM 751SD 87C751 24-Pin
SAM 751ASD 87C751 28-Pin
SAM 51SD 87C51 40-Pin
SAM-451SD 87C451 64-Pin
SAM-752SD 87C752 28-Pin
SHIPMENTS THROUGH SIGNETICS DISTRIBUTORS ONLY
February 1989 5-1

System Overview
Signetics-8052
In-Cirquit Emulator
for 8051 or 8052
Microcontroller
• Serially linked to IBM PC or 100% • Over 128,000 Break Triggers and 64,000
compatible hosts Trace Triggers
• Advanced menu driven human interface • Emulation Memory:
• Real time and transparent emulation up to Standard Optional
~ Program 16K 64K
16 MHz
~ External Data 16K 64K
• Disassembler and Single Line Assembler
• Full Symbolic Debug Capability
• Examine/Modify Memory capabilities
• High Level Language Support
• 16 Break and Trace Trigger Conditions
• Up to 64K Pass Counts
• Supports both modes:
Microcontroller • Separate Program and Data Memory Mapping
Microprocessor in 16 byte blocks
• Experiment Editor/Compiler
• 9 Probe Clips
7 External Events • Trace with 2K frames
1 External Trigger Input • Opcode Class Editor
1 External Trigger Output
PHILIPS 98-8270-010
5-2 1029-OOO/688IIM
Functional Description Support
The Signetics-8052 is an in-circuit emulator which is designed for use in The Signetics-8052 emulator not only assists the designer in developing, testing
developing, testing and debugging designs based on 8051 or 8052 single and debugging 8051 or 8052 microcontroller designs, but is also backed by
chip microcontrollers. The Signetics-8052 allows the development of Signetics with an extensive service and support policy that includes:
hardware and software designs to occur simultaneously. • Updates to the Signetics User's Manual and Signetics host Operating System
The Signetics-8052 emulator assists in the following design phases: software that are provided at no charge for a ninety (90) day period.
• Software Development • Toll free phone number (l-800-A-HLP-4-51) to resolve system hardware
• Manufacturing and/or software concerns.
• Integration of target software and system hardware • A 72-hour repair on disabled systems under warranty.
• Field Service
Features Description
Emulator Functions Experiment High Level Language
• Microcontrollers supported: • Used to specify complex break and trace • 'C' and PLM support
S031 SOC31 S032 triggers • Variables and Line number break/trace triggers
SOSI SOCSI S052 • Uses the if-then construct • Variables Accessible
S7C51 • Allowable trigger conditions are: • Step - Proceed and Step - Trace of Line
• Perfonnance PC address numbers
Real-time 3.5 to 16 MHz PC address range
• Transparency: Opcode value
Operational and electrical apcode class
SymbOlic Debug
• Examine and modify: Special function registers
Program Direct byte address • User and Pre-Defined Symbols
Internal data Direct byte address range • Supports MetaLink., Enertec, lAR, Archimedes,
External data Direct bit address Signetics, Microtec Research or Intel aMF files
Direct bit address range • Use a name not address to alter content of:
Immediate operand value bits, bytes, code
User Interface Read/write to bit or direct addresses
External data address
• Advanced menu driven operating system External data address range Electrical Specification
• 11 functional capabilities: Logical AND or OR of any of the above
Load OS-Escape Pass count overflow Input Power (typical):
Upload Help External input 1.5 amps @ + 5 volts DC +/ - 5%
Download Configure • Over; 12S,OOO break triggers
Store Restore 64,000 trace triggers
Interrogate Exit • Experiment Editor allows user to create or Mechanical Specification
Macro modify experiments by:
Emulator dimensions:
Edit Delete 1.0" x 7.0" x 5.5"
Compile Store 2.5cm x 17.Scm x 14.0cm
Mode Load Specify Opcode Class
Target system cable length:
• apcode class is collection of various 8051 14.0"
• Allows user to emulate all the operating modes instructions that make up a set.
of; 35.6cm
Set is user defined Emulator and target system cable weight:
Full operation with external address/data bus Opcode class editor allows user to create,
Single-chip operation with NO external 2.01bs.
delete or edit ape ode classes
address/data bus 0.9 kg
Emulator probe head:
Compatible with 600 mil wide 40 pin DIP on
Examine/Modify Memory 100 mil centers
Interrogation
• Program memory operations:
• Allows the user to: Disassemble
Run experiments Single line assemble Host Specification
Examine the system status Examine/modify raw data
Set break and trace triggers An IBM PC, PC XT, PC AT or 100%
Mapping
Examine/modify data compatible system with 640K bytes of RAM.
• Microcontroller internal and external data PC-DOS 2.0 or later.
• 16 functional capabilities: memory operations:
Run Two (2) floppy disk drives.
Dump One (I) RS232C interface card for the PC and
Single-step Scan and modify
Reset cable.
Fill
OS-Escape Move
Set pass count Search
Set simple break and trace triggers warranty
Compare
Set repetition counter Mapping
Set phantom break and trace triggers Ninety (90) days limited warranty, parts and
Examine/modify addressable bits labor.
Set trace triggers (start, end & center)
Tum trace trigger ON/OFF
View up to 2K of trace buffer
Examine/modify:
Internal data memory
External data memory
Program memory
Macro
• Repetitive routine
• User created, edited and
callable at any time
Signetics
a division 01 North American Philips Corporation
Emulator experiments
MetaLink is a Irademark of MetaLink. Corporation. Signellcs Company
pc-OOS, PC. PC XT and PC AT are trademarks of IBM. 811 E. Arques Avenue
IBM is a registered trademark of IBM Corporation. P.O. Box 3409
Intel is a registered trademark of Intel Corporation.
©METALINK CORPORATION 1988
Sunnyvale, California 94088-3409
Telephone 408/991-2000
System Overview
Signetics-80C451
In-Circuit Emulator for
80C451 Microcontroller
• Serially linked to IBM PC or 100% • Opcode Class Editor

compatible hosts • Over 128,000 Break and Trace Triggers
• Real time and transparent emulation up to - 64K Program
12 MHz - 64K External Data
• Disassembler and Single Line Assembler • Full Symbolic Debug Capability
• Examine/Modify Memory capabilities • Up to 64K Pass Counts
• 16 Break and Trace Trigger Conditions • Separate Program and Data Memory Mapping
• Supports 80C451 in 16 byte blocks
• 9 Probe Clips • Experiment Editor/Compiler
1 External Trigger Input
e PHILIPS
PHILIPS
98-8270-070
1034-0001988/IM
The Signetics-80C451 is an in-circuit emulator which is designed for The Signetics-80C451 emulator not only assists the designer in devel-
use in developing, testing and debugging designs based on an 80C451 oping, testing and debugging 80C451 microcontroller designs, but is
single chip microcontroller. The Signetics-80C451 allows the devel- also backed by Signetics with an extensive service and support policy
opment of hardware and software designs to occur simultaneously. that includes:
The Signetics-80C451 emulator assists in the following design phases: • Updates to the Signetics User's Manual and Signetics host Oper-
• Software Development _ Integration of target software and ating System software that are provided at no charge for a ninety
• Manufacturing system hardware (90) day period .
• Field Service • Toll free phone number (l-800-A-HLP-4-51) to resolve system
hardware and software concerns.
• A 72-hour repair on disabled systems under warranty.
Emulator Functions Experiment Macro
• Microcontrollers supported: • Used to specify break and trace triggers • Repetitive routine
80C45 I • Uses the if-then construct • User created, edited and callable at any time
• Performance • Allowable trigger conditions are:
Real-time .5 MHz to 12 MHz PC address Symbolic Debug
• Transparency: PC address range
• User and Pre-Defined Symbols
Operational and electrical Ope ode value
• Supports MetaLink, Enertec, I AR, Archimedes,
• Examine and modify: Ope ode class Signetics, Microtec Research or Intel OMF files
Program Special function registers
• Use a name not address to alter content of:
Internal data Direct byte address bits, bytes, code
External data Direct byte address range
Direct bit address Optional Products
User Interface Direct bit address range
Immediate operand value • MetaWARE Converter compatible with 900
TN
• Advanced menu driven operating system mil wide 64 pin DIP on 100 mil centers.
• 11 functional capabilities: Read/write to bit or direct addresses
Load OS-Escape External data address
External data address range Electrical Specification
Upload Help
Download Configure Logical AND or OR of any of the above Input Power (typical):
Store Restore Pass count overflow 1 amp @ +25 volts DC +/ -5%
Interrogate Exit External input
Macro • Over 128,000 break and trace triggers Mechanical Specification
• Experiment Editor allows user to create or Emulator dimensions:
Interrogation modify experiments by: 2.0" X 11.0" X 7.62"
Edit Delete 5.1 em X 27.9 cm X 19.3 em
• Allows the user to: Compile Store
Run experiments Target system cable length:
Load Specify Opcode Class 14.0"
Examine the system status • Opcode class is collection of 80C45 1
Set break and trace triggers 35.6 em
instructions that make up a set. Emulator and target system cable weight:
Examine/modify data Set is user defined
• 15 functional capabilities: 5.01bs.
Opcade class editor allows user to create, 2.2 kg
Run delete or edit Opcode classes
Single-step Emulator probe head:
Reset Compatible with 68 lead PLCC (J-Bend) on
Examine/Modify Memory 50 mil centers
OS-Escape
Set pass count • Program memory operations:
Set simple break and trace triggers Disassemble Host Specification
Set repetition counter Single line assemble An [BM PC, PC XT, PC AT or 100%
Set phantom break and trace triggers Examine/modify raw data compatible system with 640K bytes of RAM.
Set trace triggers (start, end & center) Mapping PC-DOS 2.0 or later.
View up to 4K of trace buffer • Microcontroller internal and external data Two (2) floppy disk drives.
Examine/modify: memory operations: One (I) RS232C interface card for the PC and
Special Function Registers Dump cable
Internal data memory Scan and modify
External data memory Fill Warranty
Program memory Move
Search Ninety (90) days limited warranty, parts and
Emulator experiments labor.
Compare
Mapping
Examine/modify addressable bits
Ordering Information Signefics

Order Code: SMI-80C451SD
Signetics Company
MelaLink is a trademark of MetaLink Corporation. 811 E. Arques Avenue
PC-DOS, PC, PC XT and PC AT are trademarks of IBM P.O. Box 3409
IBM is a registered trademark of IBM Corporation.
Intel is a registered trademark of Intel Corporation. Sunnyvale, California 94088-3409
©METALINK CORPORATION 1988 5--5 Telephone 408/991-2000
System Overview
Signetics-83C451

• Disassembler and Single Line Assembler • Full symbolic Debug Capability
in 16 byte blocks
• Supports both modes:
80C45l with External Addresses • Experiment Editor/Compiler
83C45l Single Chip • Trace with 4K frames
• 9 Probe Clips
7 External Events
PHILIPS 98-8270-030
5--6 1027-OOO/6SSIIM
The Signetics-83C451 is an in-circuit emulator which is designed for The Signetics-83C45I emulator not only assists the designer in developing, testing
use in developing, testing and debugging designs based on an 83C451 and debugging 83C45 I microcontroller designs. but is also backed by Signetics
single chip microcontroller. The Signetics-83C45I allows the with an extensive service and support policy that includes:
development of hardware and software designs to occur simultaneously. • Updates to the Signetics User's Manual and Signetics host Operating System
The Signetics-83C451 emulator assists in the following design phases: software that are provided at no charge for a ninety (90) day period.
• Software Development • Toll free phone number (l-800-A-HLP-4-51) to resolve system hardware and
• Manufacturing software concerns.
• Field Service
Emulator Functions Experiment Symbolic Debug
• Microcontrollers supported; • Used to specify break and trace triggers • User and Pre-Defined Symbols
83C45 1 80C45 1 87C45 1 • Uses the if-then construct • Supports MetaLink, Enertec, JAR, Signetics,
• Perfonnance • Allowable trigger conditions are: Archimedes, Microtec Research or Intel OMF
Real-time .5 MHz to 12 MHz PC address files
• Transparency; PC address range • Use a name not address to alter content of:
Operational and electrical Opcode value bits, bytes, code
• Examine and modify: Opcode class
Internal data Direct byte address Optional Products
Direct bit address • Converter compatible with 900 mil wide 64 pin
Direct bit address range DIP on 100 mil centers.
User Interface Immediate operand value
Read/write to bit or direct addresses
• Advanced menu driven operating system External data address Electrical Specification
• 11 functional capabilities: External data address range
Load OS-Escape Input Power (typical):
Logical AND or OR of any of the above
Upload Help 1 amp @ + 23 volts DC +/- 5%
Pass count overflow
Download Configure External input
Store Restore • Over 128,000 break and trace triggers
Macro modify experiments by: Emulator dimensions:
Edit Delete 2.0" x 11.0"x 7.62"
Compile Store 5.1cm x 27,9cm x 19.3cm
Mode Load Specify Opcode Class Target system cable length:
• Opcode class is collection of 83C45 I 14.0"
• Allows user to emulate all the operating modes instructions that make up a set.
of the 83C45 1: 35.6cm
Full 8OC451 operation with external address bus
Opcode class editor allows user to create, 5.0Ibs.
Single-chip 83C451 with NO external address
delete or edit Opcode classes 2.2 kg
bus and 4K of on-chip code memory
Emulator probe head:
Compatible with 68 lead plastic leaded chip
Examine/Modify Memory carrier (J-bend) on 50 mil centers
Interrogation
• Allows the user to: Disassemble
Run experiments Host Specification
Single line assemble
Examine the system status
Examine/modify raw data An IBM PC, PC XT, PC AT or 100%
Set break and trace triggers
Mapping compatible system with 640K bytes of RAM.
Examine/modify data
• Microcontroller internal and external data PC-DOS 2.0 or later.
• 15 functional capabilities: memory operations:
Run Two (2) floppy disk drives.
Dump One (I) RS232C interface card for the PC
Single-step
Scan and modify and cable.
Reset Fill
OS-Escape
Move
Set pass count
Search
Set simple break and trace triggers
Compare Warranty
Set repetition counter
Mapping Ninety (90) days limited warranty, parts and
Set phantom break and trace triggers
Set trace triggers (start, end & center)
View up to 4K of trace buffer
Examine/modify:
Special Function Registers Macro
Internal data memory
Signetics
External data memory • User created, edited and callable
Program memory at any time

Signetics Company
MetaLink is a trademark of MetaLink Corporation 811 E. Arques Avenue
pc-OOS. pc. PC XT and PC AT are trademarks of IBM. P.O. Box 3409
Intel is a registered trademark of Intel Corporation Sunnyvale, California 94088-3409
©METALlNK CORPORATION 1988 5--7 Telephone 408/991-2000
System Overview
Signetics-80C552

I External Trigger Input
PHILIPS
98-8270-060
5--8 103Q{lOO!688IIM
The Signetics-80C552 is an in-circuit emulator which is designed for The Signetics-80CSS2 emulator not only assists the designer in developing, testing
use in developing, testing and debugging designs based on an 80C552 and debugging 80C552 microcontroller designs, but is also backed by Signetics
single chip microcontroller. The Signetics-80C552 allows the with an extensive service and support policy that includes:
The Signetics-80C552 emulator assists in the following design phases: software that arc provided at no charge fur a ninety (90) day period.
• Software Development • Toll free phone number (l-800-A-HLP-4-51) to resolve :'!ystem hardware and
• Integration of target software and system hardware • A 72-hour repair on disabled systemr, under warranty.
• Field Service
Emulator Functions Experiment Symbolic Debug
• Microcontrollers supported: • Used to specify break and trace triggers • User and Pre-Defined Symbols
8OC552 • Uses the if-then construct • Supports MetaLink, Enertec, IAR, Signetics,
• Perfonnance • Allowable trigger conditions are: Archimedes, Microtec Research or Intel OMF
Real-time 3.5 MHz to 12 MHz PC address files
• Transparency: PC address range • Use a name not address to alter content of:
Operational and electrical Opcode value bits, bytes, code
• Examine and modify: Opcode class
Internal data Direct byte address Optional Products
Direct bit address • Converter
Direct bit address range
Read/write to bit or direct addresses Electrical Specification
• Advanced menu driven operating system External data address
• 11 functional capabilities: External data address range Input Power (typical);
Load OS-Escape Logical AND or OR of any of the above I amp @ + 23 volts DC +/- 5%
Upload Help Pass count overflow
Store Restore • Over 128,000 break and trace triggers Mechanical Specification
Interrogate Exit • Experiment Editor allows user to create or
Macro Emulator dimensions:
modify experiments by: 2.0" x 11.0" x 7.62"
Edit Delete 5.lcm x 27.9cm x 19.3cm
Compile Store Target system cable length:
Interrogation Load Specify Opcode CIass 14.0"
• Opcode class is collection of 80C552 35.6cm
• Allows the user to: instructions that make up a set.
Run experiments Emulator and target system cable weight:
Set is user defined 5.0Ibs.
Opcode class editor allows user to create, 2.2 kg
delete or edit Opcode classes Emulator probe head:
Examine/modify data
• 16 functional capabilities: Compatible with 68 lead plastic leaded chip
Run carrier (J-bend) on 50 mil centers
Single-step Examine/Modify Memory
Reset • Program memory operations:
OS-Escape Disassemble Host Specification
Set pass count Single line assemble
Set simple break and trace triggers An IBM PC, PC XT, PC AT or 100%
Examine/modify raw data compatible system with 640K bytes of RAM.
Set repetition counter Mapping
Set phantom break and trace triggers PC-DOS 2.0 or later.
• Microcontroller internal and external data Two (2) floppy disk drives.
Set trace triggers (start, end & center) memory operations:
View up to 4K of trace buffer One (I) RS232C interface card for the PC
Dump and cable.
Examine ND data Scan and modify
Examine/modify: Fill
Special Function Registers Move
Internal data memory Search warranty
External data memory Compare Ninety (90) days limited warranty, parts and
Program memory Mapping labor.
Emulator experiments Examine/modify addressable bits
Macro
• User created, edited and
callable at any time
Signefics
a division of North Americon Philips Corporotion
Signetics Company
MetaLink is a trademark of MetaLink Corporation.
PC-OOS, PC, PC XT and PC AT are trademarks of IBM, 811 E. Arques Avenue
IBM is a registered trademark of IBM Corporation. P.O. Box 3409
cMETALINK CORPORATION 1988 5-9 Telephone 408/991-2000
System Overview
Signetics-80C652


PHILIPS 98-8270-020
5-10 1031-o00I688/IM
The Signetics-80C652 is an in-circuit emulator which is designed for The Signetics-80C652 emulator not only assists the designer in developing, testing
use in developing. testirig and debugging designs based on an 8OC652 and debugging 80C652 microcontroller designs, but is also backed by Signetics
single chip microcontroller. The Signetlcs-80C652 allows the with an ex.tensive service and support policy that includes:
The Signetics-8OC652 emulator assists in the following design phases: software that are provided at no charge for a ninety (90) day period.
• Software Development • Toll free phone number (1-8oo-A-HLP-4-51) to resolve system hardware and
• Manufacturing software concerns,
• Field Service
80C652 • Uses the if-then construct • User created, edited and callable at any time
• Perfonnance • Allowable trigger conditions are:
Real-time 3.5 MHz to 12 MHz PC address
• Transparency: PC address range Symbolic Debug
Operational and electrical Opcode value
• Examine and modify: Opcode class • User and Pre-Defined Symbols
Program Special function registers • SuPPOrts MeiaLink, Enertec, JAR, Signetics,
Internal data Direct byte address Archimedes, Microtec Research or Intel OMF
External data Direct byte address range files
Direct bit address • Use a name not address to alter content of:
Direct bit address range bits, bytes, code
Read/write to ·bit or direct addresses
• Advanced menu driven operating system External data address Electrical Specification
• II functional capabilities: Externlll data address range
Load OS-Escape Input Power (typical):
Logical AND or OR of 'my of the above
Upload Help I amp@ + 23 volts DC +/- 5%
Pass coUnt overflow
Store Restore • Over 128,000 break and trace triggers
Macro modify experiments by: Emulator dimensions:
Edit Delete 2.0" X 11.0" X 7.62"
Compile Store S.lcm x 27.9cm x 19.3cm
Interrogation Load Specify Opcode Class Target system cable length:
• Opcode class is collection of SOC6S2 14.0"
• Allows the user to: instructions that make up a set.
Run experiments 35.6cm
Examine the system status Opcode class editor allows user to create,
Set break and trace triggers 5.0lbs.
delete or edit Opcode classes 2.2 kg
Examine/modify data
• 15 functional capabilities: Emulator probe head:
Run Compatible with 40 lead DIP on 100 mil
Single-step Examine/Modify Memory centers
Reset • Program memory operations:
OS-Escape Disassemble
Set pass count Single line assemble Host Specification
Set simple break and trace triggers Examine/modify raw data An IBM pc, PC XT, pc AT or 100%
Set repetition counter Mapping compatible system with 640K bytes of RAM.
Set phantom break and trace triggers • Microcontroller internal and external data PC-DOS 2.0 or later.
Set trace triggers (start, end & center) memory operations: Two (2) floppy disk drives.
View up to 4K of trace buffer Dump One (1) RS232C interface card for the PC
Examine/modify: Scan and modify and cable.
Special Function Registers Fill
Internal data memory Move
External data memory Search
Program memory Compare Warranty
Emulator experiments Mapping Ninety (90) days limited warranty, parts and
Signetics
Signeties Company
MetaLink is a trademark of MetaLink Corporation. 811 E. Arques Avenue
PC-DOS, PC, PC XT and pC AT are trademarks of IBM.
mM is a registered trademark of IBM Corporation.
P.O. Box 3409
oMETALINK CORPORATION 1988 5-11 Telephone 408/991-2000
System Overview
Signetics-83C751
• Serially linked toIBM PC or 100% • Opcode Class Editor

compatible hosts • Break and Trace Triggers
16 MHz • Fuil symbolic Debug Capability
• Disassembler and Single Line Assembler • Up to 64K Pass Counts
• Examine/Modify Memory capabilities • Program Mapping in 16 byte blocks
• 14 Break and Trace Trigger Conditions • Experiment Editor/Compiler
• Supports 83C751 • Trace with 4K 4ames
• 9 Probe Clips
7 External Events
PHILIPS98-8270-040
5-12 1028-000J688/1M
The Signetics-83C751 is an in-circuit emulator which is designed for The Signetics-83C751 emulator not only assists the designer in developing, testing
use in developing, testing and debugging designs based on an 83C751 and debugging 83C751 microcontroller designs, but is also backed by Signetics
single chip microcontroller. The Signetics-83C75I allows the with an extensive service and support policy that includes:
The Signetics-83C75I emulator assists in the following design phases: software that are provided at no charge for a ninety (90) day period.
• Software Development • Toll free phone number (l-800-A-HLP-4-51) to resolve system hardware and
• Field Service
83C751, 87C751 • Uses the if-then construct • User created, edited and callable at any time
• Performance • Allowable trigger conditions are:
Real-time 3.5 MHz to 16 MHz PC address
• Transparency: PC address range Symbolic Debug
Operational and electrical Opcode value
• Examine and modify: Opcode class • User and Pre-Defined Symbols
Program Special function registers • Supports MetaLink, Enertec, IAR, Signetics,
Internal data Direct byte address Archimedes, Microtec Research or Intel OMF
Direct byte address range files
Direct bit address • Use a name not address to alter content of:
Direct bit address range bits, bytes, code
User Interface
Immediate operand value
• Advanced menu driven operating system Read/write to bit or direct addresses
• 11 functional capabilities: Logical AND or OR of any of the above Electrical Specification
Load OS-Escape Pass count overflow
Upload Help Input Power (typical):
External input
Download Configure I amp @ + 23 volts DC +/- 5%
• Break and trace triggers
Store Restore • Experiment Editor allows user to create or
Interrogate Exit modify experiments by:
Macro Edit Delete Mechanical Specification
Compile Store Emulator dimensions:
Load Specify Ope ode Class 2.0" x 11.0" x 7.62"
Interrogation • Opcode class is collection of 83C751 5.lcm x 27.9cm x 19.3cm
instructions that make up a set. Target system cable length:
• Allows the user to:
Set is user defined 14.0"
Run experiments
Opcode class editor allows user to create, 35.6cm
delete or edit Opcode classes Emulator and target system cable weight:
Examine/modify data 5.0Ibs.
• 14 functional capabilities: 2.2 kg
Run Examine/Modify Memory Emulator probe head:
Single-step Compatible with 24 lead 300 mil wide DIP
Reset on 100 mil centers
Disassemble
OS-Escape Single line assemble
Set pass count Examine/modify raw data
Set simple break and trace triggers Mapping Host Specification
Set repetition counter • Microcontroller internal memory operations: An IBM PC, PC XT, PC AT or 100%
Set phantom break and trace triggers Dump
Set trace triggers (start, end & center) compatible system with 640K bytes of RAM.
Scan and modify PC-DOS 2.0 or later.
View up to 4K of trace buffer Fill Two (2) floppy disk drives.
Examine/modify: Move One (I) RS232C interface card for the PC
Special Function Registers Search and cable,
Internal data memory Compare
Program memory Examine/modify addressable bits
warranty
Ninety (90) days limited warranty, parts and
labor.
Signetics
Signetics Company
MClaLink is a trademark of MctaLink Corporation. 811 E. Arques Avenue
PC-DOS, PC, PC XT and PC AT are trademarks of IBM.
IBM is a registered trademark of IBM Corporation P.O. Box 3409
Intel is a registered trademark of Intel Corporation Sunnyvale, California 94088-3409
fJMETALINK CORPORATION 1988 5--13 Telephone 408/991-2000
System Overview
Signetics-ASM51
8051 Macro
Cross Assembler
• IBM PC or 100% Compatible Host • Symbolic Access to Predefined Hardware

• Supports All Members of the MCS-Sl Family Registers
• Supports All S Memory Spaces • Fast Assembler Execution Time
• Uses Standard Mnemonics and Syntax • Full Range of Assembly Time Operators,
Complete Listing and Output Controls and
• Generates Intel HEX and MetaLink or choice of Radix
Signetics Debug Format for use with
Signetics emulators • INCLUDE Statement Allows Development of
Code In Modules
• Conditional Assembly and Full Macro
Capability including Nesting
PHILIPS 98-8270-050
5-14 l032-o00!688flM
Functional Description
The Signetics-ASM5! Macro Cross Assembler takes an assembly language source file created with a text editor and translates it into a machine language object
file. This translation process is done in two passes over the source file. The Signetics-ASM51 Macro Cross Assembler is supported on IBM PCs and as such
has faster assembly times than traditional methods. The Signetics-ASMS t Macro Cross Assembler supports modular code development or will assemble
previously developed code modules through the use of the INCLUDE capability that brings together these code modules at assembly time.
Products Supported Instructions Supported Conditional Assembly
8052 8051 80C51 • Standard mnemonics plus generic CALL/IMP. • IF-THEN-ELSE conditional capability, nested
8032 8031 80C31 up to 255 levels.
87C51
Assembly Time Operators
83C75 I 80C45 I Macro Capability
87C75 I 83C451 • Operations supported are: +, -, HIGH, LOW,
87C451 MOD, /, *, SHR, SHL, NOT. AND, OR, • Full macro capability exists with up to nine (9)
XOR, =, <, >, <>, <=, >=. levels of nesting.
80C552 80C652 • Operations are done in 16-bit 2's complement • Up to 16 parameters can be specified in a
83C552 83C652 arithmetic. macro.
87C552 87C652
Listing Controls Assembler Type

