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Homework Help: Having trouble forming an equation on 2 bit subtractor

  1. Jan 19, 2017 #1
    1. The problem statement, all variables and given/known data
    We are asked to make a subtractor circuit which has a 2 bit, 2 input data.

    2. Relevant equations





    3. The attempt at a solution

    I would have a 3 bit output with one borrow. The problem is I am stuck at this point and am having troubles forming an equation. Someone lent me their diagram and this is what I have


    I have tried building this on the breadboard but it gives off an erroneous result at the 7 segment cathode with the ls48 decoder for the 4th time I assembled this. It only gives off 0 and 4 at the LED matrix when it should be 3,2,1,0. The upper LED is the rightmost bit while the third led is the third bit
  2. jcsd
  3. Jan 19, 2017 #2


    User Avatar

    Staff: Mentor

    Can you show us the truth table for the subtractor? And the K-maps that correspond to each of the outputs?
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