1. transistortransistor

    Thread Starter New Member

    Oct 9, 2013
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    [​IMG]

    I understand this BCD sum circuit. The only thing that I'm not understanding is why the last full adder carry out also triggers an 6-sum in the other part of the circuit. I mean, if the nibble is not an valid BCD number, we sum six to the number. Not valid BCD numbers are 10,11,...,15. Using K-maps you simplify this list, use an OR gate and sum six to the nibble.

    So, my question is: why the carry-out is also a trigger to sum six to the nibble? And in the same manner, why invalid nibbles also represent carry out?

    In my view, carry-out shouldnt go into that OR gate. It should be an indicator of overflow, and OR gate would be used only by the invalid nibbles.

    PS: Thread title is small, because I was getting that bug of creating a new thread blank page. I would like the title to be: "Doubt about BCD sum circuit using full adders"
     
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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  3. transistortransistor

    Thread Starter New Member

    Oct 9, 2013
    11
    0
    Got it!

    Thanks.
     
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