Symbols • Controls supported: Title, Date, List, Nobst, • Two (2) pass, absolute assembler.
• Symbols can be up to 255 characters long, with Paging, Nopaging, Eject, Pagelength and
the first 32 being significant Pagewidth.
• Symbols character set include: Minimum System Requirements
? and _ (underline)
A ... Z
An IBM PC, PC XT, PC AT or 100%
Output Controls compatible system with 96K bytes of RAM.
a ... Z
• Controls supported: Object, Noobject, Print, PC-DOS 2.0 or later.
0 ... 9
Noprint, Symbols, Nosymbols and Debug. One (I) ftoppydisk drive.
Numbers
Object File Format Warranty
• Numbers can be entered in decimal (default),
binary, hexadecimal or octal. • Standard Intel Hexadecimal Object Code Ninety (90) days free update service.
Format.
• MetaLink or Signetics Debug Format for use
with Signetics emulators.
Predefined Addresses
• All MCS-51 architecturally defined Special
Function Registers (SFR) are symbolically Include Capability
defined in the Signetics-ASM51 Macro Cross
Assembler. • Any number of files can be included in the
source file, nested up to eight (8) levels deep.
Memory Spaces Supported

• Code, Data, Bit, External and Indirect.
Signetics
Signetics Company
MetaLink is a trademark of MetaLink Corporation 811 E. Arques Avenue
PC-DOS, PC, PC XT and PC AT are trademarks of IBM. P.O. Box 3409
Intel is a registered Irademark of Intel Corporation. Sunnyvale, Califomia 94088-3409
©METALINK CORPORATION 1988 !'>-15 Telephone 408/991-2000
Universal EPROM Programmer
SPGM-100 EPROM Microcontroller

and Standard EPROM Programmer
FEATURES
o Supports standard EPROMs o Uses standard, intelligent and
o Modules Available for Micro- quick pulse programming algo-
controller Support rithms
lEt 87C751 o 8K x 8 Data Buffer Standard
lEt 87C752 (32K, 64K Optional)
lEt Others to follow o Supports Intel Hex Format
o Connects to IBM PC or 100% o System Includes Power Supply,
Compatibles RS-232 Cable, System Software,
Documentation and Programmer
PROGRAMMING
SITE
SPGM-100
SPGM-100 System Block Diagram
OPERATIONS
o Select EPROM Type
o Blank Check
o Program EPROM array
o Display!Alter Data Buffer
o Fill Buffer with Constant
o Copy EPROM to Buffer
o Verify EPROM Versus Buffer
o Error Display (Program/Verify)
o Help
5-16
Signetics
Signetics Section 6
Additional
Microcontroller
Data Sheets
INDEX
8X305 Microcontroller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 6-3
8X401 Microcontroller
SCN8049 Series. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 6-28
........................................ 6-48
Signetics 8X305
Microcontroller
FEATURES mum of 200ns. Within one instruction PIN CONFIGURATION

• Fetch, Decode, and Execute a cycle, the 8-bit data-processing path can N, I PACKAGES
16-bit instruction in a minimum be programmed to rotate, mask, shift,
of 200 ns (one machine cycle) and/or merge single or multiple bit sub-
• Bit-oriented instruction set fields and, in addition, perform an ALU
(addressable single-or-multiple bit operation. In the same instruction, an
subfields) external data field can be input, pro-
• Separate buses for Instruction, cessed, and output to a specified desti-
Instruction Address and Three- nation -likewise, single or multiple bit
State I/O data fields can be internally moved from
a given source to a given destination. To
• Thirteen 8-bit general-purpose
working registers summarize, fixed or variable-length data
fields can be fetched, processed, oper-
• Source/destination architecture
ated on by the ALU, and moved to a
• Bipolar low-power Schottky different location - all in a timeframe of
technology/TTL inputs and 200ns. To interface with I/O and pro-
outputs gram memory, the 8X305 uses a 13-bit
• On-chip oscillator and timing instruction address bus, a 16-bit instruc-
generation tion bus, an 8-bit bidirectional multi-
• Single + 5V supply plexed I/O data/address bus and a 5-bit
• 0.9-in. 50-pin DIP I/O control bus.
• 68-Pin PLCC A wide selection of I/O devices, inter-
face chips, and special-purpose parts
PRODUCT DESCRIPTION are available for systems use. In most
The Signetics 8X305 Microcontroller applications, the more powerful 8X305 is
(Figure 1) is a high-speed bipolar micro- functionally interchangeable with its pre-
processor implemented with low-power decessor-the 8X300.
Schottky technology. In a single chip,
the 8X305 combines speed, flexibility, ASSOCIATED DOCUMENTATION
and a bit-oriented instruction set. These Other documents directly relating to de-
features and other basic characteristics sign and applications use of the 8X305
of the chip combine to provide cost- Microcontroller are:
effective solutions for a broad range of • Product Capabilities Manual
applications. The 8X305 is particularly • 8X305 Users Manual
useful in systems that require high-
These documents and other current lit-
speed bit manipulations - sophisticated
erature (Data Sheets, Product Bulletins,
TOP view
controllers, data communications, very
fast interface control, and other applica- Applications Notes, etc.) are available at
tions of a similar nature. all Signetics Sales and Service Of-
fices - see rear cover of this data sheet
The 8X305 can fetch, decode, and exe- for the office in your locality.
cute a 16-bit instruction word in a mini-
DESCRIPTION ORDER CODE
50-Pin plastic DIP N8X305N
50-Pin ceramic DIP N8X3051
68-Pin PLCC N8X305A
December 17, 1986 6-3 853-0925 086958

(/}
0
CD
0
CD
3
s:
o·
<C-
::J
~
0-
a
~
a
0
:;;::
ri-
-"" PROGRAM COUNTER o::J i3
CD ... leyend: u
CD • _ DATA DATA REGISTERS - Not. . 11t1 ~Vcc -+ i3
0> A,
A,
o_ ~~~~~: AND ADDRESS G G I(N~::2)! --<D-VCII
a ~
0
~ -. :::~:~g~:g= ~~~TROL
--@-Vlt
A,
... G!(N:::3i! .n
G CD
....
...
H _ ~~~:~~EXTERNAL
(Nole 3) -®-GND -u
i3
G ~ I (N:I~2) I Q.
c
a
A,
... 8G28
.
A"
Au
Au
iVO
JV1
M
'"
r
oj:> ~~[i~ 'l:J-(:t.L-J. I .
-----
I
~Jrt±-
~ •
38
jliM
iV'3
IV.
Wi
.w
sc
we
' '=H
,"
'12
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.ESET
NOTES:
1. Registers R1-R6, All and A14-R16 are general-purpose working registers.
2. In any instruction where R7 (IVL) or Rll (IVA) is specified as the destination, the a-bit value is output on the IV bus as an IV device enable address (SC "" High) - R7 = left bank and Rll = right bank; the results are also stored into the -u
specified internal register and may later be accessed as source data.
3. R12 and R13 are general-purpose working registers for all operations except transmit (XMIT).
8.c
4. The feast significant bit of register R10 (OVF) is used to reflect the carryout status resulting from the most recent ADD operation. Q.
5. Auxiliary register RO # 1 is a general-purpose working register that holds the implied operand for Arithmetic and Logical operations; the content of this register is repeated in AUX # 2 (shown dotted). The duplicate register is physically
part of the ALU and is shown separate only for layout convenience. 00 ~o
6. Internal working registers cannot be operated on by the MASK logic.
'*
7. During NZT instructions the ALU tests for all bits equal to "0" (Transfer if A 0) -refer to BASIC OPERATIONS that follow. ><
W 3;
Figure 1. Architecture and· Pin Designations for 8X305 Microcontroller o S.(5-

Pin Numbers Shown are for DIP Packaging 01
::J
M icrocontroller 8X305
VCRQ
"Q
.. [1
~VR
~
~ ..
..
.. ~ ~"'10
.. [! ~Al1
A3~ ~Al1
A2[! ~HALT INDEX
Al~ 19 RESET
CORNER
9 1 61
.. [! ~MCLK
X1§ ~iYO 10 0 60
X2~ ~iV1
GND@
~iV2
~~ ~iVa PLCC
11~ ~vcc
12@ ~iV4
la§ ~iVs 26 44
I.~ ~iVi
15~ ~M
27 43
.@
11~
~RB
!!lUi
TOP VIEW
COOO68PS
I.~ ~wc
,,~ ~sc
hO~ ~115
111~ !!1h4
112~ ~113
CD09<l61S
PLCC DIP
IDENTIFIER FUNCTION
PIN NO. PIN NO.
1, 68 1 VCR Regulated voltage input from series-pass transistor (2N5320 or equivalent).
4-11,62-66 2-9, 45-49 Ao-A12 Program Address Lines: These active-high outputs permit direct addressing of up to 8192 words
of program storage; A12 is least significant bit.
12, 13 10, 11 Xl, X2 Timing generator connections for a capacitor, a series resonant crystal, or an external clock
source with complementary outputs.
2,3, 14-16 12 GND Ground.
17-23, 13-28 10 -115 Instruction Lines: These active-high input lines receive l6-bit instructions from program storage;
28-36 115 is least significant bit.
37 29 SC Select Command: When high (binary 1), an address is being output on pins IVO through IV7.
38 30 WC Write Command: When high (binary 1), data is being output on pins IVO through IV7.
39 31 LB Left Bank Control: When low (binary 0), devices connected to the Left Bank are accessed. (Note:
Typically, the LB Signal is tied to the ME input pin of 110 peripherals).
45 32 RB Right Bank Control: When low (binary 0), devices connected to the Right Bank are accessed
(Note. Typically, the RB signal is tied to the ME input pin of liD peripherals).
December 17, 1986 6-5

PLCC DIP
IDENTIFIER FUNCTION
PIN NO. PIN NO.
46-49, 33-36, IVO-IV? Interface Vector (Input/Output Bus) - these bidirectional active-low three-state lines
55-58 38-41 communicate data and/or addresses to I/O devices and memory locations. A low voltage level
equals a binary "1"; IV? is Least Significant Bit.
50-52 3? Vcc + 5Vpower supply.
59 42 MCLK Master Clock: This active-high output signal is used for clocking I/O devices and/or
synchronization of external logic.
60 43 RESET When RESET input is low (binary 0), the 8X305 is initialized - sets Program Counter/Address
Register to zero and inhibits MCLK. For the period of time RESET is low, the Left Bank/Right Bank
(IJ3IRB) Signals are forced high asynchronously.
61 44 HALT When HALT input is low (binary 0), internal operation of the 8X305 stops at the start of next
instruction; MCLK is not inhibited nor is any internal register affected. However, both the Left
Bank/Right Bank (LB/RB) signals are synchronously driven high during the first quarter of the
instruction cycle time and remain high during the time HALT is low.
6? 50 VR Internally-generated reference output voltage for external series-pass regulator transistor.
24-2?, - No Connect
40-44,
53, 54
NOTE:
Multiple Vcc, GND, and VCA pins must be externally connected.
Figure 2. Designations and Descriptions for Pins of 8X305 Microcontroller.
December 17. 1986 6-6

Microcontroller 8X305
FUNCTIONAL OPERATION words of program storage - either ROM or simple method of implementation is shown in
PROM. The user interface (IVO through IV7) is Figure 3. When LB is active low, the left bank
Typical System Configuration capable of uniquely addressing 256 Input! is enabled and anyone of 256 locations
Although the system hookup shown in Figure Output locations and, with additional bank within the RAM memory can be accessed for
3 is of the simplest form, it provides a bits (LB, RB), this number is expanded to input! output operations. A similar set of "en-
fundamental look at the 8X305 Microcontral- 512 - each bank comprising 256 addressable/access" conditions are applicable to the
ler and peripheral relationships. As indicated, able locations. The addressable locations of right bank when RB is active low.
the 8X305 can directly address up to 8K each bank can be used in a variety of ways; a
LeQand:
• =110 DATA AND ADDRESS
Wi; - INSTRUCTION ADDRESS
0, = INSTRUCTION
USER
) CONTROLLED
INPUTS
a: 8X450 RAM
w (258.8)
-'
-'
PROGRAM STORAGE
o
(READ ONLY MEMORy)
X2 ",a:
01-
8K)C 18 ROMIPROM GND ..,Z
><0
<0(,)
o
a:
LEFT BANK
(,) RIGHT BANK

i
1-0F·258
I/'.'---::---I~ ADDRESSABLE
LOCA110NS
Figure 3. Typical 8X305 System Hookup
December 17, 1986 6-7

BASIC OPERATIONS OF 8X305

Refer to a later discussion of "Instruction Fields" for a detailed examination of ali operand fields and subdivisions thereof - "S" (So, S1), "0"
(Do, 0 1), "R", "L", "J", and "A".
MOVE OPERATIONS
I---------------REGISTER-TO-REGISTER--------------
SOURCE DATA PROCESSING ALU DATA PROCESSING DESTINATION
(PRE-ALU) (POST-ALU)
RD-R 1? as specified by _ Right rotate as specified r. No operation. No operation. RD-R?, R11-R17 as
"8" field of instruction. by "R" field of specified by "0" field of
instruction. instruction.
1 - - - - - - - - - - - - - - - - REGISTER-TO·W BUS - - - - - - - - - - - - - - - -
RD-R17 as specified by _
"8" field of instruction.
No operation. _ No operation. r- Shift and merge as
specified by "Do" and
- Variable length field of iV
bus - Left Bank (03) or
"L" fields of instruction. Right Bank (RB) as
"01" fields of instruction.
I - - - - - - - - - - - - - - - I V BUS-TO-REGISTER - - - - - - - - - - - - - - -
-
Variable length field of iV _ Right rotate and mask ,.. No operation. No operation. RD-R?, R11-R17 as
bus - Left Bank (03) or as specified by "So" and specified by "0" field of
Right Bank (RB) as ilL" fields of instruction. instruction.
specified by "S,' and
"SO" fields of instruction.
1---------------- IV BUS-TO-IV BUS

-
Variable length field of iV

r- Right rotate and mask
as specified by ,r So " and
r- No operation. Shift and merge as
.... Variable length field of iV
Right Bank (RB) as ilL" fields of instruction. "L" fields of instruction. Right Bank (RB) as
specified by "S,' and specified by "Do" and
"So" fields of instruction. "0 1" fields of instruction.
December 17, 1986 6-8

ADD OPERATIONS
REGISTER-to-REGISTER -..ISOURCEI-..lpRE-ALUf--1 I~POST-ALUI-"1 DEST 1
REGISTER-to-IV BUS -"ISOURCEI-"lpRE-ALU~_1

Same as MOVE operations, except source
data is ADDed to contents of AUXiliary l~ POST-ALU 1-..1 DEST 1
Register RO via the ALU; if appropriate,
IV BUS-to-REGISTER -"ISOURCEI-"lpRE-ALU~_1 Overflow Register RIO (OVF) is also set. I~POST-ALUI-"1 DEST 1
IV BUS-to-IV BUS -..ISOURCEI-..lpRE-ALUf--1 I~POST-ALUI-"1 DEST 1
AND OPERATIONS
REGISTER-to-REGISTER -..ISOURCEI-..lpRE-ALUf--1 l~ POST-ALU 1-..1 DEST 1

REGISTER-to-IV BUS -..ISOURCEI-..lpRE-ALUf--1
data is ANDed with contents of AUXiliary l~ POST-ALU 1-..1 DEST I
Register RO via the ALU.
IV BUS-to-REGISTER -..ISOURCEI-..lpRE-ALUf--1 I~POST-ALUI-"1 DEST 1
IV BUS-to-IV BUS -..ISOURCEI-..lpRE-ALUf--1 l~ POST-ALU 1-..1 DEST 1
EXCLUSIVE OR (XOR) OPERATIONS
REGISTER-to-REGISTER -..ISOURCEI-..lpRE-ALUf--1 I~POST-ALUI-"1 DEST 1

REGISTER-to-IV BUS -..ISOURCEI-..lpRE-ALUf--1 data is Exclusively ORed with contents of I~POST-ALUI-"1 DEST 1
AUXiliary Register RO via the ALU.

IV BUS-to-REGISTER -..ISOURCEI-..lpRE-ALUf--1 I~POST-ALUI-"1 DEST 1
IV Bus-to-IV BUS -..ISOURCEI-..lpRE-ALUf--1 I~POST-ALUI-"1 DEST 1
EXECUTE (XEC) OPERATIONS
XEC, REGISTER
- - -
RO - R17 as specified by
"S" field of instruction.
No operation. Add source data to 8-bit
field specified by
No operation. r- Replace 8 LSB of
Address Register with
instruction literal 8-bit sum from ALU.
(0 < J < 377.).
• PG M eTR unchanged.
XEC, IV BUS
- - -
Left or Right Bank of 117 Rotate and mask as Add masked field of No operation. I- Replace 5 LS~ of
bus as specified by "S" specified by "So" and source data to 5-bit Address Register with
field of instruction. "L" fields of instruction. literal specified by "J" 5-bit sum from ALU.
field of instruction
(0 <J <37.). 'PGM eTR unchanged.
December 17, 1986 6-9

NON-ZERO TRANSFER (NZT) OPERATIONS
NZT, REGISTER
SOURCE DATA PROCESSING ALU DESTINATION
- -
(PRE-ALUl
RO-R17 as specified by
"S" field of instruction. - No operation. Test contents of source
register for all zeroes.
- - - - - - If S = 0, increment PC
by 1; if S*O, replace 8
LSB of AR and PC with
literal specified' by "J"
field of instruction.
NZT, W BUS
SOURCE DATA PROCESSING ALU DESTINATION
-
(PRE-ALUl
Left or Right Bank of iV

bus as specified by "S"
- Rotate and mask as
specified by "So" and
"L" fields of instruction.
Test contents of masked
field for all zeroes. --- --- - If S = 0, increment PC
by 1; if S *0, replace 5
LSB of AR and PC with
literal specified by "J"
TRANSMIT (XMIT) OPERATIONS

I XMIT, REGISTER
-
(PRE-ALUl (POST-ALUl
0 .. J .. 3778 - value
specified by "J" field of
>. No operation. No operation. r- No operation. r- RO-R7, R11, R14-R1·7.
Load a-bit integer
instruction. specified by "J" field
into register specified by
"0" field.
XMIT 8-BIT IMMEDIATE, W BUS

0 .. J .. 3778 - value
r- No operation. r- No operation. r- No operation. r- Left (R12) or Right (R13)
Bank of iV bus as
instruction. specified by "0" field of
instruction.
XMIT VARIABLE-BIT FIELD IMMEDIATE W BUS
- -
o .. J .. 378 - value
r- No operation, r- No operation. Shift and merge source
data as specified by
Left or Right Bank of iV
bus as specified by "0"
instruction. "00" and "L" fields of field of instruction.
instruction.
December 17, 1986 6-10

Table 1. tion, anyone or all of the functions (Rotate/

Mask/Shift/Merge) can operate on 8 bits of
LB RB FUNCTION data in a single instruction cycle. For a
Low Low This state is not generated by the 8X305. summary of all data-processing capabilities,
refer to BASIC OPERATIONS OF THE 8X305
Low High Enable left bank devices. described earlier in this data sheet.
High Low Enable right bank devices. Instruction Cycle
High High Disable all devices; IV bus is 3-State. Each operation of the 8X305 is executed in a
single instruction cycle. The instruction cycle
is internally divided into four equal parts-
Table 2. each part being as short as 50ns. Figure 4
LB/RB SC WC FUNCTION shows the general functions that occur during
each quarter cycle; specifics regarding mini-
High Low Low The IV bus is 3-State and not looking for mum/maximum timing and other critical val-
input data. ues are described later in this data sheet.
Low Low Low The IV bus is reading input data. During the first quarter cycle, a new instruc-
tion from program storage is input via 10 - 115
Low Low High Data is being output. and decoded. If an I/O operation is indicated,
Low High Low Address is being output. new data is fetched from a specified internal
register or via the TV bus. At the end of the
X High High This condition is never generated. first quarter cycle, the new instruction is
Program Storage Interface both LB and RB are high (inactive), neither latched into the instruction register.
As shown in Figure 3, program storage is bank is enabled and the TV bus is inactive In the second quarter cycle, the I/O input
connected to output address lines Ao through (three-state). A functional analysis of the Left data stabilizes and preliminary processing is
A12 (A 12 = LSB) and input instruction lines 10 and Right Bank signals is shown in Table 1. completed. At the end of this quarter, the TV
through 115. An address output on Aol A12 Both data and I/O address information are latches close and final processing can be
identifies one 16-bit instruction word in pro- multiplexed on the TV bus. The SC (Select accomplished, thus completing the input
gram storage. The instruction word is subse- Command) and WC (Write Command) signals phase of the instruction cycle. During the third
quently input on 10/115 and defines the Micro- distinguish between data and I/O address quarter cycle, the address for the next in-
Controller operation which is to follow - one information as shown in Table 2. struction is output to the instruction address
instruction word equals one completed opera- bus, TV control signals are generated, and
tion. Any TIL-compatible memory can be Data Processing both data and destination are setup for the
used for program storage provided the worst- Basically, the data processing path of the remainder of the output phase. During the
case access time is compatible with the 8X305 consists of the Rotate/Mask logic, the fourth quarter cycle, a master clock signal
instruction cycle time used for the applica- Arithmetic Logic Unit (ALU), the Shift/Merge (MCLK) generated by the 8X305 is used to
tion - see timing section for appropriate cal- functions, on-chip memory (sixteen 8-bit reg- latch either the I/O-enabling address or the
culations. isters), and the bidirectional TV bus interface I/O data into peripheral devices connected to
with its associated driver circuits and internal the TV bus. MCLK can also be used to
I/O Interface and Control latches. The on-board memory and the TV bus synchronize any external logic with timing
An 8-bit bidirectional I/O bus, referred to as are connected to both inputs and outputs of
the Interface Vector (TV) bus, provides a circuits of the 8X305. To summarize the
the ALU via internal 8-bit data paths - see action, the first half of the instruction cycle
communication link between the Microcon- Figure 1. Inputs to the ALU are preceded by
troller and the two banks of I/O devices. The deals primarily with input functions and the
right-rotate and data-mask functions; the ALU second half is mostly concerned with output
LB (Left Bank) and RB (Right Bank) control output is followed by the left-shift and merge
signals identify which bank is enabled; when functions.
operations. Depending on the desired opera-
December 17, 1986 6-11'

INSTRUCTION SET
"II- OUTPUTPHASE~ General Format and Operating
----.r
r--INPUTPHASE
Principles
.J ~I_ _--' The 16-bit instruction word (10 through 115)
I 101 I 2nd I 31d I 41h I from program storage is input to the instruc-
j-4-QUARTER--f--QUARTER~QUARTER~QUARTER~
sons SOnl SOna SOns tion register (Figure 1) and is subsequently
INPUT LATCH AND NEXT LATCH I/O decoded to implement the events to occur
INSTRUCTION, PROCESS INSTRUCTION ENABLING during the current instruction cycle.
DECODE INPUT DATA ADDRESS, ADDRESS OR
INSTRUCTION GENERATE 110 DATA INTO The general format for each instruction word
AND, IF CONTROL SELECTED
REQUIRED, SIGNALS, AND PERIPHERAL. is shown in Table 3.
FETCH NEW SETUP 1/0
DATA DATA FOR The 3-bit operation code (OPCODE) define
OUTPUT anyone of eight classes of instructions;
~~-------------~If- IICLK IL
variations within each class are specified by
the remaining thirteen operand bits. The eight
(ACTIVE--I
STATE)
instruction classes can be separated into two
control areas - data and program; general
functions within these areas are as shown in
NOTES:
1. New instruction must be accepted and latched at end of first quarter cycle.
Table 4.
2. The 1/0 data latches are open for the first two quarter cycles, that is, for 1DOns.
3. The address changes during third quarter cycle. Instruction Fields
4. iV bus drivers are active (turned on) during third and fourth quarter cycles. As shown in Table 5, each instruction word
consists of an operation code (OPCODE)
Figure 4. Instruction Cycle and MCLK with: Crystal = 10MHz and
Cycle Time = 200ns. field and from one to three operand fields.
The possible operand fields are: Source (S),
Destination (D), Rotate/Length (R/L), Literal
(J), and Address (A). The OPCODE and
Table 3.
operand fields are described in the para-
! MSB LSB ! graphs that follow the table.
BIT POSITIONS --> 3 4 678 10 11 12 13 14 15
OPERAND(S)
Table 4.
• Data Control-
ADD
AND Arithmetic and Logic Operations
XOR 1
MOVE
XMIT
1Movement of Data and Constants
• Program Control-
XEC
NZT
1 Branch or Test
JMP
December 17, 1986 6-12

Table 5. Functional Description of Instruction Set

STATE OF CONTROL SIGNAL
DURING INSTRUCTION CYCLE
SEE FIGURE 4
-
INSTRUCTION WORD DESCRIPTION
CONTROL
INPUT PHASE OUTPUT PHASE
SIGNAL
CLASS = MOVE OPCODE =0 OPERATION = (5) ~

D
Reglster-ta-Register Move content of internal register specified by 5e L H if D-07., 17.
~!c:o~: 1,01"1'21~HI5!
5-field to internal register specified by D-field. we L L
1 1 3141 : 1617181: Prior to the "MOVE" operation, right-rotate
contents of internal source register by octal Ui H L if D-07.
5-00.-17. D-00.-07., 11.-17. value (0 through 7) defined by the R-field. ~ H L if D-17.
Register·to-IV Bus (Note) Move contents of internal register specified by SC L L
1 0 1'12131415161718191'01"1'21'31'41'51 the 5-field to the iV bus. Before outputting on we L H
iV bus, data is shifted as spec~ied by the least
IopeODE I 5 L D I I significant octal dign of the D-field and the bits LB L if D-20.-27. LifD-20.-27.
I I D, Do I specified by the L-field are merged with the
latched 110 data.
liB L il D-30.-37. L if D-30.-37.
5-00.-17. D-20.-37.
IV Bus-ta-Reglster (Note) Move right-rotated iV bus (source) data SC L H H D=07., 17.
1 0 1'12131415161718191'01"1'21'31'41'51 specified by the 5-field to internal register we L L
I opeODE 5I L I
D
specified by \he D-field. The L-field specHies
the length of source data starting from the Ui Lit 5-20.-27. LHD-07.
5, I So
5=20.-37. D=00.-07., 11.-17.
I I I L5B-position and, if less than B bits, the
remaining bits are filled w:ith zeros.
"FiB L H 5-30.-37. L H D-17.
IV Bus-ta-IV Bus (Note) Move right-rotated iV bus (source) data SC L L

