A full adder (
FA) is an
electronic component used to perform the
addition of two
bits. It is distinguished from the
half adder by having a
carry in input, as well as the two inputs for the addition. There are two outputs: a
sum output, and a
carry out. The functions might be
implemented by the following
logic:
SUM = A xor B xor Cin
Cout = (B · Cin) + (A · (B xor Cin))
Where A and B are the bits to be added, Cin is the bit carried in, and Cout is the bit carried out.
A full adder might be part of a larger ripple adder, or it might be a component in a sequential adder, as well as being present in a number of other types of circuits.
A possible symbol:
|
|
+--+-------+
| Cout |
--|A Sum|--
--|B FA |
| |
| Cin |
+--+-------+
|
|