Help with Boolean circuit design

Discussion in 'Homework Help' started by Estudent1005, Jan 5, 2011.

  1. Estudent1005

    Thread Starter New Member

    Jan 5, 2011
    4
    0
    I'm stuck on this homework question and was hoping for some help:

    Design a Boolean circuit that compares whether two-bit unsigned numbers are equal.

    I was given the hint : Construct a truth table and use XOR, AND, and NOT gates.

    Any advice on this one?
     
  2. n1ist

    Active Member

    Mar 8, 2009
    171
    16
    Well, you have 4 inputs and one output. Start by drawing the truth table (what does it mean when two two-bit unsigned numbers are equal?) Then figure out the logic from that.

    /mike
     
  3. Estudent1005

    Thread Starter New Member

    Jan 5, 2011
    4
    0
    I understand the input logic (i think)

    would the inputs to the truth table look similiar to this:

    X1 X2 Y1 Y2
    0 0 0 0
    0 1 0 1
    1 0 1 0
    1 1 1 1


    how do I begin to create the Boolean function? From there, I know how to calculate the output and how to build the circuit, just stuck on the formula part..

    Thanks again!
     
    Last edited: Jan 6, 2011
  4. Estudent1005

    Thread Starter New Member

    Jan 5, 2011
    4
    0
    do I need to show 2 formulas that are equal?
    for example:

    x1 XOR x2 = y1 NOTy2 AND NOTy1 y2

    something like that?

    x1, x2, y1, y2 being my input variables
     
  5. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    The XOR gate has the property of giving a 1 if its two inputs are different. Therefore, if you pass the 4 bits through 2 XORs, and see even one 1, your numbers are different. I don't think a truth table will be of much help here. Just use your logic to sort this out.
     
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