101'12131415161718191'01"1'21'31'41'51 specified by the 5-fietd to the 110 latches. we L H
Before outputting on 1i7 bus, shift data as
10PCODE 5 I L D I I I specified by the D-field; then merge source Ui L if 5 = 20.-27. L H D-20.-27.
5,I So I L D, Do I end latched 110 data as specified by the L "1m L H 5-30.-37. L H D - 30.-37.
(length) field.
5 - 20.-37. D-20.-37.
CLASS = ADD OPCODE =1 OPERATION = (S) + (AUX) ~ 0
Same as MOVE instruction class Same as MOVE instruction class except that Same as MOVE instruction class
contents of AUX (RO) register are ADDed to
the source data. If there is a "carry" from
MSB, then RIO (OVF) = 1 (overflow),
otherwise OVF = O.
CLASS = AND OPCODE =2 OPERATION = (5) /\ (AUX) --+ 0
contents of AUX (RO) register are ANDed
with source data.
CLASS = XOR OPCODE =3 OPERATiON = (5) Ell (AUX) --+ 0
contents of AUX (RO) register are Exclusively
ORed with source data.
CLASS = XEC OPCODE =4 OPERATION = Refer to Description
Register Immediate Execute instruction at current page address SC L L
oIIset by J (literal) + (5). Return to normal
1 ~!e~~: 1 3141 : 1617IBI9110111!'21'3HI5! instruction flow unless a branch is
encountered.
we
LB
L
H
L
H
Execute instruction at an address determined
S - 00.-17. J-000.-377. by replacing the low-order B bits of the RB H H
Address Register with the following derived
sum:
Value of Ineral (J-field) plus contents of
internal register specified by S-field
The PC is not incremented and the overflow
status (OVF) is not changed.
IV Bus Immediate (Note)
Execute instruction at an address determined
1 0 1'12131415161718191'01"1'21'31'41'51 by replacing the low-order 5 bits of Address 5e L L
I OPCODE 5I L I
J Register with the following derived sum: we L L
I s, So I I I 5-b~ value of literal (J-field) plus value of
rotated source data specified by S-field.
The L-field specifies the length of source
LB L if 5- 203-27. H
5=20.-37. J-00.-37. RB L if 5-30.-37. H
data starting from the LSB position and, if
less than B bits, the remaining bits are filled
with zeros; the Program Counter is not
incremented and the overflow status (OVF)
is not changed.
December 17, 1986 6-13

Table 5. Functional Description of Instruction Set (Continued)
STATE OF CONTROL SIGNAL

DURING INSTRUCTION CYCLE
SEE FIGURE 4
-
INSTRUCTION WORD DESCRIPTION
CONTROL
INPUT PHASE OUTPUT PHASE
SIGNAL
CLASS = NZT OPCODE =5 OPERATION = Refer to Description

Register Immediate se L L
If data specified by the 8-field is not equal to
1 ~le~l: 1 3141 : 161718191101ll~12113H151 zero, jump to current page address offset by
value of J~field; otherwise, increment the
we
LB
L
H
L
H
Program Counter.
S~00.-17. J ~ ODD. - 377. RB H H
If contents of internal register specified by S-
field is non-zero, transfer to address
determined by replacing the low-order 8 bits
of Address Register and Program Counter
with "J", otherwise, increment PC.
IV Bus Immediate (Note)

If right-rotated and masked IV bus is nan-
D 11 I2 31 4 1 5 1 6 1 7 81 9 110 11112113114115 zero, transfer to address determined by 5C L L
OPCODE 5 L J replacing low-order 5 bits of Address WC L L
Register and Program Counter with "J",
5, 50 otherwise, increment PC. (The L-field LB L if S=208-278 H
5 ~ 20.-37, J ~ 00, - 37. specifies the length of source liD data RB L if 5~30,-37, H
starting from the LSB-position and, if less
than 8 bits, the remaining bits are filled with
zeros.)
CLASS = XMIT OPCODE =6 OPERATION =J ~

D
XMIT, Register 5e L L
Store a-bit value specified by "J" into
1 ~le~l: 1 3141 ~ 161718191101ll~12113H15i register specified by "D". we

LB
L
H
L
H
D~00,-06,. 11,. 14.-16. J ~ ODD. - 377. RB H H
XMIT, IV Bus Address
Enable 110 device on the bank specified by
8e L H
oj 1"[2 1
31 4 1 5 6 J7 8 J 9 LlO 11112]13114]15 "0". whose address is the 6-bit integer
specified by "J". Address "J" is stored in
we L L
OPCODE D J LB H L if D~07,
register "0".
D = 078. 178 J ~ 000,-377. RB H L if D~17.
XMIT 8 Bits Immediate, IV Bus (Note)

Store value of a-bit integer in the previously
SC L L
o 11 12 31 4 1 5 1 6 1 7 819110 111121131141151 enabled 110 port, at the bank destination ([8 WC L H
or RB) specified by "0". Contents of R12 or
OPCODE D J LB H LifD~12.
R 13 remain unchanged.
D~12.-13. J ~ ODD. - 377, RB H L if D~13,
XMIT Variable Bit Field Immediate, IV Bus (Note)

Transmit Least SignificE!!:!.t "L" bits of "J"
5C L L
011 12 31 4 1 5 1 6 1 7 8 19110 11112113114115 field to "L-bit" field of IV bus specified by WC L H
"0"; if "L" is greater than 5 bits, the M8B
OPCODE D L J LB L if D~20,-27. L if D-20.-27.
bits of destination field is filled with zeros.
D, Do RB L if D~30,-37. L if D-30,-37.
D - 20.-37. J-00.-37.
CLASS = JMP OPCODE =7 OPERATION = Refer to Description

Address Immediate 8C L L
Jump to address in program storage
1 0 11 1213141s1617161elfOlni12113H1Si specified by A-field; this address is loaded WC L L
into the Address Register and the Program
OPCODE A LB H H
Counter.
A ~ 00000, - 17777. RB H H
NOTE:
So specifies the L8B of rotated input data field
81 specifies the bank of iV bus from which source data will be input
00 specifies bit position in 1/0 device with which L8B of processed data will be aligned, and
0 1 specifies the bank of iV bus which will be the destination.
December 17, 1986 6-14

Table 6. Octal Addresses and Source/Destination Fields for 8X305 Registers

DESTI· DESTI·
ADDRESS REGISTER DESIGNATION SOURCE ADDRESS REGISTER DESIGNATION SOURCE
NATION NATION
RO (AUX) - General R10 (OVF-Overflow
008 X X 108 X
purpose register register)
R1-General purpose R11 - General purpose
01 8 X X 118 X X
register register
R2-General purpose R12-General purpose
02 8 X X 128 X X
register register (Note)
R3-General purpose R 13 - General purpose
03 8 X X 13 8 X X
register register (Note)
R4-General purpose R 14 - General purpose
048 X X 148 X X
register register
05 8 X X 158 X X
register register
068 X X 168 X X
register register
R7 - Special purpose R17 - Special purpose
07 8 register (refer to next X X 17a register (refer to next X X
paragraph) paragraph)
NOTE:
R12 and R13 function as general purpose working registers for all operations except transmit (XMIT). During a transmit instruction where R12 or R13 is the
destination, the a-bit "J" field is immediately transferred to the TV bus; for this operation, the contents of the designated register remain unchanged.
Operations Code Field. The 3-bit OPCODE

field specifies one of eight classes of 8X305 DESIGNATES LEFT DESIGNATES LSB OF
instructions; octal designations for this field (2) OROF
BANK RIGHT (3)~ ~1I0
ill BUS DATA-REFER
TO TEXT DESCRIPTIONS
and operands for each instruction class are
shown in Table 5. S, So :l
OR OR IE
0, Do
Source (S) and Destination (D) Fields. The 10111213141518171
5·bit "S" and "D" fields specify the source
and destination, respectively, for whatever
operation is defined by the OPeration CODE.
The "S" andlor "D" fields can specify an
20a
21.
22a
ttl
internal 8X305 register or any one-to-eight bit 23e
field within an 1/0 device; octal values and 24a
25a
sourcel destination field assignments for all
280
internal registers are shown in Table 6. 278
In instructions where R7a (IVL) or R17a (IVR)
is specified as the destination, the 8-bit value NOTES:
is output on the iV bus as an 110 device 1. The field length of O-to-8 bits is specified by the "L" field.
2. For the Right Bank, 308 - 378 perform equivalent 110 functions.
address or memory location; register R7 se-
lects the Left Bank and register R 17 selects
the Right Bank. The results are also stored
RIGHT·ROTATE FUNCTION
into the specified internal register (R78 or
R178) and may later be accessed as source 2 3 4 567
data. When the iV bus is specified as a
source and lor destination, the "S" and "D"
fields are split into two parts, that is,
• Source (S) = S1, So and Destination
(D) = D1, Do where,
Rotate (R) and Length (L) Field. The 3-bit of the data specified in the "S" field (see
So specifies the LSB of rotated input
R/L field performs one of two functions, accompanying diagram.) The source-register
data field
specifying either the field length (L) for I/O data (up to 8 bits) is right-rotated during the
S1 specifies the bank of iV bus from
operations or a right-rotate (R) for internal "input phase" of the instruction cycle (Figure
which source data will be input
operations. For a given instruction, the speci· 4). This function is always performed prior to
Do specifies bit position in 1/0 device
fied funr.tion depends upon the contents of any ALU operation. (Note: The right-rotate
with which LSB of processed data will
the Source (S) and Destination (D) fields. function is implemented on the bus and not in
be aligned and
the source register.)
D1 specifies the bank of iV bus which When an internal register is specified by both
will be the destination. the source and destination fields, the "R" When either or both of the source and desti-
field is invoked and it specifies a right-rotate nation fields specify a variable·length I/O
December 17, 1986 6-"\.5
data field, the" L" field specifies the length of

the I/O data field (see following diagram). If 01234567
the source field specifies an IV address
(20e - 37 e) and the destination field specifies IIIIIIII
an internal register (00e-07e, 11a-17a), the I I I I I I I ~1<------L=1
"L" field specifies the length of source data;
the source data is formed by right-rotating the I I I I I I I< L=2
IV bus data according to the source address I I I I I I< L=3
and then masking result as specified by the
"L" field. If length is less than 8 bits, all
I I I I I( L=4
remaining bits are set to zero prior to pro- I I I I< L=5

cessing data in the ALU. If the source field I I I< L=6
specifies an internal register (OOa - 17a) and
the destination field specifies IV bus data I I< L=7
(20e - 37e), the" L" field specifies the length I< L=O
of the destination data. To form the destina-
tion data, the ALU output is left-shifted ac- IV DATA LENGTH SPECIFICATION
cording to the destination address and then (No Rotate Function Specified)
masked to the required length (see IV DATA
LENGTH SPECIFICATION). The destination A Field. The 13-bit "A" field is an address source/destination addresses are specified
data is merged with data in the I/O latches to field which allows the 8X305 to directly using a 5-bit code (OOa - 37 8), When the most
finalize the IV bus data. Hence, a one-to-eight branch to any of the 8192 locations in Pro- significant octal digit is a "0" or "1", the
bit destination data field can be inserted into gram Storage memory. source and/or destination address is an inter-
the existing 8-bit I/O port without modifying nal register; if the most significant digit is a 2
surrounding bits. If both the source and desti- Formation of Instruction or 3, an IV bus operation is indicated - 2
nation fields specify IV bus data (20e - 37 a), Address specifying a Left-Bank (LB) operation and 3
the "L" field specifies the length of both the The Address Register and Program Counter specifying a Right-Bank (RB) operation. The
source and destination data. are used to generate addresses for acceSSing least significant octal digit (0 through 7)
an instruction from program storage. The indicates either a specific internal register
To form the source data, the IV bus input data
instruction address is formed in one of the address or positioning information for the
is right-rotated according to the source ad-
following ways: least significant bit when specifying IV bus
dress and then masked to the required
• For all except the JMP, XEC, and a data. Referring to Table 5, AUXiliary register
length-see IV DATA LENGTH SPECIFICA-
"satisfied" NZT instruction, the Program RO (008) is the implied source of the second
TION. If length is less than 8 bits, all remain-
Counter is incremented by one and argument for the ADD, AND, and XOR opera-
ing bits are set to zero before processing in
placed in the Address Register. tions. IVL register R7 and IVR register R 17
the ALU. To form the destination data, the
ALU output is left-shifted according to the • For the JMP instruction, the 13-bit "A" (destination addresses 078 and 17a, respec-
destination address and masked to the re- field contained in the JMP instruction tively) provide a means of routing enabling
quired length specification. The destination word replaces the contents of both the address information to I/O peripherals. With
data is then merged into the IV bus data that Address Register and the Program IVL or IVR specified as the destination ad-
was used to obtain the source; thus, if the Counter. dress, data is placed on the IV bus during the
source and destination addresses are on the • For the XEC instruction, the Address output phase of the instruction cycle; simulta-
same bank, the IV bus data written to the Register is loaded with bits from the neously, a Select Command (SC) is generat-
destination I/O Port appears unmodified, ex- Program Counter modified as follows: ed to inform all I/O devices that information
cept for bits changed during the shift-and- XEC using IV Bus Data - low-order 5 on the IV bus is to be considered as an I/O
mask operations. If the source and destina- bits of ALU output replaces counterpart address. Since the contents of IVL and IVR
tion addresses refer to different banks, the bits in Address Register. are preserved, either register may later be
destination I/O Port is changed to contain the accessed as a source of data.
contents of the source 110 Port in those bit XEC using Data from Internal Register-
Control outputs LB and RB are used to
positions not affected by the destination data. low-order 8 bits of ALU output replaces
partition I/O bus devices into two fields of
counterpart bits in Address Register. 256 addresses. With LB in the active-low
J Field. The 5-bit or 8-bit "J" field is used to
load a literal value (coritained in the instruc- The Program Counter is not modified for state and a source address of 20a - 27 a, the
tion) into a register, into a variable I/O data either of the above conditions. left bank of I/O devices are enabled during
field, or to modify the low-order bits of the • For a "satisfied" NZT instruction, the the input phase of the instruction cycle. With
Program Counter. The bit length of the" J" low-order 5 bits (NZT source is IV bus RB in the active-low state and a source
field is implied by the "S" and "L" fields in data) or low-order 8 bits (NZT source is address of 30 a - 37 a, the right bank of de-
the XEC, NZT, and XMIT instructions, based an internal register) of both the Address vices are enabled. During the output phase,
on the following conditions: Register and Program Counter are LB is low if the destination address is 07 a or
• When the Source (S) field specifies an loaded with the literal value specified by 20a - 27 a, whereas RB is low if the destina-
internal register, the literal value of the the "J" field of instruction word. tion address is 17a or 30 a - 37 a. Each ad-
"J" field is an 8-bit binary number. dress field (LB and RB) can have a different
Data Addressing I/O device selected, that is, data can be
• When the Source (S) field specifies a The source and/or destination addresses of
variable I/O data field, the literal value transferred from a device in one bank to a
the data to be operated upon are specified as device in the other in one instruction cycle.
of the "J" field is a 5-bit binary part of the instruction word. As shown earlier,
number.
December 17, 1986 6-16
PARAMETER CONDtTIONS LIMITS
hie VCE:2V; > 50

100mA < Ie < SOOmA
VB EON VCE=5V; Ie = 500mA < 1V

aX30S
VCESAT IC=500mA; IB=50mA < O.SV
T 1I'F. V_CR
:r:-::-. BVCEO > 15V
't > 30MHz
NOTE:
Typical approved parts - 2N5320, 2N5337
Voltage Regulator
DESIGN PARAMETERS VOLTAGE REGULATOR

Hardware design of an 8X305-based system All internal logic of the 8X305 is powered by
largely consists of the following operations: an on-Chip voltage regulator that requires an
• Selecting and interfacing a Program external series-pass transistor. Electrical
Storage device - ROM, PROM, etc. specifications for the off-chip power transistor
• Selecting and interfacing input! output and a typical hook-up are shown in the
devices - RAM, Ports, and other B-bit accompanying diagram. To minimize lead
addressable I/O devices. inductance, the transistor should be as close
as possible to the 8X305 package and the
• Choosing and implementing System
Clock - Capacitor-Controlled, Crystal- emitter should be AC-grounded via a 0.1 Ilf
Controlled, or Externally-Driven. ceramic capacitor.
• Selection of an off-chip series-pass All information required for easy implementa-

transistor. tion of these design requirements is provided
under the following captions:
• Ordering Information
• Voltage Regulator
• DC Characteristics
• AC Characteristics
• Timing Considerations
• Clock Considerations
• HALT/RESET Logic
December 17, 1986 6-17

ABSOLUTE MAXIMUM RATINGS Storage Temperature (TsTG) rating are from -65°C to +150 o G
SYMBOL PIN DESCRIPTION RATING UNIT
Vee Vee Supply voltage +7.0 V

X1, X2 Crystal input voltage 2.0 V
All other pins logic input voltage 5.5 V
DC ELECTRICAL CHARACTERISTICS (Commercial Part) 4.75V';;; Vee';;; 5.25V, OOG';;; TA';;; 70 G 0
LIMITS
SYMBOL PARAMETER TEST CONDITIONS UNIT COMMENTS
Min Typ Max
Vee Supply voltage 4.75 5 5.25 V

0.9 2 X1 and X2
V ,H High-level input voltage V
2 5.5 All other pins
0.5 X1 and X2
V,L Low-level input voltage V
0.8 All other pins
VOH High-level output voltage Vee =min; IOH = -3mA 2.4 V

Vee = min; 10L = 6mA 0.55 Ao through A12
VOL Low-level output voltage V
Vee = min; 10L = 16mA 0.55 All other outputs
3.1 TA = OOG
VeR Regulator voltage Vee = 5V V
2.9 TA = 70 0 G
Grystal inputs X1 and X2
Vie Input clamp voltage Vee = min; liN =-10mA -1.5 V do not have internal
clamp diodes
V,H = 0.9V 4 mA X1 and X2
I'H High-level input current Vec = max
V,H = 4.5V 50 p.A All other pins
-3 X1 and X2
-0.2 IVO-IV7
I,L Low-level input current Vee = max; V,L = O.4V mA
-1.6 10-115
-0.4 HALT and RESET
Vee = max; (Note: At any
time, no more than
los Short circuit output current -30 -140 mA All output pins
one output should be
connected to ground.)
180 TA = 70 0 G
Ice Supply current Vce= max mA
195 TA = OOG
Max available base drive
IREG Regulator control Vee = 5.0V -10 -25 mA
for series-pass transistor
200 TA = 70 0 G
leR Regulator current Vce= max mA
230 TA = OOG
NOTES:
1. Operating temperature ranges are guaranteed after thermal equilibrium has been reached.
2. All voltages measured with respect to ground terminal.
December 17, 1986 6-18

AC ELECTRICAL CHARACTERISTICS (Commercial Part) Conditions: 4.75V~Vcc~5.25V; O°C~TA~70°C

Loading: (See test circuits)
LIMITS (INSTRUCTION LIMITS (INSTRUCTION

SYMBOL PARAMETER (NOTE 1) CYCLE TIME = 200ns) CYCLE TIME> 200ns) UNITS COMMENTS
Min Typ Max Min Typ Max
tpc Processor cycle time 200 200 ns
tcp X1 clock period 100 100 ns
tCH X1 clock high time 50 50 ns
tCl X1 clock low time 50 50 ns
tMCl MCLK low delay 15 40 15 40 ns
tw MCLK pulse width 35 55 T 40 -15 T 40 +5 ns Note 2
too Input data to output data 70 105 70 105 ns
MCLK falling edge to HALT
tMHS 30 TlQ - 20 ns Note 2
falling edge
HALT hold time
tMHH (MCLK falling edge)
65 TlQ + 15 ns Note 2
tACC Program storage access time 60 ns

I/O ~ output en~ble time
t,O 30 ns
(LR/RB to val ide IV data input)
MCLK falling edge to address TlQ +
tMAS 140 ns Notes 2, 3, & 4
stable T 20+ 40
t'A Instruction to address 140 T20 + 90 ns Notes 2, 3 & 5
t,VA Input data to address 85 85 ns Notes 3 & 6
MCLK falling edge to instruction
tMIS 25 TlQ - 25 ns Notes 2 & 7
stable
Instruction hold time
tMIH (MCLK falling edge) 55 T,o+5 ns Notes 2 & 8
MCLK falling edge to SC/WC T,o+ TlQ +

tMWH 105 125 ns Note 2
rising edge T 20 + 5 T 20+ 25
MCLK falling edge to SC/WC
tMWl 2 15 2 15 ns
falling edge
MCLK falling edge to LB/RB
tMIBS 5 25 5 25 ns
(Input phase)
Instruction to LB/RB
tllBS 25 25 ns
(Input phase)
MCLK falling edge to LB/RB
115 145 TlQ + TlQ + ns Note 2
tMOBS (Output phase) T20 + 15 T20 + 45
MCLK falling edge to input data TlQ +
tMIOS 55 ns Note 2
stable T 20 - 45
Input data hold time TlQ +
tMIDH
(MCLK falling edge) 115 ns Note 2
T 20+15
Output data hold time
tMOOH 11 11 ns
(MCLK falling edge)
Output data stable TlQ + TlQ +
tMooS 123 150 ns Note 2
(MCLK falling edge) T 20 + 23 T 20 + 50
Output data stable
toOSM 10 t30- 4O ns Note 2
(MCLK rising edge)
NOTES:
1. X1 and X2 inputs are driven by an external pulse generator with an amplitude of 1.5 volts; all timing parameters are measured at this voltage level.
2. Respectively, T 1Q, T 20, T30. and T 4Q represent time intervals for the first, second, third, and fourth quarter cycles.
3. Capacitive loading for the address bus is 150 picofarads.
4. TMAS is obtained by forcing a valid instruction and an 1/0 bus input to occur earlier than the specified minimum set up time.
5. TIA is obtained by forcing a valid instruction input to occur earlier than the minimum set up time.
6. TlvA is obtained by forcing a valid 1/0 bus input to meet the minimum set up time.
7. TMIS represents the setup time required by internal latches of the 8X305. In system applications, the instruction input may have to be valid before the worst·case
set up time in order for the system to respond with a valid 1/0 bus input that meets the 1/0 bus input set up time (T lDs and T MIDS).
8. TMIH represents the hold time required by internal latches of the 8X305. To generate proper IS/RB signals, the instruction must be held valid until the address
bus changes.
December 17, 1986 6-19

Signetics Microprocessor Procucts Product Specification
AC TEST CIRCUITS
5V 5V
787H 237n
OUTPUT OUTPUT
UNDER TEST UNDER TEST
374U 150pF 169!l 300pF
NOTE:
Load capacitance includes Test Jig and Probe Capacitance
TIMING CONSIDERATIONS all parameters that are cycle-time dependent Condition 1 - Instruction or MCLK to LB/RB
is likewise increased. In some cases, these (input phase) plus I/O port ac-
(Commercial Part)
delays have a significant impact on timing cess time (TIO) < fV data set-
As shown in the AC CHARACTERISTICS
relationships and other areas of systems up time (Figure 5a).
table for the commercial part, the minimum
design; subsequent paragraphs describe
instruction cycle time is 200ns; whereas, the Condition 2 - Program storage access time
these timing parameters and reliable methods
maximum is determined by the on-chip oscil- (TACC) plus instruction to LS/
lator frequency and can be any value the user of calculation.
RS (input phase) plus I/O port
chooses. With an instruction cycle time of Timing parameters for the 8X305 are normal- access time (TIO) plus fV data
200ns, the part can be characterized in terms ly measured with reference to MCLK. (input phase) to address < in-
of absolute values; these are shown in the struction cycle time (Figure
System determinants for the instruction cycle
first" LIMITS" column of the table. When the 5b).
instruction cycle time is greater than 200ns, time are:
• Propagation delays within the 8X305 Condition 3 - Program storage access time
certain parameters are cycle-time dependent;
• Access time of Program Storage plus instruction to address
thus, these parameters are specified in terms
of the four quarter cycles (T 10, T2Q, T3Q, and • Enable time of the I/O port
< instruction cycle time (Fig-
ure 5c).
T4Q) that make up one instruction cycle-
Normally, the instruction cycle time is con-
see 8X305 TIMING DIAGRAM. As the time
strained by one or more of the following
interval for each instruction cycle increases
conditions:
(becomes greater than 200ns), the delay for
I I I I , ~
, ," , I"'II
H !: H
~~ ~
1
,----v. 1 : ~ MCLK I I I I I 1
~'
MCLK ----Jj : '
MClK-.i
SC,WC,lB -a:c' ~
I \
II
~
It
AO-A12~! I
i ! ~i
f-T-CD---I.j I I I I 10-115
l~-::'
I I I I I I I
orRB I~@:~ i 1 :
151
: I~
\ "~"
I I: I I I I I
'E='" ~
10-1 I II I AO-A12 II I I I::
::~:
I I
IVO-1V7 I
I I
I
I
I
I
I
r i : ~ :INSTRUCTlON: I I
l::
I I
I 11 I I I LB,RBI : ~ I I I I : ITO ADDRESS I :
:-0-fi :I lI :I : : \ - i (Ii ~L-..j ~ I I I I I ------+--r I
1VO- 1V7 r",~

I I I I PROGRAM I
I I
I I I
,
I STORAGE
" I ACCESS
NOTES: NOTES:
CD MCLK to IS/AB (input phase) or instruction to CD Program s~a~ access time.
[BlAB (input phase). ® MCLK to LB/RS (input phase) or instruction to
® I/O port access (TIO). 03/R8 (input phase).
® TV data setup time (referenced to MCLK). ® !fO port access (TIO).
@ iV data (input phase to address.)
a_ Condition # 1 b_ Condition # 2 c. Condition #3
Figure 5_ Constraints of 8X305 Instruction Cycle Time
December 17, 1986 6-20

Signetics Microprocesscr Products Product Specification
8X305 TIMING DIAGRAM
I--C---- PC ---- .. 1
r=ICl~_ICP~
XI ______________,
MClK -----'I I~----------------------~I I~____________

