What is adder? Explain both of the adder (Half & Full) with proper circuit diagram and truth table.

Adder: Component of a computer processor that adds two numbers sent from the processing instructions. Adders are use not only for arithmetic logic units, but also in the other parts of the processor. They may use for calculating table index, address and many other logical work. Adders can be constructed for many numerical representation, such as binary-coded decimal or exces-3, the most common adders operate on binary numbers.

There are two types of adders:

- Half adder

Half adder

Half adder always adds only two single binary digits X and Y. It has two output, sum bit and carry bit. Sum bit represent the X-OR of X and Y, again the carry bit represent the AND of X and Y input bits.

The truth table of half adder:

INPUTS OUTPUTS

X Y SUM CARRY

0 0 0 0

0 1 1 0

1 0 1 0

1 1 0 1

Full adder

Full adder is little bit complex than half adder. Full adder has three input but two output. On the other hand half adder has only two input and two output.

A full circuit can be construct by using X-OR gate, OR gate and AND gate. The first two input is common bits and last one is called carry input.

The truth table of full adder:

INPUTS OUTPUTS

A B CIN COUT S

0 0 0 0 0

0 0 1 0 1

0 1 0 0 1

0 1 1 1 0

1 0 0 0 1

1 0 1 1 0

1 1 0 1 0

1 1 1 1 1

Summary:

From above discussion we come to know that, the use and construction of half adder and full adder, different between half adder and full adder.

References:

- Digital and computer logic diagram by M. Morris Mano

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