There are times when we want to add a collection of numbers together. Suppose you wanted to add four 4-bit numbers (A, B, E, F) using 1-bit full adders. Let?s ignore carry lookahead for now. You would likely connect the 1-bit adders in the organization at the top of Figure B.14.1. Below the traditional organization is a novel organization of full adders. Try adding four numbers using both organizations to convince yourself that you get the same answer.

Figure B.14.1

a3 b3 a2 b2 a1 b1 a0 b0 A B E F Traditional adder e3 e2 e1 e0 + Traditional adder f3 f2 f1 f0 Traditional adder $5 s4 s3 s2 s1 s0 b3 e3 f3 b2 e2 f2 b1 et f1 b0 e0 fo A B E + Carry save adder a3 a2 a1 a0 Carry save adder c S s'4 c'3 s'3c2 s'2 |c'1 s'1 (c'0 s'0 Traditional adder $5 s4 s3 s2 s1 s0 + + +