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Homework Help: Designing 4 BIT ALU (Need Help)

  1. May 29, 2013 #1
    Hallo guys , I am first year electrical Engineer Major & we are asked to design and simulate using Multisim a small ALU ,

    The ALU is a 4-bit digital circuit that performs addition, subtraction, ANDing, ORing, complementing, XORing, XNORing and comparison.
    The ALU also outputs if the answer is negative, zero, or overflow.
    Use 3 bits to select the function of the ALU.

    I am kinda clueless where should i start , any hints on Multisim or how should i start this ? it would be really really appreciated if anyone Can contribute helping me or pointing me in the right direction .
  2. jcsd
  3. May 29, 2013 #2


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    Homework Helper
    Gold Member

    Start by putting your ALU design (or part of it, like just the adder) down on paper. Are you comfortable designing each function as a standalone (single-function ALU) circuit? If not, what are you having a problem with?

    Then you need to put one of your single-function ALU designs into Multisim. There are many digital logic tutorials available for Multisim. Have you tried getting through any of these?

    There is a tendency of some designers to put a complex design together and then test/debug it (thinking that it is not so complex, perhaps). If you can break the design down into manageable elements they become easier to test (or simulate--in this case) and troubleshoot. And you gain familiarity with Modelsim with minimal frustration.

    Finally you are going to want to put it all together. If all of your single-function ALUs work, you are practically done--do all the functions in parallel and select which output you want.
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