A 4bit ripple carry adder consists of one half adder and three
full adder. A half adder has two inputs (**a** and **b**), least
significant bits (LSB) of each operand, and two outputs, **sum** and
**carry**. A full adder has one additional input, **cin**, carry input
from the lower bit. In a half adder, two outputs are given by
the following formulas:

where @ and * stand for * Exclusive-Or* and * And* in XDE's
notation respectively. In a full adder, outputs are given as follows:

where + stands for * Or* in XDE. **carry** is first generated at
LSB and propagated to MSB. Hence this type of adder is called
* ripple carry*. By connecting **carry** and **cin** of these half
adder and full adders we can configure a 4bit adder.

All Rights Reserved

Thu Dec 21 01:06:46 EST 1995