4 bit ALU circuit

Discussion in 'Homework Help' started by joegreentea, Nov 22, 2011.

  1. joegreentea

    Thread Starter New Member

    Nov 22, 2011
    8
    0
    Hi,

    Suppose I have this 1-bit ALU circuit, If I need to add an overflow, should I add it between C in and C out? Eventually, I need to put the 1-bit ALU together to become 4-bit ALU with overflow.
    Please Help.
     
  2. stahta01

    Member

    Jun 9, 2011
    133
    21
    I forget how does overflow differ from carry out?

    Please give truth table.

    Tim S.
     
  3. joegreentea

    Thread Starter New Member

    Nov 22, 2011
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    0
    Or maybe they are the same, the final carry out is overflow, how about the first carry in - in the 4-bit ALU, what it suppose to be?
    Thanks,
    Danny
     
  4. Georacer

    Moderator

    Nov 25, 2009
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    If there is a carry out, then this is an indication that an overflow has occurred and thus the result is invalid. The carry in is a useful pin that does what it says. It provides a way to insert a carry in an operation. Is there something more to it?
     
  5. joegreentea

    Thread Starter New Member

    Nov 22, 2011
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    I was just curious, if I should leave it be or put a constant 0 or 1.
     
  6. Georacer

    Moderator

    Nov 25, 2009
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    You want a constant 0 there. There is no carry in in a fresh, new operation. It would be like wanting to find how much is 1+1 and adding an extra 1 (as carry in) for some reason.
     
  7. joegreentea

    Thread Starter New Member

    Nov 22, 2011
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    0
    Thanks a lot
     
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