A full adder(FA) is a basic digital circuit of dual arithmetic for the addition of two binary values considering the carry. They form the basic circuit for digital adding units as they are realized in central processing units( CPU).
The full adder is a combination of two half add ers and an OR gate. In addition to the two inputs (a and b) for the digital values, full adders have a further input for the carry (u) and two outputs (s and ü).
From the mathematical function, the full adder sets the output "s" to "1" as soon as one of the three inputs has a "1". If two inputs have a "1", then the output "ü" is set to "1". If all three inputs have a "1", both outputs "s" and "ü" are set to "1". The full adder can thus add three binary numbers.