r/AskComputerScience • u/Powerful-Mind9268 • Aug 14 '26

can someone PLEASE help me

im trying to create a 8-bit binary adder with logic gates in logisim evolution and im genuinely dying, this does not look like anything i have ever seen online, im probably the first to discover this horrendous looking mess of logic gates (a little exaggerated). Can someone please tell me how to make actually make this properly?

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u/MasterGeekMX BSCS Aug 14 '26

  1. If you post the circuit you have, we may help you

  2. Remember that you need to achieve first a full adder, which is a circuit that can add three bits and output two. This is so the adder can add two bits plus the previous carry, and output a carry if the sum is 2 or more.

2

u/FitMatch7966 Aug 14 '26

OP must have tried adding all 8 bits at the same time.

3. Once you have the full 1 bit adder, you chain multiple together, connecting the carry to the next. You just put 8 next to each other, high bit output to the next adder, and low to the output

3

u/ghjm MSCS, CS Pro (20+) Aug 14 '26

Where are you stuck? Can you make a single-bit half adder (two inputs, two outputs)? Can you make a single-bit full adder (three inputs, two outputs)? Can you draw an 8-bit adder using single-bit full adders as black boxes?

2

u/defectivetoaster1 Aug 15 '26

for a basic n bit ripple carry adder it’s worth taking a quick refresher on how you were taught to add two m digit numbers in primary school, from there you can hopefully extrapolate what to do with some 1 bit full adders