Page 26 - CITS - Electronic Mechanic - TT - 2024

ELECTRONICS MECHANIC - CITS

Digital systems are more versatile
Digital circuits areless affected by noise

More digital circuitry can be fabricated on IC chips
Logic gates
Logic gates are the fundamental building blocks of digital systems. They are the physical devices that performs
the basic Boolean operations of AND,OR and NOT.
There are total seven logic gates in which three are basic logic gates (AND,OR,NOT) and two are Universal logic
gates (NAND,NOR).
Various basic gates are discussed as follows;

Not Gate
NOT gate has one inputs and one output. The output becomes logic 1 when input is at logic 0 andoutput becomes
logic 0 when the input is at logic 1. Thus it inverts or complements the logic available at input and hence called
and inverter or complement. NOTgate and its truth table are shown in fig.

NOTgate
AND Gate

AND gate means all or nothing logic
AND gate has two or more inputs and one output.The output becomes logic1only when each one of its input
is at logic1. For all other input combinations it gives output logic 0. It is represented by a symbol•.

Thus,for example, X=A·B (also written simply as X=AB) is read as “X is equal to AANDB”.
Two input AND gate and its truth table is shown below :

OR Gate:

OR gate means any or all logic
OR gate has two or more inputs and one output. The output becomes logic1 when atleast (minimum) one of the
inputs is at logic1. It is represented by a symbol+. Thus, for example, X=A+B is read as “X is equal to A OR B”.

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CITS : E & H - Electronics Mechanic - Lesson 5 - 8