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what are various logic gates ? how does they work?

Basic logic gates
There are three basic gates, namely, OR gate, AND gate and NOT gate.

1. The OR gate.
For an OR gate there can be two or more inputs and an output. A and B are the inputs and Y is the output. Bolean expression for OR gate is A + B = Y, which reads A or B equals Y. The concept of addition should not be associated with the indicated symbol (+). This equation conveys only ideas and not numbers. The logic gate symbol of the OR gate is show in figure.

The OR gate operation is analogous to two switches in parallel.

The truth table of OR gate

A B C
0 0 0
1 0 1
0 1 1
1 1 1

The AND gate

For and AND gate there are two or more inputs and an output; A and B are the inputs and Y is the output. Boolean expression for AND gate is A, B or AB = Y, which reads A and B equals Y. The logic gate symbol of AND gate is shown in figure.

Truth table for AND gate

A B Y=A*B
0 0 0
1 0 0
0 1 0
1 1 1

  

The NOT gate (Inverter)

It is a single input gate for which the output is always the complement of the input. Complement of 1 is zero and that of zero is 1. The complement of A is indicated by A' (A prime) or  (A bar). Logic gate symbol for NOT gate is shown in figure. The truth table for NOT gate is also given.

A Y=
0 1
1 0



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