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How can you design a 3 bit adder using a 4 bit adder? The description and/or the circuit's scheme would be great.

Iulia
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A 4 bit adder typically has 9 inputs:A0, A1, A2, A3, B0, B1, B2, B3 and carry-in. On the output side you'll find 5 outputs Sum0, Sum1, Sum2, Sum3 and carry-out. To use such a circuit as 3 bit adder, you simply fead 0 as input-value for the most-significant input lines A3 and B3. Ouput Sum3 will then serve as carry-out. The picture was taken from cpuville.com

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Axel Kemper
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