Lab PLC

LabPLC
User’s manual for LabPLC software
Projected and designed by Mirko Bjelica (mikanb@Eunet.yu)

May 2000.
I would like to express very special gratitude to Mr.
Mark C. Alberts who sponsored me with the BASCOM-8051
software and helped me to create LabPLC, my final work at
Polytechnic Engineering College.
Short introduction to PLCs
(Originally taken from Panayiotis Stassinopoulos)
A typical industrial automation system, consist of three discrete

parts:
Inputs, which represent the senses of the system and has to do with
the facts that are taking place at the environment of the application. Those
inputs could be pressure sensors, temperature sensors, velocity sensors,
approach sensors, buttons, switches etc.
Outputs, with which the system affects its environment, such as
relays, actuators etc.
Control unit, which is the brain of the entire automation system.
The operation of the system is realized with a combination of the above
three parts. The data flow from the inputs through the control unit, in
which they are processed, to the outputs.
Once, a control unit was consisted of analog circuits or digital
circuits who made an excessive usage of logic components or relays. Last
years, with the great development of computer science many
microcomputer-based systems have started to come on the foreground.
The most popular device that was designed is the PLC (Programmable
Logic Controller). A PLC is a complete computer system, specialized for
use with automation systems. It contains a microprocessor, ROM, RAM
for storing its program and a battery to protect its data due to a low
voltage condition.
The inputs and outputs of the application are connected on the
PLC. First implemented PLCs, were supporting control only on digital
signals, so inputs and outputs should be in digital format. Later, there
were designed PLCs which could control analog signals through analog
inputs and outputs.
Programming PLCs
In order to realize the required automation, a PLC should first be

programmed. There have been developed three PLC programming
languages.
STL: It is the most popular and powerful language. It consists of
instructions' list.
For example:
L I3
O T1
= M1
L I2
...
LAD: It's a graphical programming language which looks like the
auxiliary circuit of a relay-based system.
For example:
CSF: It is also a graphical programming language which is the same

with the circuit of the automation made of logic gates.
For example:
Although the basic programming instructions are the same, their

usage may differ from one PLC to another, depending on its model and
manufacturer. Modern PLC’s offer advanced programming techniques,
including program blocks, subroutines and functions which can be
accessed from different points of the main program.
In order to import a program in a PLC we must use a special device
called Programmer, or a PC that “runs” the appropriate software.
Once a program is stored in the PLC’s memory, it starts executing
cyclically. By saying this we mean that after the execution of the last
instruction of the program, PLC’s controller goes back to the beginning
of the program and executes it again. Acting this way there is a
continuous scanning and processing of the inputs (polling method).
LabPLC Software
For the proper work of PLC device it’s necessary to put in his
memory a program on which it will work. It can be accomplished in
several ways, and one, that I used, is to use personal computer for
downloading program into PLC. This is of course possible if PC has
installed proper software and in further reading I will explain how to use
software that I made. Application is created using programming language
Visual Basic 1.0 for DOS. It’s been realized to maximally simplify
functions entering by only selecting them and not entering logic
functions, inputs, outputs or memory markers by writing names from
keyboard. Next table shows codes of logic functions, inputs, outputs and
memory markers. Of course, this codes are completely useless for user,
but they could be useful for future upgrades or if someone would wish to
make other versions of this software (Windows version for example).
NAME CODE NAME CODE

AND 10 OUTPUT 3 22
OR 11 OUTPUT 4 23
NOT 12 MARKER 0 30
NAND 13 MARKER 1 31
NOR 14 MARKER 2 32
EXOR 15 MARKER 3 33
TIMER 24 MARKER 4 34
INPUT 1 16 MARKER 5 35
OUTPUT 1 20 MARKER 9 39
OUTPUT 2 21 END CODE 99
Table 1. Codes
Software starts when user changes path into directory where

