ECE 375: Digital Design II
Class 27More Advanced Adders
Full Adder â Adds 2-bits and a carry
If you are adding a 4-bit number, how many Full Adders and Half Adders are needed?
- 3 Full Adders
- 1 Half Adder
Ripple Carry Adder (RCA)
Carry Save Adder (CSA)
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 | $=19_{10}$ |