Half Adder in Digital Logic

Half Adder ( HA )

The addition of 2 bits is done using a combination circuit called a Half adder. The input variables are augend and addend bits and output variables are sum & carry bits. A and B are the two input bits.

Truth Table:

Here we perform two operations Sum and Carry, thus we need two K-maps one for each to derive the expression.

Logical Expression: 

             1) for Sum:
                                   

                                                                                                         Sum = A XOR B

           2) for Carry: 
                               

                                                                                                       Carry = A AND B 

Implementation:

Note:

          Half adder has only two inputs and there is no provision to add a carry coming from the lower order bits when multi addition is performed.

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