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Date: 22 Apr 2015

Half-adder is a simple combinational circuit that can add only two bits together. It is a combination of XOR gate and AND gate where XOR gate is used to perform addition and AND gate is used to get the carry output.

Boolean Function

Sum = X XOR Y;
Carry = XY

Truth Table

Input Output
x y sum carry
0 0 0 0
0 1 1 0
1 0 1 0
1 1 0 1
Logic diagram half-adder

Logic diagram for half-adder

Half-adder receives two inputs and produces two outputs. The inputs are the two bits to be added and the outputs are sum and carry.

The logic diagram for half-adder has two gates: XOR and AND. The XOR gates produces sum and AND get produces carry. For example if the inputs are 0 and 1 then the output of XOR gate will be the sum, 1 and carry, 0.

The disadvantage is that it will not be useful for adding large binary numbers.