How to implement a Excess 3 to BCD Converter?

Discussion in 'Homework Help' started by The Rock, Sep 25, 2011.

  1. The Rock

    The Rock Thread Starter New Member

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    I need to convert Excess 3 to BCD.
    What are my inputs in the truth tables so that i can do the K Maps?
    I understand that
    -3 = 0000 ( Don't care)
    -2 = 0001 ( Don't care)
    -1 = 0010 ( Don't care )
    0 = 0011
    1 = 0100
    etc n so on..until 10, 11, 12 are also don't cares.

    Do i need to put the don't cares in the Excess 3 Code column? Plzz help! Thanks.
  2. Georacer

    Georacer Moderator Staff Member

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    If your input and output are 4 bits long, you could make 4 4-input Boolean functions that will take the Excess 3 number and produce one digit of the output each. You will end up with a medium-sizes combinatorial circuit, which can be implemented either with simple gates or with MUXs.

    Is that clear?

    Post a conversion truth table if you need more help.
  3. The Rock

    The Rock Thread Starter New Member

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    Can u post the conversion truth table for me? Its still vague for me...
    By the question, i think we need to implement it using K maps for each input used n construct the circuit as per the K map!
  4. Georacer

    Georacer Moderator Staff Member

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    Your thinking this correct.

    You started the truth table correctly yourself, you just need to finish it:
    Code:
    Excess 3 | BCD (D3D2D1D0)
    -----------------
      0000    | XXXX
      0001    | XXXX
      0010    | XXXX
      0011    | 0000
    
    and so on.
    You got four Boolean functions, D3, D2, D1 and D0 that will give you an output digit of the result depending on the 4 input digits.

    Don't forget that BCD numbering doesn't go beyond 9.
  5. The Rock

    The Rock Thread Starter New Member

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    Thanks A Lot, Georacer!
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