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

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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 + + +