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How can I implement this 2-bit adder circuit:

Schematic

(source)

Onto http://www.neuroproductions.be/logic-lab/ or logic.ly? After several attempts (and in spite of the half adder and full adder working) I cannot seem to get this adder working.

Here is the half adder & full adder:

Half Adder & Full Adder

Tomas
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  • We need more information to help. Please show us your half-adder, full-adder, and failed 2-bit adder. – gbulmer Sep 17 '14 at 05:04
  • @gbulmer I have now added the successful half-adder & full adder design. The failed 2-bit adder is trying to recreate the 1st image. – Tomas Sep 17 '14 at 05:21
  • I apologise, but I don't understand your problem. I think that logic-lab is a poor piece of software, but I believe I got the two-bit adder of the schematic working okay. I couldn't get the online demo of logic.ly to work, and I'm not going to install it. – gbulmer Sep 17 '14 at 12:40

2 Answers2

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It worked fine in the free online version. The only goofy thing was that I had to use these 3-to-1 outputs to get it to allow the output of one gate to go to multiple inputs of the next stage.

enter image description here

caveman
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It seems fine to me, most likely it's a incorrect software bug. I looked over the design, and that is my same design for a full adder.

OR:

You may have accidentally put a xor for the or in the 1 output, or a nand , or xnor for a input, and maybe I didn't notice it. Just look it over, and you'll get a result, likely. You have the correct design.

4BitAdder
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