Designing a circuit in Logisim that can multiple 2 8-bit numbers

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Joined Feb 22, 2017

I have to design a circuit in Logisim that can multiply two 8-bit signed binary integers in two's complement format, producing a 16-bit signed result. I would like to do this using all combinational logic. I am a novice to circuit design and I am unsure of how to go about doing this. Attached is the document I have thus far. I would like to use a series of carry-save adders to produce each of the partial products and at the end invert the partial products so that it is in two's complement format.



Joined Mar 31, 2012
Since you are a novice (as we all were at one time) I would recommend first focusing on getting a circuit to work, no matter how brute-force it might be, especially since you are doing this in simulation where gates are dirt cheap. So forget, for now, about carry-save adders and the like.

Ask yourself how YOU do it on paper with a pen an pencil. Use that as your starting point. So take out a sheet of paper and multiply two 4-bit unsigned values together, such as 1011 and 0110, and see if you can see a simple way to build a circuit that produces an 8-bit result. Now consider the impact of the 2's compliment representation and how you could accommodate that -- again, be as brute force as you need to be.

Once you understand how that first solution works, you are in a position to start seeing the patterns in the problem and its solution which puts you in a better position to understand more sophisticated approaches.