I• IMAS~ I--IW--j
ADDRESS ;'
<Aa-Au) - - - - - - - - - - - - - - - - - - - - - - - - , . - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
: 1-1........------------------- 1, . . . : IACC 1 .. I
I. tVA - I
lNS(~:~I~:;ON ?~===========,;17"" I I ~'~~----------
SCIWC
1,- TM'S _I. II
II---------<.~
IMI ..
,
:
I
-..J IMWL
hg'~~ .~" J! \
(j/iil! ==--=---=---=---------,-,-'--".~~E I~ t: I X
Pm-1V'1 ~ OUTPUT
~S I MOBS
INPUT
J : -I
OUTPUT
I MODH f--
H.UT _ _ _ _ _ _ _ _ ~IM~H~S_~~·_,I rl::M:,:DH::::~,D~D~::l::::::~---1i-----------------------

t :
~
~
1-_1--
IMHH_I
_________________ 1MOOS -------------001
i~ t OOSIl
• INDtCATES CHANGING DATA
• INDtCATES 3·STATE :. INPUT PHASE • : .. OUTPUT PHASE - , '

I I I I
~ IMtruction , . .
I open
-.J
I
t..-
I
IMtruction 1ICtdr• • ~MCLK ....
cMIIgM I
-----1
I
: : I SC=-1~torI/O :
... sc ==wc ="0" .. :_ eddreM.wc=~,-fot' .. I
:
Iii
:
I
Ili. • _t~lnputo.t.
i
..!:
I
iii
I/OdMII
[I,JlI ... ,~autput . .
i
------i
I
I
:... I/O drtweN; ttw'....tMe - - - -......o-l~ 1/0drfv.,. acthl~ If output UIII 01 ~
I I I eddr... to 1/0 BUS;~"""" ottwwi.. I
:_ tlO'~;w.,.open _: :: :
I I I ..... --~I/Obul . . . ~
: i : ~ :
..
: .........- - - - - - - - - - -....
I I
: - - - - - - - - ONE ~YCLE
I
-------+:-------...,.. :
, I
NOTE:
For an instruction cycle time greater than 200n5, the 1/0 bus can be stable sometime within the third quarter (T3Q) cycle.
December 17, 1986 6-21

From condition # 1 and with an instruction valid at the falling edge of MCLK. This rela- noise. For various capacitor (Cx) values, the
cycle time of 200ns, the 1/0 port access time tionship can be derived by the following cycle time can be approximated as:
(TIO) can be calculated as follows: equation:
APPROXIMATE CYCLE
TMIBS + TIO ,,;;; TMIDS 200ns - TMAS - TACC Cx (in pF)
TIME
transposing, TIO";;; TMIDS = TMIBS = 200ns - 140ns - 60ns
substituting, TIO";;; 55ns - 25ns = Ons 100 300ns
result, TIO";;; 30ns 200 500ns
It is important to note that, during the input 500 1.1I'S
Using 30ns for TIO, the constraint imposed by phase, the beginning of a valid LB/RB signal 1000 2.01's
condition # 1 can also be used to calculate is determined by either the instruction to LBI
the minimum cycle time: RB delay (TIIBS) or the delay from the falling Crystal Timing. When a crystal is used, the
edge of MCLK to LB/RB (TMIBS). Assuming on-chip oscillator operates at the resonant
TMIBS + TIO";;; TMIDS
the instruction is valid at the falling edge of frequency (fo) of the crystal. The series-
thus, 25ns + 30ns ,,;;; T 10 + T2Q - 45 MCLK and adding the instruction-to-LB/RB
25ns + 30ns";;; 112 cycle - 45 resonant quartz crystal connects to the
delay (TIIBS = 25ns), the LB/RB signal will 8X305 via pins 10 (X1) and 11 (X2). The lead
therefore, the worst-case instruction cycle be valid 25ns after the falling edge of MCLK. lengths of the crystal should be approximate-
time is 200ns. With subject parameters refer- With a fast program storage memory and with ly equal and as short as possible. Also, the
enced to X1, the same calculations are valid: a valid instruction before the falling edge of timing circuits should not be in close proximity
MCLK - the LB/RB signal will, due to the to external sources of noise. The crystal
TIBS+ TIO + TlDS';; 1/2 cycle TMIBS delay, still be valid 25ns after the should be hermetically sealed (HC type can)
thus, 45ns + 30ns + 25ns';; 112 cycle falling edge of MCLK. Using a worst-case and have the following electrical characteris-
therefore, the worst-case instruction cycle instruction cycle time of 200ns, the user tics:
time is again 200ns. From condition # 2 and cannot gain a speed advantage by selecting a Type - Fundamental mode, series reso-
with an instruction cycle time of 200ns, the memory with faster access time. Under the nant
program storage access time can be calculat- same conditions, a speed advantage cannot Impedance at Fundamental- 35n max.
ed: be obtained by using an 1/0 port with fast Impedance at Harmonics and Spurs-
access time (TIO) because the address bus 50n min.
TACC + TIIBS + TIO + TIVA will be stable 55ns (TAS) after the beginning
,,;;; 200ns of the third quarter cycle - no matter how The resonant frequency (fo) of the crystal is
transposing, TACC';; 200ns - TIIBS - TIO early the 1\7 data input is valid. related to the desired cycle time (T) by the
-TIVA equation: fo = 2/T; thus, for a cycle time of
substituting, TACC';; 200ns - 25ns - 30ns 200ns, fo = 10MHz.
-85ns CLOCK CONSIDERATIONS HALT Logic
thus, TACC';; 60ns The on-chip oscillator and timing-generation The HALT signal is sampled via internal chip
hence, for instruction cycle time of 200ns, a circuits of the 8X305 can be controlled by any logic at the end of the first int<;lrnal quarter of
program storage access time of 60ns is one of the following methods: each instruction cycle. If, when sampled, the
implied. The constraint imposed by condition Capacitor - if timing is not critical HALT signal is active-low, a halt is immediate-
# 3 can be used to verify the maximum Crystal - if precise timing is required ly executed and the current instruction cycle
program storage access time: External Drive - if application requires that is terminated. However, the halt cycle does
the 8X305 be driven from not inhibit MCLK nor does it affect any
TIA + TACC .;; Instruction Cycle internal registers of the 8X305. As long as the
thus, TACC';; 200ns - 140ns a system clock
HALT line is active-low, the SC and WC lines
and, TACC";;; 60ns Capacitor Timing_ A non-polarized ceramic are low (inactive), the Left Bank (LB)/Right
confirming that a program storage access or mica capaCitor with a working voltage Bank (RB) signals are high (inactive), and the
time of 60ns is satisfactory. equal to or greater than 25V is recom- 1\7 bus remains in the 3-State mode of opera-
mended. The lead lengths of capacitor should tion. Normal operation resumes at the next
For an instruction cycle time of 200ns and a be approximately the same and as short as cycle in which HALT is high when sampled
program storage access time of 60ns (Condi- possible; also, the timing circuits should not (see HALT TIMING DIAGRAM.)
tion # 2/Figure 5b), the instruction should be be in close proximity to external sources of
December 17, 1986 6-22

HALT TIMING DIAGRAM
:~~--- HALT CYCLE ----I

I
x,
------I i~THH
1 1
THS----...! I.-!
Note 1 Note 2
HALT------------------~~\~,~~~,~,~,~,~,~,;,~,~,,~,~,~,~,~,I : ~~-r-r-r--r-r-r~r-r--r-r-r--r-r-,~-------------------------
'\ '\ '\ \ '\ '\ '\ \ '\ '\ \
\ \ '\ '\ '\ '\ I / / / / / / / / / / / / / It.
\\\"\\\\\\\'\\\\'\ /l /////1/111/////
'-'-'-'-'-'-'-'-'-'-'-'-'-'-"-1'-'--...1 -y'......I ../.J...J-/../...J.../J"/-/..../-/-I
!
TMHS -------.1 1-4------

TMHH----..: !~
ou%~~~_~~~1i<~~:~~~~__
1
SC & we ----------___
\ / :\ /
1
X X :1 \( X
MeLK
NOTES:
1. The HALT signal can switch from High to Low at any time during this interval.
2. The RArf signal can switch from Low to High at any time during this interval.
TIMING DESCRIPTIONS:
T HS - setup time from R'ACf to X1 (independent of instruction cycle time)
THH - hold time from X1 to HALT (independent of instruction cycle time)
T MHS - setup time from MCLK to HALT (dependent upon instruction cycle time)
TMHH - hold time from MCLK to HALT (dependent upon instruction cycle time)
December 17, 1986 6-23

QUARTE:6~~~:~---1-------~------~------~~~----~------~-------
MeLK
ADDRESS---------~----------~~-~-~.~~~r----------------
AO-A12-----------t----------~---t_-I~~~~~~~~------------
sc'wc-----------1~~~
[Bd," __________-.:..,-~'_____i-_+_--"::::O___- J ' '-/_-+_________-"'-___
NOTES
~ DENOTES CHANGING DATA
m.m DENOTES HI-Z
Figure 7. Timing Relationships of 8X305 1/0 Signals
December 17. 1986 6-24

Using an External Clock. The 8X305 can be

synchronized with an external clock by simply e-
connecting appropriate drive circuits to the + Xl=~ I
X1/X2 inputs. Figure 8 shows how the on-

SOil
chip oscillator can be driven from the comple-
8X305
h
mentary outputs of a pulse generator. In PULSE
GENERATOR MICROCONTROLLER
applications where the Microcontroller must
be driven from a master clock, the X1/X2 soil
lines can be interfaced to TTL logic as shown
in Figure 9.
- X2=~
RESET Logic
RESET (pin 43) can be driven from a high PULSE GENERATOR CHARACTERISTICS:
(inactive) state to a low (active) state at any ZOUT = 50D
RISETIME ~ 10ns
time with respect to the system clock, that is, VOUT = 0 to 1.5V
the reset function is asynchronous. To ensure <
Skew 10ns
proper operation, RESET must be held low Figure 8. Clocking With a Pulse Generator
(active) for one full instruction time. When the
line is driven from a high state to an active-
• The input! output (iV) bus goes 3-State During the time RESET is active-low, MCLK is
low state, several events occur - the precise
and remains in that condition as long inhibited. Moreover, if the RESET line is
instant of occurrence is basically a function of
as the RESET line is low. driven low during the last two quarter cycles,
the propagation delay for that particular
• The Select Command and Write MCLK may be shortened for that particular
event. As shown in the RESET TIMING
Command signals are driven low and machine cycle. When RESET line is driven
DIAGRAM. these events are:
remain low as long as the RESET line high (inactive) - one quarter to one full in-
• The Program Counter and Address
is low. struction cycle later, MCLK appears just be-
Register are set to address zero and
fore normal operation is resumed. The RE-
remain in that state as long as the • The Left Bank/Right Bank (LB/RB)
SET /MCLK relationship is clearly shown by
RESET line is low. Other than PC and signals are forced high asynchronously
"B" in the timing diagram. As long as the
AR, RESET does not affect other for the period in which the RESET line
RESET line is active-low, the HALT signal
internal registers. is low.
(described next) is not sampled by internal
logic of the 8X305.
December 17, 1986 6-25

Microcontroller 8X30S
1. Using a 74LS136 Quad Execlusive-OR gate (open collector). 2. Using a 74LS266 Quad Exclusive-NOR gate (open collector)
+5V +5V 8X305

+5V BX305
lk
lk
) - -....- .. X2 SYSClK
SYSCLK )O--....--IX2
lk
lk
)--4----1 Xl
)o---+--i Xl
3. Using a 74F38* Quad NAND gate (open collector). 4. Using a 74LS286 Quad Exclusive-OR gate.
+5V 8X305
8X305
+5V
lk
SYSCLK 500
X2
X2
SYSCLK
lk
500
Xl
Xl
-=
TTL DRIVER CHARACTERISTICS,
Fall Time.o;;;;; 1Dns
Skew Between Complementary Outputs.o;;;;; 1Dns
NOTES,
1. All circuits, as drawn, preserve the phase relationship of SYSCLK to X1.
2. The resistor values of 1k ohms for open-conector pull-ups and 500 ohms for active pull-up series resistors are calculated to be optimum for all opening conditions and silicon
varations.
3. The BX305 clock may be driven by circuits other than those shown here. The circuits shown however, have been tested under conditions in excess of those that will be found in a
normal system. Exclusive-OR/NOR type gates were selected to minimize the skew between the X1 and X2 inputs.
4. 74LS38 and 74S38 gates were tested in addition to the 74F38 chip. These were found to be the least robust configurations of all those tested, although they did work over normal
operating conditions abd beyond. When failure occured it was due to excessive skew between X1 and X2 caused by the inverting gate in the X1 leg.
Figure 9. Clocking With TTL
December 17. 1986 6-26

RESET TIMING DIAGRAM
,
RESUME NORMAL OPERATION
"_
Note 1 -,-rrryrr
11//1/"
//1/11
Note 2
1 ,'
~----------------------~r------------~/~~~~J~~I
L
W.BUS
OUTPUTS ----.
------./
--~----~~~~\------------~I
SC&WC
"<'------)(
~- ----------------------------------------------~ n ~-----------
NOTES:
1. A High to Low transition of the RESET signal will force the Address Bus to an all-zero configuration.
2. The RESET signal can switch from Low to High at any point within this time interval and, in all cases, MCLK will occur at least one-quarter cycle time later as shown.
December 17, 1986 6-27

Signetics 8X401
Microcontroller

The Signetics 8X401 Microcontroller is a • Fetches and executes all
very high-speed bipolar microprocessor instructions in a minimum of
implemented with internal Eel technolo- 150ns
gy. The 8X401 Microcontroller combines • Bit manipulation-oriented
speed, flexibility, and a bit-oriented in- instruction set
struction set to accommodate many so- • Separate buses for instruction,
phisticated applications. It excels in sys- instruction address and I/O
tems that require high-speed bit or byte
• Sixteen 8-bit registers
manipulations, such as high-speed con-
trollers and data communications. • On-chip interrupt control
• TTL compatible I/O
The 8X401 can fetch, execute, and gen-
erate the next instruction address for a • Single + 5V supply
20-bit instructio(1 in a minimum of 150ns. • 0.9-inch 64-pin DIP, 68-pin plastic
Within one instruction cycle, the 8X401 leaded chip carrier
can be programmed to input, right-rotate • Two user-definable status flags
and mask single or multiple bit subfields, • Single TTL clock input
perform an AlU operation, left-rotate, • Three independent I/O banks
merge the subfield into the destination,
• On-board control sequencer
and output.
• On-chip subroutine capabilities
To interface with program memory, the
• Fixed instruction set - 32
8X401 uses a 13-bit address bus and a Instructions
20-bit instruction bus. An 8-bit bidirec-
tional data/address bus, and an I/O • Complete development support
control and timing bus is used to access
external peripheral devices.
DESCRIPTION ORDER CODE
64-pin Ceramic DIP - 900 Mil Wide N8X4011
64-pln Plastic DIP - 900 Mil Wide N8X401N
December 17, 1966 6-28

BLOCK DIAGRAM OF THE 8X401
.:':.,- --
AODRESS
--~=;-- -- - -- - -- -- - - -- ---,
COUNTER LEGEND I
I 13
(PC)
I
0
I
ADDRESS FLOW
I I
I
I
I ADDRESS
REGISTER (AR) ·7
PROGRAM
[SJ
I§lI
INSTRUCTION FLOW
DATA fLOW
I
I
I COUNTER I
STACK
~ ADDRESS BUS
I
I
I ADDRESS
I EE
1
DATA ADDRESS BUS
I SOURCE
MUX
I
I ~ INSTRUCTION BUS I
I R17
I
I SF
R11 I
I I
I IR
NZ
,I PS
, I I I I
cv
SI
I
REGISTERS
I
GENERAL PURPOSE RO~RB,RF .d.. ~j!il3~1llll!llllml!!!l
I 1'!'!'''~''f'"''T:,F'1I---------~~',4.~
r- ADDRESS REGS RC-RE ¢-- REGISTER
MERGE
I ~H I~ii
I H 11 CARRY Rl0
STATUS R11 1-....,_-' ..
~, 1:"
I. .
I
, ..L..J"--.... LENGTH/MASK
VECTOR ""BIT",
EZ:
LENGTH/MtSK VECTOR
:":TITITII",,,,,,~;;,,,,,§2':::""lillTII,;;":,c[JJIT:"''''':ITm'':;'':~''::::--~~
I XEC MUX ~ii:
~
LENGTH/MASK
VECTOR
I ALU
11
~~ RIGHT
I SOURCE
MUX
ROTATE
I " i', '-----'

