Half Adder

A half adder adds 2 bits to give us the sum and the carry bit.

a b | sum carry

----------------

0 0 | 0 0

0 1 | 1 0

1 0 | 1 0

1 1 | 0 1

Now we need to implement this in logic using the basic gates we have built till now.

We will use different logic for the sum and carry bits.

a b | sum

----------

0 0 | 0

0 1 | 1

1 0 | 1

1 1 | 0

The above truth table is that of an XOR chip.

a b | carry

----------------

0 0 | 0

0 1 | 0

1 0 | 0

1 1 | 1

The above truth table is that of an AND chip.

From the above inferences, we can implement a half adder using an XOR, and AND chip.

Here is the HDL code of a Half Adder.