A half adder (
HA), is an
electronic component used to
add two
bits. It is distinguished from the
full adder by the
lack of a
carry in input. A half adder does, however, have a
carry out output.
Typically a half adder would be used to add the least significant bits in a ripple adder, as this addition can have no carry in. It is also significantly less complex than a full adder, and saves on hardware in the situation where a carry in is not needed.
The HA might be implemented as follows:
SUM = A xor B
Cout = A · B
Where A and B are the two bits to be added, and Cout is the bit carried out.
A possible symbol:
|
|
+--+-------+
| Cout |
--|A Sum|--
--|B HA |
| |
+----------+