I " I~~-~~ RB
,~~ L-.-..y/
~ ~
ALU _ LEFT
ROTATEF
b
,
I'R12 -
IRa
~ '\ SECOND SEE NOTE
~~~s2~~'~~~~~S:~~If:IR,,~7_=IR=~$>L-_0_P~;~~~~N_C~ --~
INSTRUCTION'
, CARRY
NZ Rl0
~~$~~ESl~~' ~
BUS R17
19-10
I
~
INSTRUCTION
I I 20 .. REGISTER (IR) LENGTH/MASK VECTOR
, 1/0 INTERfACE
I
i INPUT 110 •
I LATCH
~"'~5il~~
, "
"\~ IR19-IRO
MERGE
I
INT-4--------I
Niii
r--;:::=====;-i--;:-
I R1B-R1 F
I---
F)INTERNAL
CONTROL
LENGTH/MASK
VECTOR ~
ff I" CABUS
SCR~--------I LEFT ROTATE

RE~-+I-------------I
TIMING & CONTROL
~-T--------------~
CP-L-------------J
I Rll-R16
110 ENABlE
December 17, 1986 6-29

PIN DESCRIPTION
PIN NO. IDENTIFIER FUNCTION
1, 17, 47 GND Ground.
Program Address Lines: These active-high outputs permit direct addressing of up to 8192
2-14 A12-AO
locations of program storage; AO is LSB.
Non-Maskable Interrupt: The falling edge of this active-low input pin generates a non-
15 NMI
maskable interrupt.
Interrupt: This active-low input pin is tested during the fourth quarter of each instruction cycle.
16 INT If an interrupt is indicated and if interrupts are enabled, the address of the next instruction that
was to be executed is stored onto the program counter stack before the interrupt is serviced.
Instruction Lines: These active-high input lines receive 20-bit instructions from program
18-37 119-10
storage; 10 is LSB.
Bank A: When low, devices connected to bank A are accessed. (Note: Typically, the A signal
38 A is tied to the ME input pin of 1/0 peripherals.)
Bank B: When low, devices connected to bank B are accessed. (Note: Typically, the B signal
39 B is tied to the ME input pin of 1/0 peripherals.)
Bank C: When low, devices connected to bank C are accessed. (Note: Typically, the C signal
40 C is tied to the ME input pin of 1/0 peripherals.)
41 SC Select Control: When high, an address is being output on pins DA7 through DAO.
42 WC Write Control: When high, data is being output on pins DA7 through DAO.
43-46 Data Address Bus: These active-low, bidirectional, three-state lines are used for 1/0; DAO is
DA7-DAO
48-51 LSB.
52,64 Vcc + 5V power supply.
Master Clock: This active-high output signal is used to strobe data into data peripherals for
53 MCLK clocking 110 devices andlor synchronization of external logic. MCLK is active-high in the fourth
quarter cycle.
Read/Write Clock: This active-high output signal is used for synchronization of external logic
54 RWC
and is active-high during the third and fourth quarter cycles.
55 RESET Reset: The RESET input pin is used to initialize the 8X401.
Halt: The HALT input is sampled during the first quarter cycle of each instruction cycle. When
56 HALT
the HALT input is low, the instruction cycle is not executed.
Slow Clock Request: This active-low control input is sampled during the first quarter cycle of
each instruction. When SCR is asserted, it will cause the current instruction to be executed at
57 SCR half of the normal clock rate. This control input is necessary to accommodate 1/0 devices that
cannot operate at the 8X401's full speed, without having to continuously run ihe 8X401 at half
speed.
58 CP Clock Pulse: Each 8X401 quarter cycle will correspond to one full cycle of the clock pulse.
Status Input: The value of the SI pin during the fourth quarter cycle is transferred to SI bit in
59 SI
the status register.
60 PS Programmable Status: The programmable status pin is controlled entirely by the user program.
61 NZ Non-Zero: The NZ bit of the status register is reflected on this pin.
Interrupt Receivable: The IR pin indicates whether an interrupt applied at any point in time
62 IR will be serviced. Interrupts are receivable when the interrupt mask (status register, bit 0) is
clear and the stack is not full (1M = 0 and SF = 0).
63 CY Carry: Carry bit from R10 is output on this pin.
December 17, 1986 6-30

SMALL SYSTEM pleted operation. Any TTL-compatible memo- 80th data and I/O address information are
I
CONFIGURATION
The system hookup shown on the next page,
ry can be used for program storage, provided
the worst-case access time is compatible with
multiplexed on the DA bus. The SC (Select
Command) and WC (Write Command) signals r
although of the simplest form, provides a the instruction cycle time used for the appli- distinguish between data and I/O address I
fundamental example of the 8X401 Microcon- cation. See timing section for appropriate information as shown in the table below.
troller and compatible peripheral relation- calculations. Although the table shows bank A only, the
ships. As shown, the 8X401 can directly same conditions apply to banks 8 and C.
address up to 8K locations of program stor-
age. 110 INTERFACE AND CONTROL BANK
The Data Address (DA) bus is an 8-bit bidirec- SC WC FUNCTION
A
Each of the three bank pins (A, B, or C) are tional I/O bus which provides a communica-
capable of uniquely addressing 256 input! tion link between the 8X401 and the three High Low Low DA bus is three-
output locations via the Data Address bus banks of the I/O devices. The A (A bank), B state and not
(DA7-DAO). (8 bank), and C (C bank) control signals looking for input
identify which bank is enabled. When all three data.
The addressable locations for each bank can
be used in a variety of ways. The hookup banks go high (inactive), neither bank is Low Low Low The DA bus is
shown below is just one method of implemen- enabled and the DA bus is inactive (three- reading input data.
tation. state). A functional analysis of the three bank
signals is shown below: Low Low High Data is being
When a particular bank signal is asserted, output.
that bank is enabled and anyone of 256 A B C FUNCTION Low High Low Address is being
locations on that bank can be accessed for output.
input! output operations. Low Low Low This state is not
generated by the X High High This condition is
8X401. never generated.
PROGRAM STORAGE Low High High Enable A bank
INTERFACE devices.
As shown in the 8X401 small system hookup,
program memory is connected to output ad- High Low High Enable 8 bank
dress lines A12 through AO (AO = LS8) and devices.
input instruction lines 119 through 10 High High Low Enable C bank
(10 = LS8). An address output on AI2-AO devices.
identifies one 20-bit instruction word in pro-
gram memory. The program memory outputs High High High Disable all devices;
an instruction word on 119 -10 which defines DA bus is three-
the microcontroller operation which is to fol- state
low. One instruction word equals one com-
December 17, 1986 6-31

SUPPLEMENTARY TIMING SIGNAL
_B
258 ADDIIEIlSAa.E
LOCATlONII
m INSTRUCTION ADDRESS
~ INSTRUC110N IMTA
133 DATA. - . AND CONTROL
8X401 Small System Hookup
December 17. 1986 6-32

DATA PROCESSING tion to being general purpose. A summary of into the AUX, the left-rotate and merge
The data processing section of the BX401 the registers is listed below: functions are inhibited when specifying
consists of a number of logical subsections. • RO (Auxiliary Register) - Register 0 is the AUX as a destination address. This
In order of processing, the data sees the right also used as the implied second allows subfields from any internal
rotator, the ALU, the left rotator, and the operand for two operand instructions register or I/O bank to be transferred
merge circuits. Data sources and destinations (ADD, ADD with CARRY, XOR, AND). to the AUX with the subfield LSB right-
can be various on-chip registers, the bidirec- The primary operand is specified in the justified and unspecified bits set to zero.
tional DA bus, or immediate subfields. The source field of the instruction word and • R1 through RA - These 10 addresses
data processing paths are shown below. the AUX register is the implied second specify general-purpose, on-chip storage
operand. Prior to performing arithmetic registers.
or logical operations (other than the
• RB - Register B is also used as the
DATA REGISTERS IMMEDIATE operation), it is assumed implied source for the XEC instruction.
that RO contains the appropriate data.
General-Purpose Storage In order to reduce the possibility of • RF - Register F is also used as the
There are 13 source/destination general-pur- implied destination for the XOR
erroneous results and to minimize the
pose registers available on the BX401. Three IMMEDIATE and AND IMMEDIATE
number of instructions required to
of these registers, specifically Registers 0, B, instruction classes.
transfer a right-justified second operand
and F, have other special functions in addi-
IR NZ PS cY SI
I Itt 1
GENERAL PURPOSE fIOoR8, RF A
I!!Pi iI!W ADDRESS REGS RC-RE
REGISTER
MERGE
CARRY R10 ~
t-~S~TA=IVS~~R~17~----------------~
ALU
SOURCE
MUX
I/O INTERFACE
December 17, 19B6 6-33

Enabled 1/0 Addresses RY. NZ can also be written to directly when pressed. This allows byte rotate operations to
These three registers (RC RD, and RE) al- specified in the destination field. This opera- be performed. The left-rotate is also sup-
ways contain the address of the most recent- tion will negate and take priority over the pressed when the destination is register O.
ly enabled 110 device for each of the three 1/ normal setting by the ALU output. NZ is not This is the AUX register and is used as the
o banks. When register C, 0, or E is the affected after an XMIT instruction, or after a implied second operand in· certain instruc-
specified destination address, the destination write to R17. tions.
data is sent to both the on-chip register and Bit 2: (PS) - This is the Programmable Sta- It should also be noted that subfields are
the corresponding bank on the DA bus. The tus bit. The contents are reflected on the PS defined at the ends of a register; for example,
relationship between the register addresses output pin. This status is controlled entirely by bit positions 1, 0, 7, and 6 constitute a
and I/O banks is shown below: the user program. contiguous 4-bit subfield.
REGISTER BANK Bits 3 and 4: (UFO, UF1) - These two bits Data Field - The data field holds data that
represent user flags and have no assigned can be processed directly from the instruction
C A
functions. They can be used as l-bit internal word.
o B flags and are entirely under control of the
E C
user program.
When these registers are specified as a
Bit 5: (51) - This bit reflects the state of the
LEFT-ROTATE OVERRIDE
destination address, the L field must be set to BLOCK
status input pin. This read-only bit is updated
o (full 8-bit operation). Also, note that regis- during the 4th quarter cycle. Register addresses 18-1 F are destination
ters C, 0, and E may not be used with the only and are used to independently control
XMIT 5 or ADD IMMEDIATE 5 instructions. Bits 6 and 7: (SE, SF) - These read-only bits left rotation of data prior to storage in the
indicate Stack Empty and Stack Full, respec- destination. Specifying 18-1 F as a destination
Carry tively. The bits are updated during the 3rd
Register 10 contains the Carry bit. Bit position causes the data to be returned to the source
quarter cycle within the instruction thaI. alters address.
o (LSB) is the Carry bit, and positions one
the stack status.
through seven are always zero. The Carry bit In order to move a processed subfield within
is updated each time an ADD, ADD IMMEDI- the same register but in different bit positions
ATE, or ADD WITH CARRY instruction is (the LSB of the contiguous subfield can vary),
performed. When specifying address 10 as a
INSTRUCTION WORD (See
it is necessary to independently specify the
destination, only bit 0 (the Carry bit) will be Table 3) LSB for both the source and destination. The
written to. Data written to the Carry bit will be Operations Code Field - The 4-bit opcode order of operation is as follows:
the LSB of the right-rotated data after any specifies one of 16 classes of instructions. • Register or I/O source data is right-
specified operation. Some instructions require two additional su- rotated as specified by the "R" field.
When the Carry register is the explicit desti- bopcode fields, X and XS. Variations and Along with the "L" field, the subfield
nation of any ADD instruction, it will contain interpretations are displayed in Table 2. data is defined.
the carry resulting from the add operation Source (5) and Destination (D) Fields- • Subfield data is processed via the ALU.
rather than the LSB of the sum. Carry can The 5-bit "S" and "D" fields specify the • Data is left-rotated 0 - 7 bits, depending
also be affected via the Return and Set Carry source and destination, respectively, for the on the corresponding register addresses
or Return and Clear Carry instructions. operation that is defined by the opcode. The 18-1 F as specified in the destination
"S"· and/or "D" fields specify an internal field rather than using the "R" field.
Status Register
This address specifies the current condition 8X401 register or a variable length field from • After left-rotation the specified subfield
of the 8X401 system. The status register may an 110 device. Hexadecimal values and is merged into those bits of the original
be either a source or destination; however, source/destination field assignments for all source data. The unspecified bits of the
certain bits in the status register are read- internal registers are shown in Table 1. original source data remain unchanged.
only. Four status outputs are available on When RC-RE (banks A, B, or C, respectively) • Result is stored in the register address
8X401 pins. They are NZ (Not Equal to Zero), are specified as the destination, the data is specified by the source field.
PS (Programmable Status), IR (Interrupts Re- output onto the DA bus using the specified Note that the left-rotate is always inhibited if
ceivable), and Carry (Rl0, bit 0). The IR pin bank. The data is also stored in the specified the "L" field is zero. Also, addresses 18-1 F
goes high when the interrupt mask is clear register and may be later accessed as source may not be used in the destination field for
and the stack is not full. The IR output is data. the XMIT or ADD IMMEDIATE instructions.
updated during the 4th quarter cycle. The
Rotate (R) and Length (L) Fields - The R The destination addresses and correspond-
following descriptions define the bits within
field is used in conjunction with the L field to ing left-rotate values are shown in Table 2.
the status register.
define the desired data within a register or 1/
Bit 0: (1M) - This bit represents the Interrupt o device. The source data is right-rotated
Mask control. When 1M is set, the interrupt is prior to ALU operations, such that the bit DA BUS CONTROL BLOCK
inhibited. This bit is set automatically by a specified by the R field is right-justified. The L Register addresses 11 - 16 are used by the
response from a standard or non-niaskable field specifies the number of bits of data to be 8X401 to access I/O devices for either a
interrupt, or RESET. 1M can also be set or used for the operation. After the ALU opera- source or destination specified within the
cleared by a write to the status register. tion, the data is left-rotated back to the instruction. Register addresses 13, 15, and
original position prior to merging the data in 16 specify banks A, B, and C, respectively,
Bit 1: (HZ) - This bit is set whenever the
the destination register. whereas addresses 11, 12, and 14 specify
ALU output data is not equal to zero after any
bank pairs AB, CA, and BC, respectively
of the following instructions: MOVE, ADD, When the L field specification is 0 Ondicating (Table 4). One bank of each pair is known as
AND, XOR, ADD IMMEDIATE, AND IMMEDI- a full 8-bit operation), the left-rotate. is sup- the preferred bank. The preferred banks for
ATE, XOR IMMEDIATE, or ADD WITH CAR-
December 17, 1986 6-34
pairs AB, CA, and BC are banks A, C, and B, Example 1: PROGRAM COUNTER STACK
respectively. The first letter from each bank The 8X401 stack is capable of saving up to
OPCODE L S R 0
pair can serve as a mnemonic aid as to which four return addresses for subroutines and
ADD I 4 R1 R11
bank is the preferred bank. Having a pre- interrupts. Addresses are pushed onto the
ferred bank is simply a method of determining Bank Pair
stack as a result of a call or a maskable or
which bank to read when an instruction would AB
non-maskable interrupt. Addresses are
otherwise indicate that two banks should be 6 2 popped from the stack as a result of an
read at once. unconditional RETURN, a satisfied condition-
R1 I a I c I Ie
When used as a source, the appropriate If a al RETURN, or a Pop Stack and Jump
bank is enabled and data is read from the Specified instruction. The status of the stack (whether
a
activated If device on that bank. The If a Subfield empty, full, or neither) is available from the SE
device may have been activated by a previ- Source register R1. Note specified and SF flags in the status register and the
ous address select instruction where regis- subfield from L ~ 4 and R ~ 2. Interrupts Receivable (IR) output pin.
ters C-E were the specified destination. If a
bank pair (addresses 11, 12, or 14) is speci- R1+ RO I a' I b' I c' I d' I e' I f' I g' I h' I
fied as a source, only data from the preferred INTERRUPTS
bank of that pair will be read in. Add R1 with RO (AUX). Result after
left~rotate.
Interrupt (INT)
When addresses 11 - 16 are specified as the The interrupt input is tested once each in-
destination address, the destination data is struction cycle, during the fourth quarter cycle
Bank A I i i i Ikl1lmlnlolp I (see Figure 1). When the interrupt input is
sent to the DA bus. The Write Control (WC)
signal goes high, indicating data (as opposed Read preferred bank A of AB. taken low and is enabled, the address of the
to an address) is on the DA bus and is to be next instruction is pushed onto the program
a
written to the activated If device on the
Bank A
counter stack.
selected bank(s). Program flow is transferred to address 2 for
Bank B
When addresses 11 - 16 are specified as the the start of the service routine (Figure 2). This
destination and the "L" field is not zero, the Result after merge. Data put out is accomplished by inserting a dummy in-
on both banks A and B. struction cycle after the interrupt is accepted.
following statements apply: If the source is a
register and the destination is a single bank, If, however, the specified source is a bank or The interrupt mask bit (R17, bit 0) is set
the bank will be read (or the preferred bank of bank pair, any unspecified bits will contain automatically as part of the interrupt re-
a bank pair will be read) to obtain the data unprocessed data from the source If de- a sponse.
required to perform the merge operation. The vice. Below is an example of the outcome
result is that processed data from the speci- with Source = R14 (bank pair BC) and Desti- The Interrupts Receivable (IR) pin indicates
fied subfield of the source register is returned nation = R13 (bank A). whether an interrupt applied at any point in
to that selected field of the destination bank time will be serviced. Interrupts are receivable
Example 2: when the interrupt mask is clear and the
and any bits outside of the specified subfield
will be loaded with unprocessed data from the OPCODE L S R 0 stack is not full (1M = 0 and SF = 0).
a
If device just read. If the destination is a ADD
I
4 R14 R13 Non-Maskable Interrupt (NMI)
bank pair, the data from the procedure just Bank Pair Bank A The function of the non-maskable interrupt is
described is sent to both banks. Below is an BC similar to the standard interrupt, except that
example of the outcome of an ADD instruc- the interrupt receivable status has no effect
tion with Length = 4, Rotate = 2, 7 6 5 4 3 2 0
on its operation and the address jumped to is
Source = R1, and Destination = R11 (bank Bank B I a I b I c I die I f I I h I 1 rather than 2 (Figure 2). Address 1 should
pair AB). contain an unconditional JUMP to the start of
Specified the NMI service routine. An NMI is triggered
Subfield
by a falling edge on the NMI input. The
Read Preferred bank B of Be. Note interrupt mask is set to prevent normal inter-
specified subfield from L = 4 and
R ~2. rupts from interfering with the NMI service
routine. Note that it may not always be
possible to recover from an NMI, since the
Bank B + RO I a' I b' I c' I d' I e' I f' I g' I h' I condition of the interrupt mask prior to the
Add bank B data with RO (AUX). NMI is not known, and the NMI response may
Result after left-rotate. overflow the stack.
Bank A I a I b I c' I d' I e' I f' I g I h I SLOW CLOCK REQUEST (SCR)

Result after merge. Unspecified This control input is sampled during the first
bits contain original source data. quarter cycle of each instruction along with
the instruction data. If the input is low, it will
cause the current instruciion to be executed
at half of the normal clock rate. The purpose
of this function is to facilitate accesses to I/O
devices that cannot operate at the 8X401's
December 17, 1986 6-35

full speed, without the need to run the 8X401 HALT operation. Like MCLK, RWC continues the first instruction from program storage at
continuously at half speed. to operate during a HALT operation. address O. Only MCLK, RWC, and the ad-
dress bus are in operation during the dummy
cycle. The first active instruction cycle will
HALT RESET LOGIC begin following the first MCLK after RESET is
The HALT input is sampled during the first The RESET pin is used to initialize the 8X401. released. The instruction at address 0 should
quarter cycle of each instruction. If the HALT When RESET is low, the address outputs be an unconditional jump to the beginning of
input is low, the instruction cycle is not (A 12 - AO) are high impedance, the stack the main program (which may be proceeded
executed. The MCLK continues to operate pointer is set to the top of the stack (empty), by a power-up sequence to initialize the
normally (high every fourth quarter cycle), MCLK is inhibited, RWC is low, and the system (Figure 2).
even though program execution has ceased. interrupt mask (bit 0, register 17) is se\.
If RESET is applied during program execu-
When the HALT input goes high, program
When RESET is released, the address out- tion, its effect is immediate. That is, if MCLK is
execution will resume at the next falling edge
puts all go low (program address 0). A dummy high, it may be prematurely terminated by
of MCLK. The DA bus is also inactive during a
instruction cycle occurs to allow time to fetch RESET.
Table 1_ Hexadecimal Addresses and Source/Destination Specification

ADDRESS DESIGNATION S D ADDRESS DESTINATION S D
00 RO (AUX) - General Purpose 1 X X 10 R10 -Carry6 X X
01 R1 - General Purpose X X 11 R11 - Bank Access Command (Bank Pair AB) X x
02 R2 - General Purpose X X 12 R12 - Bank Access Command (Bank Pair CAl X x
03 R3-General Purpose X X 13 R13 - Bank Access Command (Bank A) X x
04 R4-General Purpose X X 14 R14 - Bank Access Command (Bank Pair BC) X x
05 R5-General Purpose X X 15 R15 - Bank Access Command (Bank B) X x
06 R6-General Purpose X X 16 R16 - Bank Access Command (Bank C) X x
07 R7-General Purpose X X 17 Rl? - Status4 X X
08 R8-General Purpose X X 18 R18 - Suppress Left-Rotate5 X
09 R9-General Purpose X X 19 R19 - Left-Rotate 1 Place 5 X
OA RA - General Purpose X X 1A R1A - Left-Rotate 2 Places 5 X
OB RB - General Purpose2 X X 1B R 1B - Left-Rotate 3 Places 5 X
OC RC - Address Reg (Bank A) X X 1C R1C - Left-Rotate 4 Places5 X
00 RD-Address Reg (Bank B) X X 10 R1 0 - Left-Rotate 5 Places 5 X
OE RE - Address Reg (Bank C) X X 1E R 1E - Left-Rotate 6 Places5 X
OF RF - General Purpose 3 X X 1F R 1F - Left-Rotate 7 Places5 X
NOTES:
1. Also used as implied second operand for two operand instructions.
2. Also used as implied source for XEC instructions.
3. Also used as implied destination for XOR IMMEDIATE and AND IMMEDIATE instructions.
4. Certain bits in the status register are read-only. (See Status Register within text.)
