ECE 375: Digital Design II

Class 27

More Advanced Adders

Full Adder → Adds 2-bits and a carry

If you are adding a 4-bit number, how many Full Adders and Half Adders are needed?

Ripple Carry Adder (RCA)

4-Bit Adder

Carry Save Adder (CSA)

Carry Save Adder

Example:

$7 + 4 + 8 =$ ?

$X$ 0 1 1 1 $7_{10}$
$Y$ 0 1 0 0 $4_{10}$
$Z$ 1 0 0 0 $8_{10}$
1 0 1 1 $S$
0 1 0 0 $C$
1 0 0 1 1 $=19_{10}$