From 2007.igem.org

Full Adder

As a future project, we would like to extend our half-adder to a full-adder, which would be much more useful as it would give us the ability to add numbers consisting of more than one digit. For example, a half-adder could perform the addition 1 + 0 = 1, or 1 + 1 = 10, but it would take a full-adder to be able to perform 1100101 + 100101.

A full-adder is a half-adder that accepts an extra input, namely the carry bit from another full-adder. Each full-adder is responsible for adding one pair of corresponding digits from the two numbers to be added, and it must add to that the carry bit from the previous full-adder. The full-adder will output the resulting sum bit and carry bit, and the process will continue until all the digits have been added. Such a chain of full-adders is called a ripple carry adder. A gene design that makes use of some of the half-adder components can be seen below.

Below is a diagram of all the outputs given all possible inputs.

A gene design that makes use of some of the half-adder components can be seen below.