5. The result is returned to the register address specified by the source field.
6. Carry register, bit 0 is the carry bit. Bits 1 - 7 are always set to zero.
December 17, 1986 6-36

Table 2. Various of Instruction Types Instruction Set Overview: The 8X401 in-
!....
struction set is summarized in Table 2. Sub-
INSTRUCTION sets of each instruction type are grouped
VARIATION OPCODE X XS DESCRIPTION
TYPE together showing the variations of each in-
MOVE MOV 0000 - - MOVE struction type. The hardware and software
descriptions can be found in the data opera-
ADD ADD 0001 - - ADD tions section.
ADC 0101 - - ADD with CARRY
AD8 1000 - - ADD IMMEDIATE 8
AD5 1001 - - ADD IMMEDIATE 5
AND AND 0010 - - AND
AN8 1010 - - AND IMMEDIATE 8
AN5 1011 - - AND IMMEDIATE 5
XOR XOR 0011 - - Exclusive-OR
XR8 1100 - - Exclusive-OR IMMEDIATE 8
XR5 1101 - - Exclusive-OR IMMEDIATE 5
XEC XEC 0100 - - EXECUTE
XMIT XT8 0110 - - Transmit IMMEDIATE 8
XT5 0111 - - Transmit IMMEDIATE 5
RETURN RIF NS 1110 000 - RETURN IF SI = 0
RIF S 1110 001 - RETURN IF SI = 1
RIF NC 1110 010 - RETURN IF CARRY = 0
RIF C 1110 011 - RETURN IF CARRY = 1
RIF Z 1110 100 - RETURN IF ALU = 0
RIF NZ
PSJ
1110
1110
101
110
-
-
RETURN IF ALU 0
POP STACK and JUMP
'*
RTN 1110 111 00 RETURN
RCC 1110 111 10 RETURN and CLEAR CARRY
RSC 1110 111 11 RETURN and SET CARRY
JUMP JIF NS 1111 000 - JUMP IF SI =0
JIF S 1111 001 - JUMP IF SI = 1
JIF NC 1111 010 - JUMP IF CARRY = 0
JIF C 1111 011 - JUMP IF CARRY = 1
JIF Z 1111 100 - JUMP IF ALU = 0
JIF NZ
JSR
1111
1111
101
110
-
-
JUMP
JUMP
IF
to
'*
ALU 0
SUBROUTINE
JMP 1111 111 - JUMP
December 17, 1986 6-37

Table 3. 8X401 Instruction Formats Table 4. I/O Acess Register

INPUT OUTPUT
REGISTER
1. Format for the MOVE, ADD, XOR, and ADD with Carry Instructions: BANK BANK
I I I I I I I I I I I I IDESTINATION
I I I I I
I OPCODE L SOURCE R
11
12
A
C
A&B
C&A
13 A A
2. Format for the XMIT 8 and ADD Immediate 8 Instruction: 14 B B&C
I I I I
?PCODE
II I
L
I I I II
DESTINATION
I I I
DATA8
I 15
16
B
C
B
C
3. Format for the XMIT 5 and ADD Immediate 5 Instruction:

I I I I I I IDESTINATION
I I I I I I I I I I I
I OPCODE L R DATA5
4. Format for the AND Immediate 8, and XOR Immediate 8 Instruction:

I I I I I I I I I
I ?PCODE
I I I I
L SOURCE DATA8
5. Format for the AND Immediate 5 and XOR Immediate 5 Instruction:

I I I I
OPCODE
II I
L
I I I I
SOURCE
I I
R
I I I I
DATA5
6. Format for the JUMP, Subroutine Jump, Conditional Jump, and Conditional
Return Instruction:
I I I I I I I I I I
I OPCODE X ADDRESS
7. Format for the Unconditional Return, Return and Set Carry, and Return and Clear
Carry Instruction:
I I I I I I I I I I
OPCODE X (UNUSED
8. Format for the XEC Instruction:

I I I I I I I I I I
I OPCODE L ADDRESS
I----INPUT PHASE---+---OUTPUT P H A S E - j
I tst I 2nd I 3rd I 4th-l

I-- QUARTER -I-- QUARTER -I--- QUARTER -I--- QUARTER
INPUT INSTRUC- GENERATE NEW PROCESS DATA LATCI:t 110 ENA·
TION, DECODE ADDRESS FOR THRU ALU, GEN- BLlNG ADDRESS
INSTRUCTION, NEXT INSTRUC- ERATE SIGNALS, OR VO DATA IN10
AND IF TION, LATCH AND AND SETUP 110 saECTED
REQUIRED, PROCESS INPUT DATA FOR OUT· PERIPHERALS.
FETCH NEW DATA. PUT. STACK PC UPDATED.
DATA. OPERATION
(EITHER PUSH,
POP, OR NOP).
Figure 1. Instruction Cycle and MCLK with: Clock Input = 26.67MHz and Cycle Time = 150ns
December 17, 1986 6-38

DATA OPERATIONS OF THE 8X401 (See Tables 2 and 3)
MOVE, ADD, AND, XOR, ADD with CARRY

SOURCE PRE-ALU ALU POST-ALU DESTINATION
AO ~ A 17 as specified by
"5" field of instruction.
- Right rotate as specified
by "R" field of instruction.
- Perform appropriate ALU

operation. (Note 1)
MOVE, ADD, AND, XOR, ADD with CARRY (Using left-rotate override R18 - R1 F)
- Left-rotate and mask as
specified by the "R" and
- RO - R 17 as specified by
the "Destination" field of
instruction. (Notes 2 & 3)
,---------,
RO - R17 as specified by
"S" field of instruction.
-
Right-rotate as specified
by "R" field of instruction.
operation. (Note 1)
- Left-rotate and mask as

specified by the "D" and
(Note 4)
When R18-R1F are
specified in the "D" field,
data is returned to the
address specified in the
"Source" field.
XMIT 8 (XT8), ADD IMMMEDIATE 8 (AD8), AND IMMEDIATE 8 (AN8), XOR IMMEDIATE 8 (XR8,..:-)_ _ _ _ _--,
One to eight bit constants
from data field of
instruction and register!
address specified by either
the source or destination
field.
- NOP.

operation. (Note 5)
-
Mask as specified by the
"L" field.
- XT8, AD8: Results are
sent to register! address,
starting from LSB,
specified by the destination
field of the instruction
word.
AN8, XR8: Results are sent
to RF, starting from LSB.
XMIT 5 (XT5), ADD IMMMEDIATE 5 (AD5), AND IMMEDIATE 5 (AN5), XOR IMMEDIATE 5 (XR5)
,----------,
One to five bit constants
from data field of
instruction and register!
address specified by either
the source or destination.
- Right-rotate as specified
by "R" field, the data
defined in either the
source or destination field.
operation. (Note 6)
- Left·rotate and mask as
specified by the "R" and
"L" fields.
- XT5, AD5: Subfield is
merged into register!
address specified by
destination field. LSB of
data field is sent to bit
position of destination
defined by "A" field.
AN5, XR5: Subfield is
merged into register!
address specified by
source field. The "A" field
specifies the LSB position
of source and RF. Results
are returned to RF.
ALL CONDITIONAL AND UNCONDITIONAL RETURNS

ADDRESS REGISTER (AR) PROGRAM COUNTER (PC) STACK
Conditional Returns: If condition is true. PC~AR. Conditional Returns: If condition is true.
AR = address from top of stack, else load address from POP stack, else NOP.
instruction word. Unconditional Returns: POP stack.
Unconditional Returns: AR = address from top of
stack.
ALL CONDITIONAL JUMPS, POP STACK AND JUMP (PSJ), and JUMP (JMP)
ADDRESS REGISTER PROGRAM COUNTER STACK
Conditional Jumps: If condition is true. PC=AR. Conditional Jumps: NOP.
AR = instruction word address, else AR = PC + 1. PSJ: POP stack.
PSJ and JMP: AR = instruction word address. JMP, NOP.
December 17, 1986 6-39

DATA OPERATIONS OF THE 8X401 (Continued)

CALL (JSR), INTERRUPT (INT), NON-MASKABLE INTERRUPT (NMI)
ADDRESS REGISTER STACK PROGRAM COUNTER
JSR: AA .. instruction address. PUSH PC + 1. (Note 6) PC~AR.
INT: AR = address 2.
NMI: AR '" address 1.
XEC
ADDRESS REGISTER PROGRAM COUNTER STACK
Right-most L bits of RS merged into corresponding bits PC not updated. NOP.
in instruction address
NOTES:
1. ALU Descriptions:
MOVE: • No operation
ADD: • Source data ADDed to contents of auxiliary register (RD - AUX). Carry bit set if carry is generated at MSB of selected data field.
NZ status bit set jf specified bits are not zero after ALU add.
AND: • Source data ANDed to contents of AUX register. NZ status bit updated accordingly.
XOR: • Source data Exclusive-ORed with contents of AUX register. NZ status bit set accordingly.
ADD with CARRY: • Sum is formed from source data. AUX register, and carry bit (register 10, bit 0). Carry and NZ status bits are set when
appropriate.
2. Left-rotate is suppressed when destination is AO (AUX).
3. When address registers Re, AD and RE are specified in the destination, source data will also go out on banks A, B, C, respectively. The L-field
should be zero (a full a-bit operation) to ensure duplication of the two outputs.
4. A left-rotate of 0 - 7 bits will correspond to R18 - R1F as specified in the "Destination" field of instruction word.
5. ALU Descriptions:
XMIT: • Input constants from the instruction word to specified destination. NZ flag is not updated when an XMIT is performed: however,
NZ can be written to by an XMIT if R17 bit 1 is within the destination field.
ADO IMMEDIATE: • Instruction word data is ADDed to data specified by destination tied. The carry bit is set if a carry is generated at the MSB of
the selected data field. NZ status bit is updated to reflect the value of "L" bits of data atter the addition.
AND IMMEDIATE: • Instruction word data is ANDed to data specified by source field. Returning the destination data to RF allows the operation to
be performed without destroying the original data field. This will facilitate testing of data for certain pre~defined values while still
preserving the original data for other uses. NZ status bit updated accordingly. Unspecified bits in RF remain unchanged.
XOR IMMEDIATE: • Sarne as AND IMMEDIATE, except the logical operation performed is Exclusive-OR.
6. Note that the stack operation IS show before the PC in the CALL and INTERRUPT formats. This is because the stack is actually in operation in
cycle 3, and the PC is updated in cycle 4 (see Figure 1). In fact, for the Call (JSR) instruction and interrupt servicing, cycle order is important for
the user to understand the current status of the PC. The other instructions are in reverse order for visual simplicity in keeping with block diagram
flow, and cycle order is irrelevant.
RESET VECTOR • The RESET VECTOR. LOCATED AT ADDRESS 0, WILL BE

AN UNCONDmONAL JUUP TO THE BEGINNING OF THE
NUl VECTOR UAlN PROGRAU.
• THE NON-UASKABLE INTERRUPT (NUI~ VECTOR,

INTERRUPT LOCATED AT ADORESS 1, IS A JUUP TO THE NUl SERV.
SERVICE ROUTINE SERVICE ROUTINE.
• LOCATED AT ADDRESS 2 IS THE ROUTINE THAT

SERVICES INTERRUPT (INT) CALLS.
NIII SERVICE
ROUTlN~
MAIN
PIIOGIIAII
8K
Figure 2. Typical 8X401 System Memory Map
December 17, 1986 6-40

Thermal Junction Temperature

vs Airflow 31
The ceramic package used for the 8X401 has 30

no heat sink and a 8ia rating of 30.5°C/W in 29
still air. Currently, to ensure operation at 28
150ns, the junction temperature of the de- 27
vices must be kept below 115°C. The maxi- 26
mum power dissipation at that junction tem- 25
perature will be 2.4W so that airflow will be '10
2.
required for full commercial range operation. 23
The 0ja versus Airflow curve is drawn here: 22
21
20
19
18
100 200 300 400 500 600 700 800
AIRFLOW (UNEAR FEET PER MINUTE)
DC ELECTRICAL CHARACTERISTICS Commercial Part 4.75V';;; Vcc';;; 5.25V, O°C';;; TA ,;;; 70°C'
LIMITS
SYMBOL PARAMETER TEST CONDITIONS UNIT COMMENTS
Min Typ Max
Vee Supply voltage 4.75 5 5.25 V
VIH High-level input voltage 2 V
Vil Low-level input voltage 0.8 V

DAO through DA7, MCLK,
Vee = Min, 10H = -3mA 2.4 V
High-level output voltage SC, WC, AB, BB, CB
VOH
Vee = Min, 10H = -4OOI1A 2.4 V All others
DAO through DA7, MCLK,
Vee = Min, 10l = 16mA 0.5 V
RWC, SC, WC, A, S, C
VOL Low-level output voltage
AO through A 12, PS, NZ,
Vee = Min, 10l = 8mA 0.5 V
CY,IR
Vie Input clamp voltage Vee = Min, liN = -10mA -1.5 V
IIH High-level input current Vee = Max, VI = 2.7 20 I1A

III Low-level input current Vee = Max, VI = O.4V -400 I.lA
Off-state output current,
10ZH Vee = Max, Vo = 2.7V 50 I1A DAO through DA7
high-level voltage applied
Off-state output current
10Zl Vee = Max, Vo = O.4V -400 I1A DAO through DA7
low-level voltage applied
Short circuit output cur-
los Vee = Max, Vo = OV -30 -140 mA
rent 2
500 mA TA = O°C; Cold start 3
Icc Supply Current Vee = Max
430 mA TJ=115°C
NOTES:
1. 64-pin CDIP, airflow required for commercial operation. (The plastic 64-pin DIP with internal heatsink does not have this requirement.)
See above for thermal characteristics.
2. Not more than one output should be tested at a time.
3. Guaranteed by operation to Icc measured at 25°C.
December 17, 1986 6-41

AC ELECTRICAL CHARACTERISTICS (Vcc=5V +5%, 0°C";;TA ";;70°C)1
150n5 CYCLE > 150n5 CYCLE

SYMBOL PARAMETER UNIT COMMENTS
tpc Processor cycle time 150 ns
tcp Clock pulse period 37.5 ns
tCH Clock pulse high time 15 ns See Note 2
tCl Clock pulse low time 15 ns
tMCl CPl to MCLK low 30 ns See Note 2
tMCH CP4 to MCLK high 40 ns
tw MCLK pulse width 25 31 38 T40 -12 T40 ns
tRWCl CPl to RWC low 34 40 ns
tRWCH CP3 to RWC high 40 ns
T30 +T40 T30 + T40
tRWCW RWC pulse width 65 75 80 ns
-10 +5
tAS CP2 to address stable 52 ns
tMAS MCLK to address stable 62 Tl0 + 24 ns
tiS Instruction setup to CPl 0 ns See Note 3
tMIS Instruction setup to MCLK 25 ns
tlH Instruction hold from CP2 20 ns
tMIH Instruction hold from MLCK 25 Tl0-12 ns
tSCH CP3 to SC rising edge 45 ns
Tl0 + T20
tMscH MCLK to SC rising edge 95 ns
+20
tWCH CP3 to WC rising edge 55 ns
Tl0 +T20
tMWCH MCLK to WC rising edge 105 ns
+20
tWl CPl to SC/WC falling edge 35 ns See Note 4
tMWl MCLK to SC/WC falling edge 0 ns
CPl to input phase bank signal
tlBSl 60 ns
falling edge
MCLK to input phase bank signal
tMIBSl 33 ns
falling edge
CP3 to input phase bank signal
tlBSH 45 ns
rising edge
MCLK to input phase bank signal Tl0+ T20
tMIBSH 95 ns
rising edge + 20
CP3 to output phase bank signal
tOBSl 53 ns
falling edge
MCLK to output phase bank signal Tl0 +T20
tMOBSl 105 ns
falling edge +30
CPl to output phase bank signal
tOBSH 46 ns
rising edge
MCLK to output phase bank signal
tMOBSH 0 20 ns
rising edge
tlDS Input data setup to CP3 -3 ns
25 - T10
tMIDS Input data setup to MCLK -50 ns
-T20
tlDH Input data hold from CP3 28 ns
T10 +T20
tMIDH Input data hold from MCLK 78 ns
+3
toDH Output data hold from CPl 35 55 ns
tMODH Output data hold from MCLK 10 25 ns
December 17, 1986 6-42

I
[
I
!
1-
150ns CYCLE > 150ns CYCLE
SYMBOL PARAMETER UNIT COMMENTS
taos CP3 to output data stable 70 ns
T1Q+T2Q
tMOOS MCLK to output data stable 120 ns
+45
SC/WC rising edge to output driver
tOI 18 ns
turn on
tHS Halt setup to CP2 0 ns
tMHS Halt setup to MCLK -10 ns
tHH Halt hold from CP2 50 ns
tMHH Halt hold from MCLK 60 T1Q + 22 ns
tSIS Status input setup to CP1 10 ns
tMSIS Status input setup to MCLK 40 ns
tglH Status input hold from CP1 20 ns
tMSIH Status input hold from MCLK 0 ns
tscRS SCR setup to CP1 0 ns
tMSCRS SCR setup to MCLK 25 ns
See Diagram
tSCRH SCR hold from CP2 (Slow CP2) 20 ns
for CP2
tMSCRH SCR hold from MCLK 63 ST1Q-12 ns Slow T1Q
tiNTS INT setup to CP1 10 ns
tMINTS INT setup to MCLK 40 ns
tlNTH INT hold from CP1 10 ns
tMINTH INT hold from MCLK -10 ns
leyU CP4 to CY update 60 ns
tMCYU MCLK to CY update -10 28-T4Q ns
tNZU CP4 to NZ update 60 ns
tMNZU MCLK to NZ update -5 33-T4Q ns
tlRU CP4 to IR update 75 ns
tMIRU MCLK to IR update 20 58-T4Q ns
tpsu CP4 to PS update 60 ns
tMPSU MCLK to PS update -10 28-T4Q ns
Program memory access time T2Q+T3Q
tACC 60 ns
(address stable to valid instruction) + T4Q-52
I/O port output enable time T1Q+T2Q
tlO 24 ns
(bank signal to valid data on bus) -51
tRW Reset pulse width 150 tpc ns
tNMIW NMI pulse width 50 ns
tNMIS NMI setup to CP2 15 ns See Note 5
tMNMIS NMI setup to MCLK 10 ns See Note 5
NOTES:
1. Inputs swing between OV and 3V. All outputs are measured at 1.5V with loading as specified in the test circuits.
2. CP1, CP2, CP3, and CP4 refer to the clock pulse that causes the first. second, third, and fourth 8X401 quarter cycles, respectively. Parameters
referenced to MCLI<, CP1, CP2, CP3, and CP4 are measured to the falling edge of those signals. Tl Q, T2Q, T3Q, and T4Q represent time intervals
for the first, second, third, and fourth 8X401 quarter cycles. respectively. Duty cycle can be from 40% to 80%.
3. Instructions must be setup before CPl.
4. tWL represents IscL and tWCL' iMWL represents tMSCL and tMWCL·
5. This guarantees NMI is serviced in the current cycle.
December 17, 1986 6-43

TEST CIRCUIT
VL=2.3 VL=2.1V
OUTPUT
UNDER
TEST
~
R'
2260
OUTPUT
UNDER
TEST
~ R'
'000
~50PF ~'OOPF
TC11240S
MAIN TIMING DIAGRAM
CP1 CP2 CP3 CP4 CP1 CPa CPa CP4 CP1 CPa CP3 CP4 CP1 CPa CPa
I I I I I I I I I I I I I I I
CP
IICLK ---+J
AWe
I
I 1ou.s-l
ADDRESS
(A12-AO) _ _ _ _ _ _ _ _ '--------...JI'----o:----.~- '-__.....____
INSTRUCTION
(119-10) " "........... . ,
sc
--------+-~--~
tMWCL
~~ --------~-~----<'_~_A_~_~_J
,
ii
THE 3 CYCLES REPRESENT THE FOUOWING INSTRUCTIONS:

- - . r IIIIIEDIATE ADDRESS 10 BANK B (SELECT A PORT ON BANK B)
-IIOI/E BANK A DATA 10 BANK B
- ADD _ T E DATA 10 BANK A
""",,'"
December 17, 1986 6-44

TIMING SUPPLEMENT: STATUS
CP2 CP3 CP4 CP1 CP2 CP3 CP1 CP2 CP3 CP4 CP1 CP2
I I I I I I I I I I I I
CP
MCLK
~~§
~IsH ~"'~H
SI
I-t"su- I - typsu
PS }
! - - tNZU - I - tyNZU :
:
NZ
j
1-~~1 I-- tllC~
CY
I-~RUj ~""RU
IR
TIMING SUPPLEMENT: RESET
CP1 CP2 CP3 CP4 CP1

I I I I I
" '---' 1_~1

MCLK
RESET ---1 _'\1
,
AWC
ASSERTED
RESET c.-----
I tRW
ADDRESS
X CP1
)
CP2 CP3 CP4 CP1 CP2 CP3 CP4 CP1
I I I I I I I I I
CP
f-:~~=~TRUCTION-I
"---
"
MCLK
RESET
RELEASED
AWC
I \ I '---
RESET I
ADDRESS
\
ADDRESS = 0
L )(
December 17, 1986 6-45

TIMING SUPPLEMENT: HALT
CPl CP2 CP3 CP4 CPl CP2 CP3 CP4 CPl CP2 CP3 CP4 CPl
I I I I I I I I I I I I I
CP
I I
MCLK
M I I "--
RWC--i
I I
,
tHS-j
-l " ~~HS
I
~tMHH~
I-tHH
I I \..-
HALT " r---------""\ I I

SCORWC I \ I '--
( )-
DA BUS
< >
A.B.ORC
X 7 \ X )(
TIMING SUPPLEMENT: INT
CP2 CP3 CP4 CPl CP2 CP3 CP4 CPl CP2 CP3 CP4 CPl
CP
MCLK
I~ ________~__-L______________________________________________________________
ADDRESS
ADDRESS OF INSTRUCTION NOT
EXECUTED DUE TO INTERRUPT.
ADDRESS = 0002,.
\~--------------------------------------
IR
December 17. 1986 6-46

TIMING SUPPLEMENT: NMI ,..
CPl CP2 CP3 CP4 CPl CP3 CP4 CPl CP2 CP3 CP4 CPl
CP
UCLK
NMi
t,.1IIW--j
ADORESS * E S S OF INSTRUCTION
l1TED DUE TO NUl.
H!li)( ADDRESS = 0001,. X >C
IR
~
TIMING SUPPLEMENT: seR
CPl CP2 CP3 CP4 CPl CP2 CP3 CP4 CPl

1 1 1 I 1 1 1 1 1
CP
UCLK _ _ _ i:.Jrl,..1--;.:_______--J,r-------.'I--_ _ _" " - - -

fMC.! :
I~RS
l_ _
11+-!seR:
~I ~+---...JI \:
!seRS 'I IUSCR"
5 _ _ _ _ _ _ .'1 ,;-
__ -_-_-_--_-_-_-J-r---TC-_-_-_-_-J-,-------
ADDRESS
X~________~X~_________x=
\ I
\~-------------------
SCORWC---,
DABUS ( ) (~-----)~-------------
A.B.ORC~ I
_________JI
\
December 17. 1986 6-47

Signetics SCN8049 Series
SCN8049, SCN8050, SCN8039,
SCN8040 Single-Chip 8-Bit
M icrocontroller
Microprocessor Products Product Specification

The Signetics SCN8049 Series micro- • a-bit CPU, ROM, RAM, 1/0 in a
controllers are self-contained, 8-bit pro- 40-pin package
cessors which contain the system tim- • 24 quasi bidirectional 1/0 lines
ing, control logic, RAM data memory, XTAL1 Tl
• Two test inputs
ROM program memory (8048/49/50 P27
only), and 1/0 lines necessary to imple- • Internal counterltimer

ment dedicated control functions. All • Single-level vectored Interrupts: P25
SCN8049 Series devices are pin and external, counterltimer P24
program compatible, differing only in the • Over 90 instructions, 70% single P17
size of the on-board program ROM and byte P16
data RAM, as follows: • 1.3611S or 2.5!lS instruction cycle, P15

P14
TYPE RAM SIZE ROM SIZE all instructions one or two cycles
P13
• Expandable memory and 1/0
SCN8049 128 X 8 2K x 8 DBO P12
SCN8050 256 X 8 4K X 8 • Low voltage standby P11
SCN8039 128 X 8 - • TTL compatible inputs and DB2 Pl0
SCN8040 256 X 8 - outputs DB3
• Single + 5V power supply DB4 PROG

Program memory can be expanded ex- DBS P23
ternally up to a maximum total of 4K DB6 P22
bytes without paging. Data memory can LOGIC SYMBOL DB7 P21
also be expanded externally. 110 capa- Vss P20
bilities can be expanded using standard
devices or the 8243 1/0 expander.
The SCN8049 Series processors are
designed to be efficient control proces-
XTAL t: PORT
PORT
INDEX
CORNER
40
sors as well as arithmetic processors. RESET ........ 2
0 39
They provide an instruction set which SINGLE
STEP -
allows the user to directly set and reset
EXTERNAL
individual lines within its 110 ports as MEM-
PLCC
well as test individual bits within the
accumulator. A large variety of branch
and table look-up instructions make
TEST f: 17
18 28
29
these processors very efficient in imple- INTERRUPT ........ TOP VIEW

menting standard logic functions. Also, PI" Function
CD0044PS
Function
PI"
special attention has been given to code 1 NC 23 NC
2 TO 24 P20
efficiency. Over 70% of the instructions BUS
3 XTALl 25 P21
are a single byte long and all others are 4 XTAL2 26 P22
5 RESET 27 P23
only 2 bytes long. 6 ss 28 PRoo
7 INT 29 VDD
An on-chip 8-bit counter is provided 8 EA 30 Pl0
9 l'iil 31 P11
which can count, under program control, 10 j5SEfii 32 P12
either internal clock pulses (with a divide 11 WI! 33 P13
12 NC 34 NC
by 32 prescaler) or external events. The 13 ALE 35 P14
counter can be programmed to cause an 14 DBO 36 P15
15 081 37 P16
interrupt on terminal count. 16 DB2 38 P17
17 083 39 P24
18 084 40 P25
19 085 41 P26
20 086 42 P27
21 087 43 Tl
22 Vss 44 Vee
August 26, 1986 6-48 853-0095 85292

SCN8049, SCN8050, SCN8039, SCN8040

SCN8049 Series
J 1[
SCN8000 HoODOO (CPxxxx)
ROM/RAM (bytes) CUSTOM RO" PAnE'N NUMBER

35 = EXT /64 48 = 1K/64 Applies to masked ROM versions only.
39 = EXT/128 49 = 2K/128 Number will be assigned by Signetics.
40 = EXT /256 50 = 4K/256 Contact Signetics sales office for ROM
pattern submission requirements.
OPERATING TEMPERATURE RANGE 40 = Pin DIP
A = -40°C to + 85°C 44 = Pin LCC
C = O°C to +70°C
SPEED - - - - - ' ' - - - - - - PACKAGE
B = 11MHz clock N = Plastic 01 P
6 = 6MHz clock I = Ceramic DIP
A = Plastic lCC
PIN DESCRIPTION
PIN NO.
DIP PLCC
Vss 20 22 Circuit ground potential.
VDD 26 29 low power standby.
Vee 40 44 Main Power Supply: + 5V during operation.
PROG 25 28 0 Output strobe for 8243 I/O expander.
P10 - P17 27 -34 30 - 33, I/O Port 1: 8·bit quasi·bidirectional port.
35-38
P20 - P27 21-24, 24 - 27, I/O Port 2: 8·bit quasi·bidirectional port. P20·23 contain the four high·order program counter bits
35-38 39-42 during an ex1ernal program memory fetch and serve as a 4·bit I/O expander bus for 8243.
DBO-DB7 12 -19 14- 21 I/O Data Bus: True bidirectional port which can be written or read synchronously using the RD,
WR strobes. The port can also be statically latched. Contains the eight low·order program
counter bits during an ex1ernal program memory fetch and receives the addressed instruction
under the control of PSEN. Also contains the address and data during an external RAM data
store instruction, under control of ALE, RD and WR.
TO 1 2 I Input pin testable using the conditional transfer instructions JTO and JNTO. TO and be
designated as a clock output using the ENTO ClK instruction.
T1 39 43 I Input pin testable using the JT1 and JNT1 instructions. Can be designated the timer/counter
input using the STRT CNT instruction.
XTAl1 2 3 I Crystal 1: One side of the crystal input for internal oscillator. Also input for external source
(non-TTL VIH).
XTAl2 3 4 I Crystal 2: Other side of crystal input.
INT 6 7 I Interrupt: Initiates an interrupt if interrupt is enabled. Interrupt is disabled aiter a reset. Also
testable with conditional jump instruction. Interrupt must remain low for at least three machine
cycles for proper operation.
RESET 4 5 I Reset: Used to initialize the microcomputer. Active low. Internal pullup -75Kr!. During
program verification the address is latched by a "0" to "1" transition on RESET and the
data at the addressed location is output on BUS.
RD 8 9 0 Read: Output strobe activated during a bus read. Can be used to enable data onto the bus
from an ex1ernal device. Used as a read strobe to ex1ernal data memory.
WR 10 11 0 Write: Output strobe during a bus write. Used as write strobe to ex1ernal data memory.
ALE 11 13 0 Address Latch Enable: Occurs once during each cycle and is useful as a clock output. The
negative edge of ALE strobes address into ex1ernal data and program memory.
PSEN 9 10 0 Program Store Enable: Output occurs only during a fetch to ex1ernal program memory.
55 5 6 I Single Step: Can be used in conjunction with ALE to "single step" the processor through
each instruction.
EA 7 8 I External Access: Forces all program memory fetches to reference ex1ernal memory. Useful
for emulation and debug, and essential for testing and program verification.
NOTE:
Each pin on these ports can be assigned, under program control, to be an input or an output. A pin is deSignated as an input by writing a logic" 1" to the pin. RESET
sets all pins to the input mode. Each pin has an internal pullup of approximately SOkn.
August 26, 1986 6-49
SCN8049, SCN8050, SCN8039, SCN8040

SCN8049 Series
FUNCTIONAL DESCRIPTION
The following is a general functional description of the SCNB049 Series microcomputers. Refer to the block diagram below.
