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Homework Help: Question about NOR gates and overflow

  1. Jan 28, 2007 #1
    How do I develop a minimal NOR circuit that detects overflow by examining the sign bits of two addends (A and B) and their sum (S)?

    Doesn't this depend on how long the addends A and B are? Is there anyway I can generalize the result to n bit addends?

    or perhaps I can just designate one input as 'the carry in', compare the MSB of the two addends and go from there?
     
  2. jcsd
  3. Jan 28, 2007 #2
    I believe the problem requires you to consider only the MSB of A and B, and the sum S of these bits. What are the overflow conditions given these 3 inputs? Work it out from there.
     
  4. Jan 29, 2007 #3
    When adding, you MUST add two strings that are both of N bits. So, if you're adding strings of N bits, the sum of the carry out when adding the msb MUST NOT EQUAL 1.

    If it equals 1, you have overflow.

    For ex:

    If you have two 8 bit strings...

    1
    10001
    +11100
    -------
    01101

    That 1 in the bold is a carry-out, hence overflow.
     
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