Digital Electronics - Full Adder

Discussion in 'Homework Help' started by cheyenne, Feb 4, 2008.

  1. cheyenne

    Thread Starter Active Member

    Dec 6, 2007
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    I have a question asking me to design a logic circuit for a full adder using NAND gates.

    I am finding it hard understanding this topic. Can someone explain to me how the outputs of the truth table are determined so I can understand this better.
     
  2. Dave

    Retired Moderator

    Nov 17, 2003
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  3. Papabravo

    Expert

    Feb 24, 2006
    10,135
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    Well the outputs in the truth table follow the rules for binary addition. You use the same intuition that you have for decimal addition except you remember that you are in base 2 instead of base 10.
    Code ( (Unknown Language)):
    1.  
    2. 0 + 0 = 0   in any number base
    3. 0 + 1 = 1   also true in any number base
    4. 1 + 0 = 1   addition is commutative
    5. 1 + 1 = 0   makes sense if you remembered to say "and carry the 1".
    6.  
    The Booleanly astute will recognize that the truth table for the binary sum is the same as the truth table for the exclusive-OR function. I leave the truth table for the carry bit as an exercise for the reader.
     
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