BLOCK DIAGRAM
P!"
RESIDENT
ROM
(8048149150 ONLy)
PQRTl P,O
8US
r--------,~----~__----~~----~~----~~----------~--~ B~:~R
LATCH
AEGISTEA2
REGISTER 3
REGISTER ..
POWER
SUPPLY BV
DD
- . RAM SUPPLY
v~ +5V MAIN SUPPLY
!!..OND
REGISTER 5
REGISTER 6
REGISTER 7
8 LEVEL STACK
(VARIABLE LENGTH)
OPTIONAL SECOND
REGISTER BANK
DATA STORE
RESIDENT
RAM ARRAY
TIMING INTERRUPT INITIALIZE EXPANDER CPU OSCILLATOR PROGRAM SINGLE READlWRITE
OUTPUT STROBE MEMORY XTAL MEMORY STEP STROBES
SEPARATE ENABLE
ADDRESS
LATCH
ENABLE
August 26, 19B6

SCN8049, SCN8050, SCN8039, SCN8040

SCN8049 Series
PROGRAM MEMORY locations are indirectly addressable by either An interrupt or CALL to a subroutine causes
Resident program memory consists of up to of two RAM pointer registers at locations 0 the contents of the program counter to be
4K bytes of ROM. The program memory is and 1. The first eight locations of RAM (0-7) stored in one of the 6 register pairs of the
divided into pages of 256 bytes each. As are designated as working registers and are program counter stack. The pair to be used is
shown in the memory map, Figure 1, program directly addressable by several instructions. determined by a 3-bit stack pointer which is
memory is also divided into two 2046-byte part of the Program Status Word (PSW). Data
By selecting register bank 1, RAM locations
banks, MBO and MB1. A total of 4096 bytes RAM locations 6 through 23 are available as
24-31 become the working registers, replac-
can be addressed directly. If more memory is stack registers and are used to store the
ing those in register bank 0 (0-7).
required, an I/O port can be used to address program counter and 4 bits of PSW. The
locations over 4095. RAM locations 6-23 are designated as the stack pointer, when initialized to 000, points
stack. Two locations (bytes) are used per to RAM locations 6 and 9. The first subroutine
There are three locations in program memory CALL, allowing nesting of up to eight subrou- jump or interrupt results in the program count-
of special importance. These locations con- tines. er contents being transferred to locations 6
tain the first instruction to be executed upon and 9 of the RAM array. The stack pointer is
the occurrence of one of three events. If additional RAM is required, up to 256 bytes
then incremented by one to point to locations
may be added and addressed directly using
LOCATION EVENT 10 and 11 in anticipation of another CALL.
the MOVX instructions. If more RAM is re-
Nesting of subroutines within subroutines can
0 Activation then deactivation quired an I/O port can be used to select one
continue up to eight times without overflowing
of the "FfEm line. (256-byte) bank of external memory at a time.
the stack. If overflow does occur the deepest
3 Activation of the liiIf line address stored (location 6 and 9) will be
when the external interrupt overwritten and lost since the stack pointer
is enabled. PROGRAM COUNTER AND
overflows from 111 to 000. It also underflows
7 An overflow of the timer/ STACK from 000 to 111.
counter if the T /C interrupt The Program Counter (PC) is a 12-bit count-
is enabled. er/register that points to the location from The end of a subroutine, which is Signalled by
which the next instruction is to be fetched. a return instruction (RET or RETR), causes
The 6046 and 6049 will automatically address the stack pointer to be decremented and the
external memory when the boundary of their contents of the resulting register pair to be
DATA MEMORY transferred to the program counter.
internal memory is exceeded. All processors
Resident data. memory, as shown in Figure 2,
access external memory if EA is high.
consists of up to 256 bytes of RAM. All
-D
255
8040/8050
USER RAM
128)(8
128
127
8039/8049
USER RAM
-B'~-
64K8
64
63 8035/8046
r---2047 - USER RAM
j SELMBO 32 32)(8
31 BANK 1 ~
'-B
WORKING DIRECTLY
REGISTERS ADDRESSABLE
~
0-
&x8
f----ii1:----
WHEN BANK 1
IS SELECTED
1023
f----iio:----
~
:;:
24
~
0 i
0- ~
23
ADDRESSED
:;: 8 LEVEL STACK
INDIRECT LY
9 'OR
z
-
8 LOCATION 7 - TIMER USER RAM THROUG H
0
i
0-
7
6
I-- INTERRUPT VECTORS
PROGRAM HERE
16)(8 R1 OR RO
(RO' OR R1')
:;: 5
1./
z
0
4
3 ~ I--
LOCATION 3- EXTERNAL
INTERRUPT VECTORS
BANKO
WORKING
~
DIRECTLY
2 PROGRAM HERE REGISTERS" ADDRESSABLE
'-- '-- ,-0

1
716151413121110 _ ~:~~TR~~C~~=~ 1--------
&x8
___ !!1 ___
RO
WHEN BANKO
ISSELErTED
ADDRESS o
p""""",
PFOO'' '
Figure 1. Program Memory Map Figure 2. Data Memory Map
August 26, 1966 6-51

SCN8049, SCN8050, SCN8039, SCN8040

SCN8049 Series
OSCILLATOR AND CLOCK

The processor contains its own internal oscil-
lator and clock driver. A crystal, inductor, or
external pulse generator may be used to
determine the oscillator frequency (see Fig-
ure 3). The output of the oscillator is divided +5V
by three and can be output on the TO pin by

executing the ENTO ClK instruction. This
Q
ClK signal is divided by 5 to define a machine INTERNAL
(instruction) cycle. It is available on Pin 11 as BUs-+--t D
ALE. D
FLIP
FLOP
...-.......=:'1XTALI
CLK Q
XTAL2
c= 15-25pF C
(INCLUDES SOCKET, I
STRAY) -=
SERIES RESONANT, AT CUT CRYSTAL
IN
DRIVING
FROM EXTERNAL
SOURCE
Figure 4_ "Quasi Bidirectional" Port Str~cture
+5V counter. External events are input directly to lines are non-latching; i.e., inputs must be
the counter. The maximum frequency that present until read by an input instruction.
470'l can be counted is one third of the frequency Inputs are fully TTL compatible and outputs
Jo-<f----...:2'1 XTAL I of the cycle counter. The minimum positive will drive one standard TTL load.
duty cycle that can be detected is 0.2 tCY.
The lines of ports 1 and 2 are called quasi-
The counter is under program control and can
470n bidirectional because of a special output
be made to generate an interrupt to the
Circuit structure which allows each line to
processor when it overflows.
serve as an input, an output, or both even
BOTH XI AND X2 SHOULD BE DRIVEN. though outputs are statically latched. Figure 4
RESISTORS TO VCC ARE NEEDED TO ENSURE
shows the circuit configuration. Each line is
~Ill=':i:YJ~~T~lg~~~IJ~~~S~I~~~UM LOW INTERRUPT continuously pulled up to + 5V through a
TIMES ARE 45%. An interrupt may be generated by either an
resistive device of relatively high impedance
external input (I NT, Pin 6) or the overflow of
(--SOK). This pullup is sufficient to provide the
the internal counter, when enabled. In either
LC source current for a TTL high level yet can be
OSCILLATOR case, the processor completes execution of
MODE
pulled low by a standard TTL gate thus
the present instruction and then does a CAll
rr ,: : :;,
allowing the same pin to be used for both
to the interrupt service routine. After service,
input and output. To provide fast switching
C NOMINAL I
a RETR instruction restores the machine to
times in a "0" to "1" transition a relatively
45.H 20pF ---s:2iiiiZ f I the state it was prior to the interrupt. The
low impedance device (--SOKQ) is switched
'-~'
external interrupt has priority over the internal
in momentarily (--SOOns) whenever a "1" is
interrupt.
written to the line. When a "0" is written to
the line, a low impedance (--{3000Q) device
-= c CPP _ 5-IOpF
INPUT/OUTPUT
overcomes the light pullup and provides TTL
3 XT AL2 PIN·TO.PIN current sinking capability.
CAPACITANCE The processor has 27 lines which can be
EACH C SHOULD BE APPROXIMATELY 2OpF, used for input or output functions. These lines Since the pulldown transistor is a low imped-
INCLUDINCl STRAY CAPACITANCE. are grouped as 3 ports of 8 lines each which ance device a "1" must first be written to any
serve as either inputs, outputs or bidirectional line which is to be used as an input. Reset
Figure 3, Crystal Oscillator Mode ports and 3 "test" inputs which can alter initializes all lines to the high impedance "1"
program sequences when tested by condi- state. This structure allows input and output
tional jump instructions. on the same pin and also allows a mix of
input lines and output lines on the same port.
Ports 1 and 2 The quasi-bidirectional port in combination
TIMER/EVENT COUNTER Ports 1 and 2 are each 8 bits wide and have
An internal counter is available which can with the ANL and ORl logical instructions
identical characteristics. Data written to these
count either external events or machine cy- provide an efficient means for handling single
ports is statically latched and remains un-
cles (7 32). The machine cycles are divided line inputs and outputs within an 8-bit proces-
changed until rewritten. As input ports these
by 32 before they are input to the 8-bit sor.
August 26, 1986 6-52

SCN8049, SCN8050, SCN8039, SCN8040

SCN8049 Series
POWERSUPPLY ~
+5V
PROCESSOR I ,
INTERRUPTED I I
POWER SUPPLY - - - - - , i
I NORMAL POWER
FAIL SIGNAL L--...i..--..I----- ON SEQUENCE
ACTIVE
I
I I
I I
IFOLLOWS
PULLUP
RESET 1___Li------
EXTERNAL RESET DATA SAVE ACCESS TO
ROUTINE DATA RAM
EXECUTED INHIBITED
+5V
Figure 6. Power Down Sequence
RESET INPUT A typical power down sequence occurs as

The reset input provides a means for initial- shown in Figure 6.
ization for the processor. This Schmitt-trigger
input has an internal pullup resistor which in
POWER ON RESET
combination with an external 1j.lF capacitor INSTRUCTION SET
provides an internal reset pulse of sufficient The SCN8049 Series instruction set consists
Figure 5. Reset Circuits length to guarantee all circuitry is reset. If the of over 90 one and two byte instructions (see
reset pulse is generated externally, the reset Table 1). Program code efficiency is high
pin must be held at ground (0.5V) for at least because: (1) working registers and program
10 milliseconds after the power supply is variables are stored in RAM, which require
BUS
within tolerance. Only five machine cycles only one byte to address and (2) program
BUS is also an 8·bit port which is a true
(12.5j.ls @ 6MHz) are required if power is memory is divided into pages of 256 bytes
bidirectional port with associated input and
already on and the oscillator has stabilized. each, which means that branch destination
output strobes. If the bidirectional feature is
Typical circuitry is shown in Figure 5. addresses require one byte.
not needed, BUS can serve as either a
statically latched output port or non-latching The instruction set efficiently manipulates and
input port. Input and output lines on this port tests bits in addition to performing logical and
cannot be mixed. SINGLE STEP arithmetic operations upon and the testing of
By proper control of the SS line, the mircro- bytes. A set of move instructions operates
As a static port, data is written and latched computer can be made to execute one in- indirectly upon either RAM or ROM, which
using the OUTL instruction and input using struction and then pause or wait until the permits efficient access of pointers and data
the INS instruction. The INS and OUTL in- single step switch is activated again. tables. The indirect jump instruction performs
structions generate pulses on the corre-
a multi (up to 256) way branch upon the
sponding RD and WR output strobe lines;
content of the accumulator to addresses
however, in the static port mode they are POWER DOWN MODE stored in a lookup table. The "decrement
generally not used. As a bidirectional port, the The SCN8049 Series devices permit power to register and jump if not zero" instruction
MOVX instructions are used to read and write be removed from all but the data RAM array saves a byte every time it is used versus
to the port. A write to the port generates a for low power standby operation. In the power using separate increment and test instruc-
pulse on the WR output line and output data down mode the contents of data RAM can be tions.
is valid at the trailing edge of WR. A read of maintained while drawing typically 5 % of
the port generates a pulse on the RD output normal operating power. The on-chip counter enables either external
line and input data must be valid at the trailing events or time to be counted off-line from the
edge of RD. When not being written or read, Vee serves as the 5V supply pin for the bulk main program. The processor can either test
the BUS lines are in a high impedance state. of the circuitry while the VDD pin supplies only the counter (under program control) or cause
the RAM array. In normal operation both pins its overflow to generate an interrupt. These
Test and INT inputs are at + 5V. In standby, Vee is at ground and features are highly desirable for real time
Three pins serve as inputs and are testable only VDD is maintained at its specified volt- applications. See Table 2 for instruction tim-
with the conditional jump instruction. These age. Applying RESET to the processor ing.
are TO, Tl, and INT. These pins allow inputs through the RESET pin inhibits any access to
to cause program branches without the ne- the RAM by the processor and guarantees
cessity to load an input port into the accumu- that RAM cannot be inadvertently altered as
lator. The TO, Tl, and INT pins have other power is removed from Vce.
possible functions as well.
August 26, 1986 6-53

SCN8049, SCN8050, SCN8039, SCN8040

SCN8049 Series
ABSOLUTE MAXIMUM RATINGS 1

TA Operating ambient temperature 2 range
SCN80xxHC o to + 70 "C
SCN80xxHA -40 to +85 "C
TSTG Storage temperature range -65 to + 150 "C
VIN Input voltages with respect to Vss 3 -0.5 to + 7 V
DC ELECTRICAL CHARACTERISTICS TA = O"C to 70"C, Vee = Voo = 5V ± 10%, Vss = OV 4 , 5, 6
LIMITS
SYMBOL PARAMETER TEST CONDITIONS 7 UNIT
Min Typ Max
VIL Input low-voltage
All except XT AL 1, XT AL2 -0.5 0.8 V
VIU XTAL1, XTAL2 -0.5 0.6 V
VIH Input high voltage

All except RESET, 2.0 Vee V
XTAL1, XTAL2
VIH1 RESET, XTAL1, XTAL2 3.8 Vee V
VOL Output low-voltage IOL = 2,OmA 0.4 V
VOH Output high-voltage

All except BUS IOH = -125iJA 2.4 V
BUS IOH = -400/lA 2.4 V
ILl1 Port1, Port2, EA, SS Vss + 0.45 < VIN < Vee -500 /lA
Iu Tl, Tnt Vss + 0.45 < VIN < Vee ±10 /lA
ILl2 RESET Vss + 0.45 < VIN < Vee -10 -300 /lA
IOL Output leakage current

BUS, TO (high inpedance state) Vss + 0.45 < VIN < Vee ±10 /lA
100 Standby supply current RESET<VIL
8035/8048 All inputs = OV 2.5 mA
8039/8049 Vee = OV 4.5 mA
8040/8050 8,5 mA
100 + Icc Total supply current RESET <VIL
8035/8048 45 80 mA
8039/8049 50 95 mA
8040/8050 60 110 mA
Voo Standby power supply 2.5 V
TA = -40 to 85"C, Automotive temperature range 8
VIH Input high voltage
All except XTAL 1 and XT AL2 2.2 V
VIH1 RESET, XTAL 1, XTAL2 4.0 V

Input leakage current
Ilu Portl, Port2, EA, SS Vss +.45 < VIN < Vee -750 /lA
ILl2 RESET Vss + .45 < VIN < Vce -5 -300 iJA
100 Standby supply current
8035/8048 RESET <VIL 3.75 mA
8039/8049 All inputs = OV 6.75 mA
8040/8050 Vee = OV 12.75 mA
Icc + 100 Total supply current
8035/8048 RESET <VIL 90 mA
8039/8049 105 mA
8040/8050 120 mA
August 26, 1986 6-54

SCN8049, SCN8050, SCN8039, SCN8040

SCN8049 Series
AC ELECTRICAL CHARACTERISTICS TA = O·C to 70·C, vcc = voo = 5V ± 10%, Vss = Ov4, 5, 6
11 MHz 6 MHz
TEST VERSIONS VERSIONS
CONDITIONS7
Min Max Min Max
(Refer to Figures 7, 8 and 9)
tLL ALE pulse width 150 400 ns
tAL Address setup to ALE 70 150 ns
tLA Address hold from ALE 50 80 ns
tcc Control pulse width (PSEN, 300 700 ns
RD, WR)
tow Data setup before WR 250 500 ns
two Data hold after WR 40 120 ns
tCY Cycle time 1.36 3.75 2.5 15.0 Ils
tDR Data hold 0 100 0 200 ns
tRO PSEN, RD to data in 200 500 ns
tAW Address setup to WR 200 230 ns
tAO Address setup to data in 400 950 ns
tAFC Address float to RD, PSEN -10 0 ns
tCA Control pulse to ALE 10 10 ns
(Refer to Figure 10)
tcp Port control setup before 100 110 ns
falling edge of PROG
tpc Port control hold after falling 60 130 ns
edge of PROG
tpR PROG to time P2 input must 650 810 ns
be valid
top Output data setup time 200 250 ns
tpo Output data hold time 20 65 ns
tPF Input data hold time 0 150 0 150 ns
tpp PROG pulse width 700 1200 ns
tpL Port 2 110 data setup 250 350 ns
tLP Port 2 110 data hold 20 150 ns
NOTES:
1. Stresses above those listed under absolute maximum ratings may cause permanent damage to the device. This is a stress rating only and functional operation of
the device at these or any other condition above those indicated in the operation section of this specification is not implied.
2. For operating at elevated temperatures. the device must be derated based on + 150°C maximum junction temperature.
3. This product includes circuitry specifically designed for the protection of its internal devices from damaging effects of excessive static charge. Nonetheless, it is
suggested that conventional precautions be taken to aviod applying any voltages larger than the rated maximum.
5. All voltage measurements are referenced to ground (VsS>. For testing, all input signals swing between 0.4V and 2.4V with a transition time of 20ns maximum. All
time measurements are referenced at input voltages of 0.8V and 2.0V and output voltages 0.8V and 2.0V as appropriate.
6. Typical values are at + 25·C, typical ssupply voltages and typical processing parameters.
7. Control outputs: CL - 80pF
Bus outputs: CL = 150pF
Icv = 1.36jlS for 11 MHz versions
lev = 2.5jlS for 6 MHz versions
S. Where no specification is shown, the commercial temperature range specification applies.
1.2
~
u 1.1
"'-
Q
+
0
.g 1.0
III
N
:J
"'- ~
c 0.9
lIE
""
a:
0
z o.a
0.7
-25 25 50 75 100
TEMPERATURE, ·C
NORMALIZED TOTAL
SUPPLY CURRENT
VI. TEMPERATURE (TYPICAL)
August 26, 1986 6-55

SCN8049, SCN8050, SCN8039, SCN8040

SCN8049 Series
TIMING DIAGRAMS
I-tLL-!
-------t cv- - - - - - .I
ALE
Figure 7. Instruction Fetch From External Program Memory
ALE .J \'------
BUS FLOATING FLOATING
Figure 8. Read From External Data Memory
ALE J \'------- \
BUS FLOATING FLOATING
Figure 9. Write to External Data Memory
August 26, 1986 6-56

SCN8049, SCN8050, SCN8039, SCN8040

SCN8049 Series
TIMING DIAGRAMS (Continued)
ALE
~ ~ICA
rIDP-H-IPD
EXPANDER ,..----""\.
PORT PCH OUTPUT DATA
OUTPUT
EXPANDER
PORT PCH
INPUT
I
PROG 1......-. _ _
Ipp
_____r-
-1
Figure 10. Port 2 Timing
ICy
I 55 51 52 53
I 54
l 55 51
INPUT
J INST. DECODE EXECUTION INPUT
OUTPUT ADDRESS INC. PC OUTPUT ADDRESS
I I I I I
Figure 11. Instruction Cycle
51 52 53 S4 55 51 52 S3 54 55
CLOCK OUT
ON TO
ALE _1-_-+__-1--'
RD--I---+---I---~--+-.,
WR L-~--4--~
PROG
Figure 12. Instruction Cycle Timing
August 26, 1986 6-57

SCN8049, SCN8050, SCN8039, SCN8040

SCN8049 Series
Table 1 Instruction Set

INSTRUCTION CODE FLAGS
MNEMONIC FUNCTION DESCRIPTION CYCLES BYTES
D-,DsDsD.D3 DID1 DO C AC FO Fl F2
Accumulator
ADD A, # data (A) <- (A) + data Add immadiate the specified data
to the accumulator.
0 0 0 0 0 0 1 1
IIrdsds~dad2d1 do
2 2
··
ADD A, Rr (A)
for
<- (A) + (Rr)
r=0-7
Add contenta of designated
register to the accumulator.
0 1 1 0 1 r r r 1 1
· ·
ADD A, @ Rr (A)
for
<- (A) + «Rr))
r=O-1
Add indirect the contenta the data
memory location to the
accumulator.
0 1 1 0 0 0 0 r 1 1
··
ADDC A, # data (A) <- (A) + (C) + data Add immediate with carry the
specified data to the accumulator.
0 0 0 1 0 0 1 1
d7 de ds d. da d2 d1 do
2 2
· ·
ADDC A, Rr (A) <- (A) + (C) + (Rr)
for r=0-7
Add with carry the oontents of the
designated register to the
accumulator.
0 1 1 1 1 r r r 1 1
· ·
ADDC A, @ Rr (A) <- (A) + (C) + «Rr))
for r=O-1
Add indirect with carry the
oontenta of data memory location
to the accumulator.
0 1 1 1 0 0 0 r 1 1
··
ANL A, # data (A) <- (A) AND data Logical AND specifiad immediate 0 1 0 1 0 0 1 1 2 2
data with accumulator. d7 de ds d. da d2 d1 do
ANL A, Rr (A) <- (A) AND (Rr) Logical AND oontenta of 0 1 0 1 1 r r r 1 1
for r-0-7 designated register with
accumulator.
ANL A, @ Rr (A) <- (A) AND «Rr)) Logical AND indirect the oontents 0 1 0 1 0 0 0 r 1 1
for r=O-1 of data memory with accumulator.
CPL A (A) <- NOT (A) Complement the oontenta of the 0 0 1 1 0 1 1 1 1 1
accumulator.
CLR A (A) <- 0 Clear the oontenta of the 0 0 1 0 0 1 1 1 1 1
accumulator.
DA A
DEC A (A) <- (A)-1

Decimal adjust the oontenta of the
accumulator.
Decrement the accumulator's
0 1 0 1 0 1 1 1
0 0 0 0 0 1 1 1
1
1
1
1
··
contenta by 1.
INC A (A) <- (A) + 1 Increment the accumulato~s 0 0 0 1 0 1 1 1 1 1
oontenta by 1.
ORL A, # data (A) <- (A) OR data Logical OR specified Immadiate 0 1 0 0 0 0 1 1 2 2
data with accumulator. d7 de de d. da d2 d1 do
ORL A, Rr (A) <- (A) OR (Rr) Logical OR oontenta of designated 0 1 0 0 1 r r r 1 1
forr-0-7 register with accumulator.
ORL A, @ Rr (A) <- (A) OR «Rr)) Logical OR indirect the oontenta of 0 1 0 0 0 0 0 r 1 1
for r-O-l data memory location with
accumulator.
RL A (An + 1) <- (An) Rotate accumulator left by l-bR 1 1 1 0 0 1 1 1 1 1
(Ao) <- (A7) withOut carry.
forN-0<-6
RLC A (An + 1) <- (An);
n-0-6
(Ao) <- (C)
Rotate accumulator left by l-bR
through carry.
1 1 1 1 0 1 1 1 1 1
·
(C) <- (A7)
RR A (An) <- (An + 1); Rotate accumulator right by l-bR 0 1 1 1 0 1 1 1 1 1
n-0-6 withOut carry.
(A7) <- (Ao)
RRC A (An) <- (An + 1);
n-0-6
(A7) <- (C)
Rotate accumulator right by I-bit
through carry.
0 1 1 0 0 1 1 1 1 1
·
(C) <- (Ao)
&NAPA (~7) <- (Ao - 3) Swap the 2 4-bit nibbles in the 0 1 0 0 01 1 1 1 1
accumulator.
XRL A, # data (A) <- (A) XOR data Logical XOR specifiad immediate 1 1 0 1 0 0 1 1 2 2
data with accumulator. d7dsde~dad2d1 do
XRL A, Rr (A) <- (A) XOR (Rr) logical XOR Contenta of 1 1 0 1 1 r r r 1 1
for r-0-7 designated register with
accumulator.
XRL A, @ Rr (A) <- (A) XOR «Rr)) Logical XOR indirect the oontenta 1 1 0 1 0 0 0 r 1 1
for r-O-l of date memory location with
accumulator.
August 26, 1986 6-68

SCN8049, SCN8050, SCN8039, SCN8040

SCN8049 Series
Table 1. Instruction Set (Continued)

07 0. Os D. 03 O2 0, Do C AC FO Fl F2
Branch
DJNZ Rr, addr (Rr) +- (Rr)-I; r~0-7 Decrement the specified register 1 1 1 0 1 r r r 2 2
if (Rr) *0: and test contents. 87 a6 8S 84 83 82 81 "0
(PC 0 - 7) +- addr
JBb addr (PC 0-7) <- addr if Jump to specified address if b2b,bol 0 0 1 0 2 2
Bb~ 1 accumulator bit is set. 87 86 85 84 83 82 81 as
(PC) +- (PC) + 2 if Bb
~O
JC addr (PC 0 - 7) +- addr if Jump to specified address if carry 1 1 1 1 0 1 1 0 2 2

C~ 1 flag is set. a7asa5~a3 82 81 as
(PC) <- (PC) + 2 if C ~ 0
JFO addr (PC 0 - 7) +- addr if Jump to specified address if flag 1 0 1 1 0 1 1 0 2 2
FO~ 1 FO is set. 87 86 8 58.483 82 81 "0
(PC) <- (PC) + 2 if
FO~O
JFl addr (PC 0 - 7) +- addr if Jump to specified address if flag 0 1 1 1 0 1 1 0 2 2

Fl ~ 1 Fl is set. 87 as 85 84 83 82 81 ao
(PC) +- (PC) + 2 if
Fl ~ 0
JMP addr (PC 8 -10) .... addr Direct jump to specified address 81089 88 0 0 1 0 0 2 2
8-10 within the 2K address block. 87 as
8S .. "3 82 81 as
(PC 0-7) +- addr 0-7
(PC 11) .... (DBF)
JMPP @ A (PC 0 - 7) .... «A» Jump indirect to specified address 1 0 1 1 0 0 1 1 2 1
within address page.
JNC addr (PC 0 - 7) +- addr if Jump to specified address if carry 1 1 1 0 0 1 1 0 2 2
C~O flag is low. "7as aS . . . . 82 81 as
(PC) .... (PC)+2 if C~1
JNI (PC 0 - 7) +- addr if Jump to specified address if INT 1 0 0 0 0 1 1 0 2 2
iNi=O input is low. a7 as a5 .. "3 a2 ", as
(PC) .... (PC) + 2 if
INT~ 1
JNTO addr (PC 0 - 7) +- addr if Jump to specified address if test 0 0 0 1 0 0 1 1 0 2 2

TO~O is low. a7 as 8S 8.4 a3 82 81 ao
(PC) .... (PC) + 2 if
TO ~ 1
JNTI addr (PC 0-7) .... addr if Jump to specified address if test 1 0 1 0 0 0 1 1 0 2 2
T1 -0 is low. 87 as 8S 14 83 82 81 as
(PC) .... (PC) + 2 if
T1 ~ 1
JNZ addr (PC 0 - 7) .... addr if Jump to specified address if 1 0 0 1 0 1 1 0 2 2
A~O accumulator is non~zero. "7 as os .... 02 0, as
(PC) .... (PC) +2 if A~O
JTF addr (PC 0 - 7) .... oddr if Jump to specified address if timer 0 0 0 1 0 1 1 0 2 2
TF~ 1 flag is set to 1. a7 as as .... a2 a, as
(PC) .... (PC) + 2 if
TF~O
JTO addr (PC 0-7) .... addr if Jump to specified address if test 0 0 0 1 1 0 1 1 0 2 2
TO~ 1 is a 1. 87 as as B4 83 82 81 as
(PC) .... (PC) + 2 if
TO-O
JTl addr (PC 0-7) .... addr if Jump to specified address if test 1 0 1 0 1 0 1 1 0 2 2
Tl ~ 1 is a 1. 87 as 85 B4 83 82 81 as
(PC) .... (PC) + 2 if
Tl =0
