full adder

An electronic digital component which performs the arithemetic addition between two numbers (fed in binary form into chip's input pins). "Full" means that the chip has carry input and output pins, to receive and transfer a carry bit from and to other adder chips connected to it in a chain. This allows additions of much larger numbers than the single chip can handle.

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     |
  +--+-------+
     |
     |