Combinational Logic Circuit to convert Excess 3 code into BCD code

Discussion in 'Homework Help' started by hitmen, Mar 11, 2009.

  1. hitmen

    hitmen Thread Starter Active Member

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    I know that -3 = 0000
    -2 = 0001
    -1 = 0010
    and that 10, 11, 12 are dont care conditions.

    But how do I implement the K-map?
  2. beenthere

    beenthere AAC Fanatic!

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    Make a table of the excess 3 codes and their BCD equivalents. Work from that.
  3. hitmen

    hitmen Thread Starter Active Member

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    Table ? I dont exactly understand.

    -3 = 0000
    -2 = 0001
    -1 = 0010 (These 3 dont care)

    0 = 0011
    1 = 0100
    2 = 0101
    3 = 0110
    4 = 0111
    5 = 1000
    6 = 1001
    7 = 1010
    8 = 1011
    9 = 1100
    10 onwards not possible dont care

    Where do I go from here?
  4. beenthere

    beenthere AAC Fanatic!

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    Think of your excess 3 codes being applied as select bits to some multiplexers.
  5. vvkannan

    vvkannan Active Member

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    Hello hitmen,

    Set up a 4 variable k-map . The input variables A,B,C,D are the
    excess-3 code bits(starting from 0011 ,which corresponds to A'B'CD) . This is for the first bit of all the output values(which is BCD ).

    Similarly do it for the other 3 bits which means you will get 4 K-maps in all
  6. hitmen

    hitmen Thread Starter Active Member

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    Hi vvkannan,

    I understand how to do the question already. But how do the examiners know whether your answer is right or wrong since there are so many dont care conditions? Also, how can a student verify his answer?
  7. vvkannan

    vvkannan Active Member

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    First of all i am an undergraduate student and i don't have any experience in correction ;). I studied this subject last semester.

    But yes you are right ,we can have many answers for these type of questions.
    We try to get the simplified form which uses the minimum number of gates and incase of dontcares just give them the value which reduces the total number of inputs and gates.
    But i think you can have many answers
  8. hitmen

    hitmen Thread Starter Active Member

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    undergradate? so am I.
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