JZ addr (PC 0 - 7) .... addr if Jump to specified address if 1 1 0 0 0 1 1 0 2 2
A~O accumulator is O. "7 as as .. a3 a2 a, as
(PC) +- (PC) +2 if A*O
Control
EN I Enable the external (INn intemupt. 0 0 0 0 0 1 0 1 1 1
DIS I
SEL RBO (BS) .... 0
Disable the external (INn interrupt.
Select bank 0 (locations 0 - 7) of
data memory.
0 0 0 1 0
1 1 0 0 0
1 0
1 0
1
1
1
1
1
1 .
August 26, 1986 6-59

Signatics Microprocessor Products Product Specification
SCN8049. SCN8050. SCN8039. SCN8040

SCN8049 Series
Table 1. Instruction Set (Continued)

D-rDeD.D.D3 D2 D, Do C AC FO Fl F2
Control (Cont.)
SEL RBI
SEL MBO
(BS) +- 1
(DBF) +- 0
Select bank 1 (locations 24 - 31)
of data memory.
Select program memory bank 0,
1 1 0 1 0 1 0 1
1 1 1 0 0 1 0 1
1
1
1
1
·
addresses 0 - 2047.
SEL MBI (DBF) +- 1 Select program memory bank I, 1 1 1 1 0 1 0 1 1 1
addresses 2048 - 4095
ENTO CLK Enable clock output on TO pin. 0 1 1 1 0 1 0 1 1 1
Data moves
MOV A, # data (A) +- data Move immediate the specified data 0 0 1 0 0 0 1 1 2 2
MOV A, Rr (A) ...... (Rr); r=0-7

into the accumulator.
Move the contents of the
d7 d6 d5 do da d2 d, do
1 1 1 1 1 r r r , 1
designated register into the
accumulator.
MOV A, @ Rr (A) ...... «Rr)); r=O-1 Move indirect the contents of data 1 1 1 1 0 0 0 r 1 1
memory location into the
accumulator.
MOV A, PSW (A) ...... (PSW) Move contents of the program 1 1 0 0 0 1 1 1 1 1
status word into the accumulator.
MOV Rr, # data (Rr) ...... data; r=0-7 Move immediate the specijied data 1 0 1 1 1 r r r 2 2
into the designated register. d7 d6 d5 d. da d2 d, do
MOV Rr, A (Rr) ...... (A); r=0-7 Move accumulator contents into 1 0 1 0 1 r r r 1 1
the designated register.
MOV @ Rr, A «Rr)) ...... (A); r - 0 - 1 Move indirect accumulator contents 1 0 1 0 0 0 0 r 1 1
into data memory location.
MOV @ Rr, # data «Rr)) +- data; r = 0 - 1 Move indirect the specified data 1 0 1 1 0 0 0 r 2 2
·.· ·
into data memory. d7 de d5 do da d2 d, do
MOV PSW, A (PSW) ...... (A) Move contents of accumulator into 1 1 0 1 0 1 1 1 1 1
the program status word.
MOVP A, @ A (A) ...... «A)) Move data in the current page into 1 0 1 0 0 0 1 1 2 1
the accumulator.
MOVP3 A, @ A (A) ...... «A)) Move data in page 3 into the 1 1 1 0 0 0 1 1 2 1
in page 3 accumulator.
MOVX A, @ Rr (A) +- «Rr)); r=O-1 Move indirect the contents of 1 0 0 0 0 0 0 r 2 1
external memory location into the
accumulator.
MOVX @ Rr, A «Rr)) ...... (A); r=O-1 Move indirect the contents of the 1 0 0 1 0 0 0 r 2 1
accumulator into external memory.
XCH A, Rr (A) " (Rr); r-0-7 Exchange the accumulator and 0 0 1 0 1 r r r 1 1
designated register's contents.
XCH A, @ Rr (A)"«Rr)); r-O-l Exchange indirect contents of 0 0 1 0 0 0 0 r 1 1
accumulator and location in data
memory.
XCHD A, @ Rr (A 0-3)~(Rr)(0-3) Exchange indirect 4·b~ contents of 0 0 1 1 0 0 0 r 1 1
r-O-l accumulator and data memory.
Flags
CPL
CPL
CPL
C
FO
Fl
(C) +- NOT (C)
(FO) ...... NOT (FO)
(Fl) ...... NOT (Fl)
Complement content of carry btt.
Complement content of flag FO.
1
1
0 1
0 0
0
1
0
0
1
1
1
0
1
1
1
1
1
1 · ·.
Complement content of flag Fl. 1 0 1 1 0 1 0 1 1 1
CLR
CLR
C
FO
(C) ...... 0
(FO) +- 0
Clear content of carry bit to O.
Clear content of flag 0 to O.
1
1
0 0
0 0
1
0
0
0
1
1
1
0
1
1
1
1
1
1 · ·
CLR Fl
Input/output
(Fl) ...... 0 Clear content of flag 1 to O. 1 0 1 0 0 1 0 1 1 1
·
ANL BUS, # data (BUS) +- (BUS) AND Logical AND immediate specified 1 0 0 1 1 0 0 0 2 2
data data with BUS. d7 do d5 do da d2 d, do
ANL Pp, # data (Pp) ...... (Pp) AND data Logical AND immediate specified 1 0 0 1 1 0 P P 2 2
p= 1-2 data with deSignated pori (lor 2). d7 de d5 do da d2 d, do
ANLD Pp, A (Pp) +- (PP) AND (A Logical AND contents of 1 0 0 1 1 1 P P 2 1
0-3) accumulator wtth deSignated pori
p=4-7 (4-7).
August 26, 1986 6-60

SCN8049, SCN8050, SCN8039, SCN8040

SCN8049 Series
I
Table 1. Instruction Set (Continued) ~.
D7 D6 D. D. D3 D2 D, Do C AC FO Fl F2
Input/output (Cant.)
IN A, Pp (A) ..... (Pp); p = 1 - 2 Input data from designated port a a a a 1 a p p 2 1
(1 - 2) into accumulator.
INS A, BUS (A) ..... (BUS) Input strobed BUS data into a a a a 1 a a a 1 2
accumulator.
MOVO A, Pp (A 0-3) ..... (Pp); Move contents of designated port a a a 0 1 1 P P 2 1
p=4-7 (4 - 7) into accumulator.
(A4-7) ..... 0
MOVO Pp, A (Pp) ..... A 0-3; p=4-7 Move contents of accumulator to a a 1 1 1 1 P P 1 1
designated port (4 - 7).
OAlO Pp, A (Pp) ..... (Pp) OA (A logical OA contents of 1 a a a 1 1 P P 1 1
0-3) accumulator with designated port
p =4-7 (4-7).
ORl BUS, # data (BUS) .... (BUS) OA data logical OA immediate specified 1 a a a 1 a a a 2 2
data with BUS. d7 ds ds d4 do d2 d, do
OAl Pp, # data (Pp) ..... (Pp) OA data logical OA immediate specified 1 a a a 1 a p p 2 2
P = 1-2 data with designated port (1 - 2). d7 ds ds d4 do d2 d, do
OUTl BUS, A (BUS) ..... (A) Output contents of accumulator 0 a a a a a 1 a 1 2
onto BUS.
OUTl Pp, A (Pp) .... (A); p = 1-2 Output contents of accumulator to 0 a 1 1 1 a p p 1 1
designated port (1 - 2).
Registers
DEC Ar (Ar) ..... (Ar)-l; r=0-7 Decrement contents of designated 1 1 a a 1 r r r 1 1
register by 1.
INC Ar (Ar) ..... (Ar) + 1; r=0-7 Increment contents of designated a a a 1 1 r r r 1 1
register by 1.
INC @ Ar «Ar» ..... «Ar» + 1; Increment indirect the contents of a a a 1 0 a a r 1 1
r=O-l data memory location by 1.
Subroutine
CAll addr «SP» ..... (PC), (PSW Call designated subroutine. a'Oa9 .. 1 a 1 a a 2 2
4-7) 87 as 8S 84 a3 82 81 ao
(SP) ..... (SP) + 1
(PC 6-10) ..... addr
6-10
(PC 0-7) ..... addr 0-7
(PC 11) ..... OBF
AET (SP) ..... (SP) - 1 Return from subroutine without 1 a a a a a 1 1 2 1
(PC) ..... «SP» restoring program status word.
AETR (SP) ..... (SP) - 1 Return from subroutine restoring 1 a a 1 a a 1 1 2 1
(PC) ..... «SP» program status word.
(PSW 4 - 7) ..... «SP»
TimerI counter
EN TCNTI Enable timer/counter interrupt. a a 1 a a 1 a 1 1 1
DIS TCNTI Disable timer/counter interrupt. a a 1 1 a 1 a 1 1 1
MOV A, T (A) ..... (T) Move contents of timer/counter a 1 a a a a 1 a 1 1
into accumulator.
MOV T, A (T) ..... (A) Move contents of accumulator into a 1 1 a a a 1 a 1 1
timer/counter.
STOP TCNT Stop count for event counter or a 1 1 a a 1 a 1 1 1
timer.
STRT CNT Start count for event counter. a 1 a a a 1 0 1 1 1
STRT T Start count for timer. a 1 a 1 a 1 a 1 1 1
Miscellaneous
NOP No operation performed a a a a a a a a 1 1
NOTES:
1. Instruction code designations rand p form the binary representation of the registers and ports involved.
2. The dot under the appropriate flag bit indicates that its content is subject to change by the instruction in which it appears.
3. Numerical subscripts appearing in the FUNCTION column reference the specific bits affected.
August 26, 1986 6-61

SCN8049, SCN8050, SCN8039, SCN8040

SCN8049 Series
SYMBOL DEFINITIONS
SYMBOL DESCRIPTION P "In-Page" operation designator
A The accumulator Pp Port designator (p = 1, 2 or 4 - 7)
AC The auxiliary carry flag PSW Program status word
addr Program memory address (11 bits) Rr Register designator (r = 0, 1 or 0-7)
Bb Bit designator (b = °- 7) SP Stack pointer
BS The bank switch T Timer
C Carry flag TF Timer flag
ClK Clock signal TO, Tl Testable inputs 0, 1
CNT Event counter # Prefix for immediate data
0 Nibble designator (4 bits) @ Prefix for indirect address
DBF
data
Fa, Fl
Program memory bank flip-flop
Number or expression (8 bits)
Flags 0, 1
-....
$ Program counter's current value
Replaced by
Exchanged with
I Interrupt
INT External interrupt
Table 2. Instruction Timing""

CYCLE 1 CYCLE 2
INSTRUCTION 51 52 53 54 55 51 52 53 54 55
IN A,P
Fetch
Instruction
Increment
Program Counter - Increment
Timer - - Read Port
· - - -
OUTL P,A
Fetch
Instruction
Increment
Timer
Output
To Port - - · - - -
ANL P, # data
Fetch
Instruction · Increment
Timer Read Port
Fetch
Immediate Data - · Increment
Program Counter
Output
To Port
-
ORL P, '* data Fetch

Timer Read Port
Fetch
Program Counter
Output
To Port
-
INS A, BUS
Fetch
Instruction
Increment
Program Counter
- Increment
Timer
- - Read Port
· - - -
OUTl BUS, A
Fetch
Instruction
Increment
Timer
Output
To Port
- -
· - - -
ANL BUS, #: data
Fetch
Timer
Read Port
Fetch
Program Counter
Output
To Port -
ORl BUS, # data
Fetch
Program Counter
- Increment
Timer
Read Port
Fetch
Program Counter
Output
To Port
-
MOVX @R,A
Fetch
Instruction
Increment
Program Counter
Output RAM
Address
Increment
Timer
Output
Data to
RAM
- - · - - -
MOVX A,@R
Fetch
Instruction
Increment
program Counter
Output RAM
Address
Increment
Timer
- - Read Data
· - - -
MOVD A, Pi
Fetch
Instruction
Increment
Program Counter
Output
Opcodel Address
Increment
Timer - - Read
P2 lower · - - -
MOVO Pj, A
Fetch
Instruction
Increment
Program Counter
Output
Opcodel Address
Increment
Timer
Output Data
TO P2
Lower
- - · - - -
ANlD P, A
Fetch
Instruction
Increment
Program Counter
Output
Opcodel Address
Increment
Timer
Output
Data
- - · - - -
CRlO P, A Fetch
Instruction
Increment
Program Counter
Output
Opcodel Address
Increment
Timer
Output
Data - - · - - -
J (CONDITIONAL) Fetch
Program Counter
Sample
Condition
Increment
Timer - Fetch
Immediate Data - · Update
Program Counter - -
9TART CNT ISTAT T
Fetch
Program Counter - - Start
Counter
STOP TCNT
Fetch
Program Counter - - Stop
Counter
EN I
Fetch
Program Counter - Enable
Interrupt -
DIS I Fetch
Program Counter - Disable
Interrupt
-
ENTO ClK
NOTES:
Fetch
Program Counter - Enable
Clock -
'Valid instruction address are output at this time if extemal program memory is being accessed,
.. See figures 11 and 12 for instruction cycle and cycle timing,
August 26, 1986 6-62

Signetics Section 7
Sales Offices,
Representatives & I
Microprocessor Products Distributors ,-.

I
Signetics Sales Offices,
Representatives &
Distributors
SIGNETICS NEW JERSEY FLORIDA NEW YORK

HEADQUARTERS Parsippany Clearwater Ithaca
Phone: (201) 334-4405 Sigma Technical Assoc. Bob Dean, Inc.
811 East Arques Avenue Phone: (813) 791-{)271 Phone: (607) 257-1111
P.O. Box 3409 NEW YORK
Sunnyvale, CA 94088-3409 Hauppauge Ft. Lauderdale OHIO
Phone: (516) 348-7877 Sigma Technical Assoc. Centerville
Phone: (408) 991-2000 Phone: (305) 731-5995 Bear Marketini;' Inc.
Wa~pingera Falla Phone: (513) 36-2061
ALABAMA hone:(914) 297-4074 ILLINOIS
Huntsville Hoffman Estates Richfield
Phone: (205) 830-4001 NORTH CAROLINA Bear Marketing, Inc.
Raleigh Micro-Tex, Inc.
Phone: (312) 382...,'3001 Phone: (216) 659...,'3131
ARIZONA Phone: (919) 781-1900
Phoenix OKLAHOMA
OHIO INDIANA Tulsa
Phone: (602) 968-5777 Indianapolis
Columbus Jerry Robison
CALIFORNIA Phone: (614) 888-7143 Mohrfield Marketing, Inc. and Associates
Calabasas Phone: (317) 54EH;969 Phone: (918) 665-3562
Da~ton
Phone: (818) 880-6304 hone: (513) 294-7340 IOWA OREGON
Irvine OREGON Cedar Rapids Beaverton
Phone: (714) 833--8980 Beaverton J.R. Sales Western Technical Sales
(714) 752-2780 Phone: (503) 627-{)110 Phone: (319) 393-2232 Phone: (503) 644-8860
Los Angeles PENNSYLVANIA MARYLAND PENNSYLVANIA
Phone: (213) 670-1101 Plymouth Meeting Columbia Pittsbur~h
Phone: (215) 825-4404 Third Wave Solutions, Inc. Bear arketing, Inc.
San Diego Phone: (301) 290-5990 Phone: (412) 531-2002
Phone: (619) 56Q-{)242 TENNESSEE
Greeneville MASSACHUSETTS Hatboro
Sunnyvale Delta Technical
Phone: (408) 991...,'3737 Phone: (615) 639-{)251 Needham Heights
Kanan Associates Sales, Inc.
COLORADO TEXAS Phone: (617) 449-7400 Phone: (215) 975-{)600
Aurora Austin
Phone: (512) 339-9944 MICHIGAN UTAH
Phone: (303) 751-5011 Salt Lake City
Bloomfield Hills
Houston Enco Marketing Electrodyne
FLORIDA Phone: (713)668-1989 Phone: (801) 264-8050
Ft. Lauderdale Phone: (313) 338-8600
Phone: (305) 48EH;300 Richardson WASHINGTON
Phone: (214) 644...,'3500 MINNESOTA Bellevue
GEORGIA Eden Prairie Western Technical Sales
Atlanta CANADA High Technolo," Sales Phone: (206) 641-3900
Phone: (404) 594-1392 SIGNETICS CANADA, Phone: (612)9 4-7274
LTD. Spokane
ILLINOIS Etobicoke, Ontario
MISSOURI Western Technical Sales
Itasca Bridgeton Phone: (509)922-7600
Phone:(416)626-6676
Phone: (312) 25Q-{)050 Centech, Inc.
Ne~ean, Ontario Phone: (314) 291-4230 WISCONSIN
INDIANA hone: (613) 225-5467 Waukesha
Kokomo Raytown Micro-Tex, Inc.
Phone: (317) 459-5355 Centech, Inc. Phone: (414) 542-5352
REPRESENTATIVES Phone: (816) 358-8100
KANSAS CANADA
Overland Park ARIZONA NEW HAMPSHIRE Burnaby, B.C.
Phone: (913) 469-4005 Scottsdale Hookset Tech-Trek, Ltd.
Thorn Luke Sales, Inc. Kanan Associates Phone: (604) 439-1373
MASSACHUSETTS Phone: (602)941-1901 Phone: (603) 645-{)209
Westford Misslssauga, Ontario
Phone: (508) 692-6211 CALIFORNIA NEW JERSEY Tech-Trek, Ltd.
Orangevale East Hanover Phone: (416) 238-{)366
MICHIGAN Webster Associates Emtec Sales, Inc. Ne~ean, Ontario
Farmington Hills Phone: (916) 989-{)843 Phone: (201) 428-{)600 ech-Trek, Ltd.
Phone: (313) 553-6070 Phone: (613) 225-5161
CONNECTICUT NEW MEXICO
MINNESOTA Fairfield Albu~uerque Ville SI. Laurent, Quebec
Edina NRG, Limited F.. Sales Tech-Trek, Ltd.
Phone: (612)835-7455 Phone: (203) 384-1112 Phone: (505) 345-5553 Phone: (514) 337-7540
April 1989 7...,'3

Signetics
Sales Offices, Representatives & Distributors
DISTRIBUTORS DENMARK Philips Components Japan SOUTH AFRICA

Philips Components AIS Tokyo SA Philigs (PTY), Ltd.
Contact one of our Copenhagen S Phone: 81-3-280-2620 Rand urg
local distributors: Phone: 45-1-54-11-33 Phone: 27-11-889-3911
Anthem Electronics KOREA
Avnet Electronics FINLAND Philips Industries, Ltd. SPAIN
OyPhilipsAb Seoul Co~resa S.A.
Aztech Electronics Espoo Phone: 82-2-794-5011 arcelona
Hamilton/Avnet Electronics Phone: 358-0-502-61 1213/4/5
Marshall Industries Phone:34-3-301-63-12
Schweber Electronics FRANCE MALAYSIA
R.T.C. Compelec SWEDEN
Wyle/LEMG Philips Malaysia SON Philips Components A.B.
Issy-ies-Moulineaux Bernhsd
Zentronics, Ltd. Cedex Stockholm
Pulau Penang Phone: 46-8--782-10-00
Phone: 33-1-40-93-80-00 Phone: 60-4-870-055
FOR SIGNETICS
GERMANY SWITZERLAND
PRODUCTS Valvo MEXICO Philips Components A.G.
WORLDWIDE: Hamburg Panamtek Zuerich
Phone: 49-40-3-296-0 Guadalajara. Jal Phone:41-1-488-2211
ARGENTINA Phone: 52-36-30-30-29
Philips Argentina S.A. GREECE
Buenos Aires TAIWAN
Philips S.A. Hellenique Mexico. D.F. Philips Taiwan, Ltd.
Phone: 54-1-541-7141 Athens Phone: 52-5-586-84-43 Taipei
AUSTRALIA Phone: 30-1-4894-339 Phone: 886-2-712-0500
Philips Electronic NETHERLANDS
HONG KONG Philips Nederland
Components & Mat'I Ltd. Philips Hong Kong, Ltd. Eindhoven THAILAND
Artarmon. N.SW. Kwai Chung. Kowloon Phone: 31-40-444-755 Philips Electrical Co.
Phone: 61-2-439-3322 Phone: 852-0-245-121 of Thailand Ltd.
NEW ZEALAND Bangkok
AUSTRIA INDIA Phone: 66-2-223-6330/9
Osterrichische Philips Peico Electronics Philips N_ Zealand Ltd.
Wien & Elect. Ltd. Auckland
Phone: 64-9-605-914 TURKEY
Phone: 43-222-60-1 01 Bombay Turk Philips
-820 Phone: 91-22-493-0311 Ticaret A.S.
NORWAY
BELGIUM INDONESIA Norsk AlS Philips Istanbul
S.A. MBLE Components P.T. Phlllcs-Raiin Oslo Phone: 90-1-179-27-70
Brussels Electron cs Phone: 47-2-68-02-00
Phone: 32-2-525-61-11 Jakarta Selatan UNITED KINGDOM
Phone: 62-21-512-572 PERU Philips Components
BRAZIL Cadesa London
Philips Do Brasil, Ltda. IRELAND San Isidro Phone: 44-1-580-6633
Sao Paulo Philips Electrical Ltd. Phone: 51-14-707-080
Phone: 55-11-211-2600 Dublin UNITED STATES
CHILE Phone: 353-1-69-33-55 PHILIPPINES Signetics International
Philips Chilena S.A. ISRAEL Philips Industrial Dev., Inc. co~.
Santiago Makati Metro Manila unnyvale, California
Ra~ac Electronics, Ltd. Phone: 63-2-810-01-61 Phone: (408) 991-2000
Phone: 56-02-077-3816 elAviv
CHINA, Phone: 972-3-477115 PORTUGAL URUGUAY
PEOPLES REPUBLIC OF ITALY Philips Portuguesa SA Luzllectron SA
Philips Hong Kong, Ltd. Philips S.p.A. Lisbon Montevideo
Kwai Chung, Kowloon Milano Phone:351-1-68-31-21 Phone: 598-91-56-411
Phone: 852-0-424-5121 Phone: 38-2-67-52-1' 42/43/44
SINGAPORE
COLUMBIA JAPAN Philips Project Dev. VENEZUELA
Iprelenso, Ltda. Philips Components Japan Pte., Ltd. Magnetica S.A.
Bogota Osaka-Shi Singapore aracas
Phone: 57-1-2497624 Phone: 81-6-389-7722 Phone: 65-350-2000 Phone: 58-2-241-7509
April 1989 7-4

S83C552/S80C552 SC87C451 SC80C4511SC83C451 SCN8032AH/SCN8052AH
INDEX -- ~
64 ALE
~
:~
EAIVPP 1 64 AlE/PFiOG T2JP1.0~ 40 Vee
"~'t:l
~ PO.O/ADO
~PS""EN
P2.0/A8 2 P2.0/A 63 PSEN T2EX/Pl.1 ~
P2.1/A9 3 t¥ P6.7 P2.l/A 9 3
P2.2/Al o 4 ~
61
P6.?
P6.6
Pl.2 3
P1.3 4
38 PO.l/AD1
37 PO.2/AD2
P2.2/Al0~ 61 P6.6
PLCC P2.3/Al 36 PO.3/AD3
P2.3/All ~ 60 P6.5
P2.4/Al
'F1, 60 P6.5 P1.4 5
35 PO.4/AD4
~ff
59 P6.4 P1.5 6
:~::;~~!~
26 44 59 P6.4
58 P6.3 P2.5/Al 58 P6.3 P1.6~ 34 PO. 51 ADS
27 43 P2.6/Al 4 8 P6.2 ~
~ :~~~
P2.6/Al4 8 PO.6/AD6
TOP VIEW ~ P6.2
~~
P2.7/Al 56 P6.1 32 PO.7/AD7
:~..;::~~~
56 P6.1 -
Pin Function PI, Function PO.7/AD 55 P6.0 RxD/P3.0 10 DIP 31 EA
55 P6.0
1 P5.0/ADCO 35 XTALl PO.6/AD61fi 54 AfLAG TxD/P3.1 11 30 ALE
:~::;~~:~
2 VoD 36 V" 54 AFLAG
PO.5/AD 512 BFLAG
~I DS
3 STADG 37 V" 53 BFLAG INTO/P3.2 12 29 PSEN
4 PwMo 38 NC PO.4/AD 413 28 P2.7/A15
5 PWMT 39 P2.0/A08 PO.4/AD413
~iOs ODs
INT1/P3.3~
~~
6 f"W 40 P2.1/A09 PO.3/AD3 14 PO.3/AD 51 TO/P3.4 14 ~ P2.6/A14
51 ODS
,
7 P4,O/CMSr~O 41
P4.1/CMSfll 42
P2.2/Al0
P2.3/Al1 PO.2/AD2~ 50 Vss
PO.2/AD
POol/AD 1 16
50 V"
XTALl
T1/P3.5 15 26 P2.5/A13
~
9 P4,?/CM:;f12 43 P2.4/A12 WR/P3.6 16 25 P2.4/A12
:~:~;~~~~
49 XTALl
10
11
r4.:1/CM:;\\J 44
P4,4fCM::!!4 45
P2.S/A13
P2.6/A14 DIP
48 XTAL2 PO.O/AD 017
Ye e 18
DIP 4'47 PS.7
XTAL2 RoJP3.7 17 24 P2.3/Al1
23 P2.2/Al0
12 1'4 !)/C:M~;H5 46 P2.71A1S Vee 18 47 P5.7 XTAL2~
PSEN P4. 46 P5.6
13
14
f'4 n/c'Mll1
i'4.fICMll
H~; !
47
4'
49
ALE
i'A
P4.319
P4.2 20
46 PS.6
45 P5.5
P4. !¥o 45 PS.5
XTAL1 ~
Vss 20
22 P2.1/A9
21 P2.0/A8
"
16
17
PI (J!C1UI
1'1, lie1 II
50
51
PO.7/AD?
PO.S/ADS
P4.1 21 ~ P5.4
P4. 121
P4. 022
44 P5.4
43 PS.3
TOP VIEW
1A l'I.:.'IC1;>1 52 PO.5/AD5 P4.0 22 43 P5.3 INDEX
1,1 1'1,:l/C1:11 63 PC.4/AD4 Pl.0 23 42 PS.2 P1. 023 42 P5.2 CORNER 6 1 40
EJ
PO.3/AD3
"
21
1'1,4/1;>
Pl.f)/fH2
54
55 PO.2/AD2
Pl.! 24
P1.225
41 P5.1 P1.
P1. ~¥S
41 P5.1
40 PS.O
~ :::~/Ro
22 pl.S/sel 56 PO.1/AD'
P1.71SDA 57 PO.D/ADO P1. 326
~
23 P1.326 P3.7IRo PlCC
24 P3.0/RXO 66 AVref-
P1. 427 36 P3.6/WR
:~::~
25 P3.1/TXD 59 AVref+ 38 P3.6/WR
26 P3.2/INTO 60 AVSS P1. 528 37 P3.5/T1 17 29
37 P3.5/T1
27 P3.3/TN'i'T 61 AVOD
~¥o
Pl.629 P1. 36 P3.4/TO
~ :::;;~:T1
28 P3.4/TO 62 P5.7/AOC7 18 28
29 P3.5/Tl 63 P5.6/ADC6 Pl.7 30 P1. 35 P3.3/TNfi TOP VIEW
30 P3.6/~ 64 P5.5/ADC5 RS T31
~
P3.2/1NTo
P3.0/::~~
31 P3.7iRD 65 P5.4/ADC4 34 P3.2/"'iNTO Pin Function Pin Function
32 NC 66 P5.3/ADC3 33 P3.1/TxD P3.0/RxD 32 33 P3.l/TxD 1 NC 23 NC
33 NC 67 PS.2/ADC2 2 T2/Pl.0 24 P2.0/A8
34 XTAl2 P5.1/ADCl TOP VIEW TOP VIEW 3 T2EX/Pl.1 25 P2.1/A9
6'
4 Pl.2 26 P2.2/Al0
INDEX INDEX 5 P1.3 27 P2.3/Al1
CORNER 9 1 61
"~d
S83C652/S80C652 Pl.4 P2.4/A12
'8'
6 28
7 P1.5 29 P2.5/A13
10 0 60 8 P1.6 30 P2.6/A14
PI,O 1 40 Vee 9 P1.7 31 P2.7/A1S
PI,1 2 39 PO.D/ADO LCC LCC 10 RST 32 rsEN
11 RxD/P3.0 33 ALE
I'l" 3 38PO.l/AOl 12 NC 34 NC
1'1 :1 4 37 PO.2/A02 26 44 26 44 13 TxD/P3.1 35 EA
14 rFrrO"/P3.2 36 PO.7/AD7
1'1 4 5 36 PO.3/A03 27 43 27 43 15 mTi/P3.3 37 PO.6/AD6
I' 1 .~, (} 35 PO.4/AD4 TOP VIEW TOP VIEW 16 TO/P3.4 36 PO.5/AD5
17 Tl/P3.5 39 PO.4/AD4
:;CI./I'1.6 I 34 PO.5/AD5 Pin Function Pin Function Pin Function PI, Function Pin Function Pin Function V'i7!=l/P3.6 40 PO.3/AD3
18
~PO.6/AD6 Ri5/P3.7 PO.2/AD2
SDAfrl:~~~ 1 EAJVPP 24 P4.2 47 PS.3 1 i'A 24 P4.2 47 P5.3 19 41
2 P2.0/A8 25 P4.l 48 2 P2.0/A8 25 P4.1 48 20 XTAL2 42 PO.1/AD1
¥.~.7/AD7 PS.4 P5.4
3 P2.1/A9 26 P4.0 49 P5.5 3 P2.1/A9 26 P4.0 49 P5.S
RxD/DA1A/P:1.O 10
TxD/ClOCK/P3.1 11
DIP 31 EA
30ALE
4
5
P2.2/Al0
P2.3/All
27
28
Pl.0
Pl.1
50
51
P5.6
P5.7
,
4 P2.2/Al0
P2.3/A11
27
28
Pl.0
Pl.1
50
51
P5.6
P5.7
22 V" 44 Vee
6 P2.4/AI2 29 Pl.2 52 XTAl2 6 P2.4/A12 29 Pl.2 52 XTAL2

29 PSEN
IN-rOIP3.2 12 7 P2.5/A13 30 Pl.3 53 XTAL1 ,
7 P2.5/A13 30 Pl.3 63 XTALl
IN~~;:::! H
28 P2.7/A1S 8 P2.6/A14 31 Pl.4 54 V" P2.6/A14 31 P1.4 54 V"
gP2.6/A14 9 P2.7/A15 32 P1.S 55 ODS 9 P2.7/A15 32 P1.5 55 ODs
26 P2.5/A13
10 PO.7/AD7 33 Pl.6 56 iDS 10 PO.7/AD7 33 Pl.6 56 iDS
Tl/P3.515 11 PO.6/AD6 34 Pl.? 67 BFLAG 11 PO.6/AD6 34 Pt.7 57 BFLAG
WR/P3.616 25 P2.4/A12 12 PO.5/ADS 35 RST 58 AFLAG 12 PO.5/AD5 35 RST 66 AFLAG
RD/P3.7 H ~P2.3/A11
13
14
PO.4/AD4
PO.3/AD3
36
37
P3.0/RxD 59
P3.l/TxD 60
P6.0
P6.1
13
14
POA/AD4
PO.3/AD3
36
37
P3.0/RxD 59
P3.1/!21L 60
P6.0
P6.1
XTAl218 gP2.2/Al0 15 PO.2/AD2 38 P3.2/ii\l'i'O 61 P6.2 15 PO.2/AD2 38 P3.21ltllQ 61 P6.2
16 PO.l/AD1 39 P3.3/INTl 62 P6.3 16 PO.I/AD1 39 P3.3/1NTl 62 P6.3
XTALl 19 22 P2.l/A9
17 PO.O/ADO 40 P3.4/TO 63 P6.4 17 PO.D/ADO 40 P3.4/TO 63 P6.4
Vss 20 21 P2.0/A8 18 16 Vee 41 P3.5/Tl 64
~~:~~W
Vee 41 64 P6.5 P6.5
19 P4.7 42 65 P6.6 19 P4.7 42 P3.6/!tZB 65 P6.6
'ToPViEW 20 43 20 P4.6 43 P3.7/RD
~~JN
P4.6 P3.7/RD 66 66
INDEX 21 P4.5 44 PS.O 67 ~~'~N 21 P4.5 44 P5.0 67
CORNER 6 1 40 22 P4.4 45 PS.1 68 ALE/Pi"fc5G 22 P4.4 45 P5.l 66 ALE
23 P4.3 46 P5.? 23 P4.3 46 P5.2
Pin Function
EJ
1f
"
PlCC
TOP VIEW
Pin
"
29
Function
1 NC 23 NC
2 PLO 24 P2.0/A8
3 PI.1 25 P2.1/A9
4 P1.2 26 P2.2/Al0
5 PI.3 27 P2.3/Al1
P1A P2.4/A12
6
7
8
Pl.!>
SCLlI'l.t;
"
29
30
P2.5/A13
P2.6/A14
9 SDA/f'l.1 31 P2.7/A1S
10 RST 32 rnN
11 RxD/DA 1 A/P3.0 33 ALE
12 NC 34 NC
13 Tx[)IICII)CK/P3.1 35 ~
14 TNTr\/I':l;.1 36 PO.7/AD7
15 mTill'.1 I 37 PO.6/AD6
16 10!f':1·' 38 PO.5/AD5
17 11/I'::!.!; 39 PO.4/AD4
16 ~/P:1.r, 40 PO.3/AD3
19 1'10/P3.7 41 PO.2/AD2
20 XTAI.;> 42 PO.l/AD1
21 XTAl.l PO.D/ADO
Vco
22 V"
"
Signetics
Signetics Company
81 1 E. Arq ues Avenue
P. O. Box 3409
Sunnyvale, Cali forn ia 94088-3409
Telephone 4081991-2000
98 -8000 -000 O Copyright 1989 NAPC Printed in U.SA. 9167M fGT Ef70Mf FPf0589
Signetics
Philips Components _
e PHILIPS
PHILIPS

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INTEGRATED CIRCUITS

Signetics registers eligible circuits under

© Copyright 1989 Signetics Company

All rights reserved.

Section 1 - 8051 Family

Section 2 - 8051 Family Derivatives

Section 3 - Application Notes

Section 4 -Inter-Integrated (FC) Circuit Bus

Section 5 - Development Support Tools

Section 6 - Additional Microcontroller Data Sheets

Section 7 - Sales Offices, Representatives & Distributors ................................................. 7-3

Port Structures and Operation ................................... 1-22

The Signetics 8051 family of products is based on the 8OC5lBH

Table 1. 8051 Family of Microcontrollers

February 1989 1-1

Section 1 8051 Family Overview

83C552 • 19 I/O lines

83C652 The 83C752 is a derivative version of the 80C51 that is

Table 2. 80C51 Derivative Comparisons

February 1989 1-3

Section 1 8051 Family Architecture

8051 ARCHITECTURE 8051 FAMILY DEVICES

February 1989 1-4

Section 1 8051 Family Architecture

Figure 2. 8051 Block Diagram

Figure 3. 8051 Memory Structure

February 1989 1-5

Section 1 8051 Family Architecture

In the 8051, if the EA pin is strapped to Vcc, then the

The hardware configuration for external program execu-

DATA MEMORY Figure 5. Executing from External

Two-byte addresses can also be used, in which case the

February 1989 1-6

Section 1 8051 Family Architecture

rrH ·--------r----, rrH

Internal Data Memory addresses are always one byte

The Lower 128 bytes of RAM are present in all 8051

All of the bytes in the Lower 128 can be accessed by BOH

either direct or indirect addressing. The Upper 128 -PORT PINS

OH or 8H. The bit addresses in this area are 80H

February 1989 1-7

Section 1 8051 Family Architecture

8051 FAMILY INSTRUCTION SET ADDRESSING MODES

PROGRAM STATUS WORD INDIRECT ADDRESSING

Figure 11. PSW (program Status Word) Register in 8051 Devices

February 1989 1-8

Section 1 8051 Family Architecture

IMMEDIATE CONSTANTS ARITHMETIC INSTRUCTIONS

Table 3. 8051 Arithmetic Instructions

Addressing Modes Execution

February 1989 1-9

Section 1 8051 Family Architecture

The MUL AB instruction multiplies the Accumulator by ANL A, <byte>

Table 4. 8051 Logical Instructions

Mnemonic Addressing Modes Execution

February 1989 1-10

Section 1 8051 Family Architecture

Addressing Modes Execution

February 1989 1-11