4 bit subtractor

Discussion in 'Homework Help' started by aruniyengar, Aug 25, 2010.

  1. aruniyengar

    Thread Starter New Member

    Aug 12, 2010
    5
    0
    hey guys i need to make a 4 bit subtractor from scrath using logic gates.
    can someone give me a boolean expression for this and a logic ciruit.
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,138
    1,787
    I could but you wouldn't learn anything. You should start with a table for a one bit subtractor without borrow. It will have four entries, one for each possible combination of 1-bit operands. You will derive two output functions: difference and borrow. From there it is easy to add the borrow condition in and you will have your answer.
     
  3. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    Doesn't the building block need 2+1 inputs (not 4)? One for each bit and one for the carry.
     
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