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Ripple-carry adder (8 bit)

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Circuit Description

A standard 8-bit ripple-carry adder built as a cascade from eight 1-bit full-adders. Click the input switches or use the following bindkeys: ('c') for carry-in, ('a','s', ..., 'k') for A0..A7 and ('1','2', ..., '8') for B0..B7.

To demonstrate the typical behavior of the ripple-carry adder, very large gate-delays are used for the gates inside the 1-bit adders - resulting in an addition time of about 0.6 seconds per adder.

Note that each stage of the adder has to wait until the previous stage has calculated and propagates its carry output signal. Obviously, the longest delay results for operands like A = 0b0000000, B=0b11111111 or A=0b01010101 and B=0b10101010 (select these, and then switch carry-in to both 0 and 1, and watch the circuit to settle). Therefore, the total delay of a ripple-carry adder is proportional to the number of bits. Faster adders are often required for bit widths of 16 or greater.

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Impressum http://tams-www.informatik.uni-hamburg.de/applets/hades/webdemos/20-arithmetic/10-adders/ripple.html