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Decimal to binary

Discussion in 'Electronic Basics' started by Data888, Jan 15, 2004.

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  1. Data888

    Data888 Guest

    I have a circuit with a series of 8 decimal inputs. One line for each
    possible input. I need to convert this to a binary number of 3 digits to
    control the rest of the circuit. I can't seem to find an IC that does
    this, they all go the other way. Any suggestions?
     
  2. Priority encoder. 74HC147


    --
    *
    | __O Thomas C. Sefranek
    |_-\<,_ Amateur Radio Operator: WA1RHP
    (*)/ (*) Bicycle mobile on 145.41, 448.625 MHz

    http://hamradio.cmcorp.com/inventory/Inventory.html
    http://www.harvardrepeater.org
     
  3. ANdre H

    ANdre H Guest

    I don't know if such a IC exist, ( I am not following ICs anymore ) but you
    can build this with
    exclusive Or gates.
    b0 = c7 X c5 X c3 X c1
    b1 = c7 X c2 X c3 X c6
    b2 = c7 X c4 X c5 X c6

    X stand for exclusive OR, b0,1,2 bits, c1-7 any of our 8 inputs (0 just set
    all to zero)
    Regards
     
  4. Byron A Jeff

    Byron A Jeff Guest

    -
    --> I have a circuit with a series of 8 decimal inputs. One line for each
    -> possible input. I need to convert this to a binary number of 3 digits to
    -> control the rest of the circuit. I can't seem to find an IC that does
    -> this, they all go the other way. Any suggestions?
    ->
    -Priority encoder. 74HC147

    Just be aware that since it is a priority encoder that only the highest
    priority input will be encoded. So if input 4 and input 6 are both active,
    then the output will show 6.

    BAJ
     
  5. ---------------------------
    Assuming your 8 outputs are logic-LO:

    You route backward guard diodes from each of the 8 outputs to three
    pullup resistors, so that they pull these outputs LO when they should
    be LO: Cheap open-collector decoder. The earliest ROM was made that
    very way.

    Example, from 7 you route NO diodes, you want the outputs HI, "111",
    but from 0 you route diodes to all three outputs you want to go LO,
    from 5 you route only one diode to the 2's bit, to make "101", and
    from 2 you route two diodes to the 4's and the 1's bit, etc.

    If your outputs are open-collector-LO or active-LO,like a74LS138, then
    the decoder for 8 values, 0 through 7, takes 3+2+2+1+2+1+1+0=12 diodes
    and three 1K resistors.

    -Steve
     
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