This document summarizes key concepts in electronic logic circuits. It discusses how logic circuits use binary representations of 1s and 0s and how their inputs and outputs can only take two states. The core components of logic circuits are logic gates that perform functions like AND and OR. Common logic gates are constructed from integrated circuits using technologies like TTL and CMOS. Logic circuits are used to build components like adders, subtractors, clocks, latches, flip-flops and counters that have important functions in digital electronics and computing.
This document summarizes key concepts in electronic logic circuits. It discusses how logic circuits use binary representations of 1s and 0s and how their inputs and outputs can only take two states. The core components of logic circuits are logic gates that perform functions like AND and OR. Common logic gates are constructed from integrated circuits using technologies like TTL and CMOS. Logic circuits are used to build components like adders, subtractors, clocks, latches, flip-flops and counters that have important functions in digital electronics and computing.
This document summarizes key concepts in electronic logic circuits. It discusses how logic circuits use binary representations of 1s and 0s and how their inputs and outputs can only take two states. The core components of logic circuits are logic gates that perform functions like AND and OR. Common logic gates are constructed from integrated circuits using technologies like TTL and CMOS. Logic circuits are used to build components like adders, subtractors, clocks, latches, flip-flops and counters that have important functions in digital electronics and computing.
This document summarizes key concepts in electronic logic circuits. It discusses how logic circuits use binary representations of 1s and 0s and how their inputs and outputs can only take two states. The core components of logic circuits are logic gates that perform functions like AND and OR. Common logic gates are constructed from integrated circuits using technologies like TTL and CMOS. Logic circuits are used to build components like adders, subtractors, clocks, latches, flip-flops and counters that have important functions in digital electronics and computing.
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The term logic in electronics refers to the
representation and logical manipulation of
numbers usually in a code employing two symbols. i.e., bits.
An electronic logic circuit is one whose inputs and outputs can take only one of two states. Where the output of such a circuit depends only on the present state of the input to the circuit, it is called a combinational logic circuit. (Other case is sequential logic circuit)
Logic circuits may have many inputs and many outputs and be made up of a large number of elements called logic gates Most modern electronic logic networks are constructed from two state components in the form of integrated circuits (IC) fabricated in a single piece of pure silicon and often referred to as a CHIP.
They are available as transistor-transistor logic (TTL) and complementary symmetry metal oxide semiconductor (CMOS) which supersede earlier resistor-transistor logic (RTL) and diode-transistor logic (DTL). A logic gate is an electronic device that has a single output terminal and a number of inputs, or control terminals.
If voltage levels representing the binary states of 1 or 0 are fed to the input terminals, the output terminal will adopt a voltage level equivalent to 1 or 0, depending upon the particular function of the gate.
The basic logic gates provide the functions of AND and OR.
Circuit Symbol Truth Table
Equivalent circuit Truth Table Equivalent circuit Truth Table Equivalent circuit Truth Table Equivalent circuit Truth Table "A room has two doors and a central light, and switches are to be fitted at each door such that either switch will turn the light on and off". Equivalent circuit Truth Table A B = AB + AB Either the NAND or the NOR gate can be connected to operate as a simple inverter as illustrated in the following figure.
In diagram (a) a 2 input NAND gate is shown with one input permanently held at the 1 state (+ 5v), and the resulting output will be the inversion of the single input A.
Diagram (b) shows a 2 input NOR gate with one input permanently held at the 0 state (0v) again resulting in an output which will be the inversion of the single input A. (a) NAND INVERTER (b) NOR INVERTER A A +5V OV A A Another instance where multiple inputs to a single gate operation can occur is with certain types of gate elements that have an 'EXTENDED INPUT' facility provided.
The circuit illustrated in the figure is a typical example, showing a 3 input NAND gate (element X).
A connection from the base of the transistor is brought out in order that further inputs (element Y) can be connected to extend the input range (i.e. inputs D and E) Delay elements are used to 'delay' the travel of a pulse along a line for a short period of time.
This is occasionally necessary to ensure that one bit of information does not arrive at some point in the circuit earlier than another.
Most delay times are relatively small and only amount to few mili-seconds. Occasionally it is required to 'hold' one input to an AND gate at a particular logic level in order to disable the entire gate.
One method of representing this symbolically is shown in figure which illustrates a two input gate with an 'INHIBIT' input C carrying an active state indicator.
In this case, with a 1 state at the inhibit input C, the gate is disabled irrespective of the input conditions at A and B.
With a 0 state at the inhibit input C, however, the gate is 'enabled' and the output will adopt the 1 state when both input A and input B are at the 1 state. 1. Adders 2. Subtractors 3. Clocks 4. Latches 5. Flip-flops 6. Counters
Adders, as their name suggests, add binary digits. Since binary numbers consist of only two digits, 1 and 0, it is almost always necessary to carry a digit to the next higher-order column when adding.
For example 1 + 1 = 0 carry 1. There are always 3 inputs into a full adder; the 2 digits being added and the carry from the adjacent lower order column (A, B & CI)
Substractor circuits are again a combination of basic gates with the inputs A, B and BRI. BRI is the borrowed digit from the subtraction in the adjacent lower-order column (if applicable).
The outputs are D, the difference between the digits in the subtraction, and BRO, the digit borrowed from the adjacent higher-order column (if applicable).
Certain functions of a digital circuit require a consistently timed binary signal. A digital clock provides a stable frequency of binary 1 s and 0 s . A crystal material is commonly used to control pulse time and produce a consistent binary 1 and 0 waveform (square-wave).
Latches and Flip-flop circuits are a combination of logic gates that perform basic memory functions for computers and peripherals.
Both these circuits retain their output signal even when the input signal has been removed; therefore, these circuits remember the input data. The two inputs to the latch are SET (S) and RESET (R), with two output signals Q and Q (not Q). A logic 1 at the S input will set the latch memory making Q equal 1, and Q equal 0. Logic 1 at the R input will reset the latch, making Q equal 0, and Q equal 1.
Flip-flops change their output when a trigger pulse is applied. A flip-flop circuit contains three inputs, the S and R signals are identical with the latch circuit, the Clock Pulse (CP) is an input that controls the circuit switch time. Its output will only change state at given time intervals controlled by the clock pulse.
The flip-flop device when connected in series can function as a binary counter.
1
0 COUNT 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1
0 2 0
1
0 2 1
1
0 2 2
1
0 2 3
Landing Gear Logic Circuit +v THROTTLE SWITCH DOWN RIGHT MAIN GEAR DOWN SWITCH LEFT MAIN GEAR DOWN SWITCH NOSE GEAR DOWN SWITCH +v +v +v WARNING HORN Engine Starting Logic Circuit OR OR AND AND AND AND 2-3 VALVE PNEUMATIC OVER- PRESSURE (ENG 3) ENG 3 AIR No 2 ENGINE GROUND PNEUMATIC CONNECTION 1 PNEUMATIC OVER- PRESSURE (ENG 1) ENG 1 AIR 1-2 VALVE GROUND PNEUMATIC CONNECTION 2 APU LOAD CONTROL VALVE AUXILIARY POWER UNIT (APU)