LabPLC files are copied and types into command line “labplc.exe”. The
path could be C:\LABPLC\labplc.exe. After this action, start screen will
show.
Picture 1. Start Screen
After starting the program, user should select proper

communication port (COM Port) for correct connecting with LabPLC.
Default setting is for COM1. Selection is made from “Port” menu.
Picture 2. COM Port selection
In order to consider program working and explaining the function

of some elements from start menu it can be split into three parts. Part for
logic elements and their inputs and outputs selection, which consists of
four combo box controls, keypad and window for showing entered
functions.
Picture 3. Combo Box controls for logic function selection and one of inputs
If Timer function is selected, list box will appear instead of combo

box for second input selection and in this list box user can select preset
time for timer in range from 1 to 99 seconds. When timer gets high logic
level on his input, timer will set output to high level and this level will
hold for preset time.
Picture 4. Timer properties
After first selection is made, it is necessary to interpret (Compile)

logic function or timer into code that microcontroller would
”understand”. This action could be achieved by activating “(Compile)”
key, which is located on the keypad or selecting this function from
“Command” menu. After activation of this option, entered logic function
is shown in “Entered functions” window and pointer is incremented.
Picture 5. Part of the screen, which indicates entered functions and keypad
Besides “Port” falling menu, there is two more menus,

“Commands” menu and “File” menu. In menu “File” there are four
standard options: New, Load, Save As and Exit. Selecting first option,
completely new input will be started and all previous functions will be
erased. “Load” and “Save As” options are used for file manipulations. It
is often in other programs that File menu has these two options. Option
“Exit” is used to exit program.
Picture 6. “File” menu
Menu “Commands” consists of five options with theirs shortcuts

and these options also could be found on keypad. It should be mentioned
that “Compile” isn’t real compile (There is no compiler software), it is
more like interpreter but in this program word compile is more
appropriate for use. Next picture shows this menu.
Picture 7. “Commands” menu
FUNCTION SHORTCUT
NEW Ctrl+N
LOAD F3
SAVE F2
EXIT Ctrl+X
COMPILE F7
NEXT F6
PREVIOUS F5
TRANSFER F9
DELETE F8
Table2. Shortcut codes
HOW TO HANDLE LabPLC
It is very easy to use LabPLC. When you turn on switch PR1 you
are connecting 24V power supply to PLC and LED L1 (POWER ON)
goes on. I used 24V because it is a standard for industrial voltage levels
for supply and for control signals. At the same time LED L2 starts to
blink and that signifies that PLC is READY for data transmission.
Transmission between PC and PLC goes with a speed of 4800 bits per
second with 8 data bits, none parity and 1 stop bit. When transfer ends,
L2 goes off and L11 (READY) starts to shine. From that moment PLC
starts cyclical program execution. Changing logic states on inputs would
directly affect logic states on outputs and it’s controlled by the logic,
implemented true program.
EXAMPLES
When I finished construction of PLC I decided to make few

examples of electro-motor drive in order to show its use. First example
illustrates how to start electro-motor using the PLC. Next example shows
changing direction of shaft rotation and finally, the last example
demonstrates starting of three phase electro-motor in star-delta mode.
Example1:
MARKER 0
INPUT 1
START
K1
OUT 1
INPUT 2
STOP
MARKER 1
Example1. Electro-motor starting
Example1-1. Program window of entered functions

Example2:
MARKER0
MARKER3
INPUT 1
LEFT OUT1
K1
`
MARKER5
INPUT 2 MARKER1
RIGHT
MARKER6
OUT2
INPUT 3 K2
STOP
MARKER2 MARKER4
Example2. Changing direction of shaft rotation

Example3:
OUT1
K1
INPUT 1 MARKER0
STOP
OUT2
K2
INPUT 2
START
MARKER1 MARKER3
OUT3
MARKER2 K3
Example3. Starting 3 phase electro-motor in star-delta mode

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LabPLC

User’s manual for LabPLC software

Projected and designed by Mirko Bjelica (mikanb@Eunet.yu)

A typical industrial automation system, consist of three discrete

In order to realize the required automation, a PLC should first be

CSF: It is also a graphical programming language which is the same

Although the basic programming instructions are the same, their

NAME CODE NAME CODE

Software starts when user changes path into directory where

After starting the program, user should select proper

Picture 2. COM Port selection

In order to consider program working and explaining the function

If Timer function is selected, list box will appear instead of combo

Picture 4. Timer properties

After first selection is made, it is necessary to interpret (Compile)

Besides “Port” falling menu, there is two more menus,

Picture 6. “File” menu

Menu “Commands” consists of five options with theirs shortcuts

HOW TO HANDLE LabPLC

When I finished construction of PLC I decided to make few

Example1. Electro-motor starting

Example1-1. Program window of entered functions

Example2. Changing direction of shaft rotation

Example2-2. Program window of entered functions

Example3. Starting 3 phase electro-motor in star-delta mode

Example3-3. Program window of entered functions

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