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Is it possible to create a full subtractor using half adders only? I have created a circuit with 2 half adders but cannot see how I can use half adders to get the borrow.

This is what I have done so far: https://i.stack.imgur.com/sO6bK.png

I need to know if this can be done using half adders only.

Algoprog
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1 Answers1

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Implementation using half subtractors only:

(a) We use the borrow out of a half subtractor to create a HS that has the same function of an AND gate.

(b) We can also use a HS with the first input = 1 to get the complementary output (the same function of a NOT gate.

We put (b) after (a)'s output and we have a NAND gate. Everything can be implemented using NAND or NOR gates. So here's the final circuit:

https://i.stack.imgur.com/cpPhN.png

We have created the equivalents of AND, OR gates using our new NAND "gates".

Algoprog
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