using 8:1 multiplexers to add 4 bit numbers

Discussion in 'Homework Help' started by kingjamesthethird, Feb 20, 2015.

  1. kingjamesthethird

    Thread Starter New Member

    Feb 20, 2015
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    Hello

    I have been asked to design a cellular logic system that uses two 8x1 multiplexers to add two 4 bit numbers. I can see how to create a full adder but am totally stumped on how to add two 4 bit numbers using only the mentioned mutliplexers. seems impossible!

    Any ideas?

    would be much appreciated, JJ
     
  2. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    Considering that the sum of two 4 bit numbers is a 5 bit number, and two 8:1 muxs can only produce 2 bits, I'd say you are correct regarding it being impossible.
     
  3. kingjamesthethird

    Thread Starter New Member

    Feb 20, 2015
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    Yes thats what I thought but then I was wondering that perhaps there is a method that involves converting the parallel data inputs into some sequenced answer using the AB inputs as a clock. seems pretty abstract I know. Anyway its good to know i havnt missed something obvious!
     
  4. WBahn

    Moderator

    Mar 31, 2012
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    Who's asked you to do this and what does it have to do with a cellular logic system?

    Are you supposed to do it with ONLY the two multiplexers?
     
  5. kingjamesthethird

    Thread Starter New Member

    Feb 20, 2015
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    Apparently I was not limited to using one cell and therefore could use as many multiplexers as I wanted as long as it was 2 per cell. It was a poorly worded question. Thanks for the help anyways
     
  6. WBahn

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    Mar 31, 2012
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    Does that mean that you have it figured out?

    I'm thinking that your use of the term "cellular" is not what I am taking it to be. Perhaps the term I might be thinking of for what you have in mind is "modular". What is meant by a "cell" in this problem?
     
  7. kingjamesthethird

    Thread Starter New Member

    Feb 20, 2015
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    yea I did it. Im no expert but I made 4 full one bit adders (each using 2 8-1 multiplexers) and stuck them together. I think its correct anyway
     
  8. kingjamesthethird

    Thread Starter New Member

    Feb 20, 2015
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    I am under the impression that each pair represents one ''cell'
     
  9. WBahn

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    Mar 31, 2012
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    But my question is, what is a "cell"? What is that term meant to encompass in this project?
     
  10. kingjamesthethird

    Thread Starter New Member

    Feb 20, 2015
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    basically a cell is part of a circuit that performs a simple operation. when lots of the same cell are attached together each can perform the operation on a particular part of the input and this combination substitutes for a more complicated circuit. thats what i learnt anyway. maybe where you come from they call it modular
     
  11. WBahn

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    Mar 31, 2012
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    Thanks. That's the conclusion I was coming to and, yes, here we would use a term like "module" or "subcircuit" instead of "cell", but that is not an unreasonable choice. Since we don't use it, however, I tend to think that you are talking about a "cell" in the same general vein as in a cellular phone system.
     
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