Digital Multiplier

Discussion in 'The Projects Forum' started by Joe24, Oct 14, 2007.

  1. Joe24

    Thread Starter Active Member

    May 18, 2007
    52
    0
    Hello all,

    Does anyone know how to construct a multiplier circuit using just logic gates?? Say an 4x4 bit or an 8x8 bit multiplier?

    Thanks
     
  2. Salgat

    Active Member

    Dec 23, 2006
    215
    1
    If your multiplier is by 4 or 8 you can use a bit shift circuit, but if you want a broader range then I'm not sure.
     
  3. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    I would use an EPROM, but I'm lazy.
     
  4. Joe24

    Thread Starter Active Member

    May 18, 2007
    52
    0
    No, a bit shift circuit is too limited. I need a circuit that would multiply any pair of numbers (bit sequences).
     
  5. RiJoRI

    Well-Known Member

    Aug 15, 2007
    536
    26
    Just some musings:
    You might be able to use
    * A 16-bit shift-left register with only the lower 8 bits programmable -- the upper 8 bits are always loaded with zeros.
    * An 8-bit shift-right register with the output fed to
    * a 16-bit accumulator. The accumulator adds in the value of the 16-bit register whenever the output from the 8-bit register goes high, OR when the 16-bit register is initially loaded.
    * A clock that generates 8 pulses and stops. It clocks both registers.
    * Assorted switches, resistors, and LEDs for input, run, and output.

    Timing and race conditions are left for the poor student to puzzle his or her head over.

    --Rich
     
  6. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    I second thingmaker3's EPROM approach. A 4-bit by 4-bit multiply should be fairly easy to manually create with such an approach. It has the added advantage of being very fast.

    hgmjr
     
  7. Joe24

    Thread Starter Active Member

    May 18, 2007
    52
    0
    The EPROM approach would be a good one. But, I can't use it in my project. The point is to use just logic gates.

    Here is on approach that I found in Wikipedia:

    http://en.wikipedia.org/wiki/Binary_multiplier


    Suggestions?? Comments??

    Thanks....
     
  8. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Oh, those nasty professors! Always making someone work hard to remember their lessons.:rolleyes:

    I guess I'd go with counters. Increment count by fist term, and repeat a number of times equal to second term.

    Or use an adder and a counter. Add first term to itself a number of times equal to second term.

    Aw, heck. Who are we kidding? I'd argue with the professor until I was blue in the face that EPROMs are just fancy latches and all latches are made from gates!:D
     
  9. Papabravo

    Expert

    Feb 24, 2006
    10,142
    1,790
    Try googling "Wallace Trees"
     
  10. Joe24

    Thread Starter Active Member

    May 18, 2007
    52
    0
    Yeah, that's a good argument. But now, If I use a counter, I would have to implement that counter with logic gates. No IC's are allowed basically. So what type of scheme can I use that implements the least # of gates?
     
  11. Joe24

    Thread Starter Active Member

    May 18, 2007
    52
    0
    I will do that.
     
  12. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    also check on dadda multiplier by googling:)

    moz
     
  13. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Go with PapaBravo's advice. I was quite impressed with what I found when I did. Also google "Dadda multiplier." Be sure to give PapaBravo a hearty "thank you."
     
  14. Papabravo

    Expert

    Feb 24, 2006
    10,142
    1,790
    The respect of one's peers is a precious thing to be savored and enjoyed. Thank's for those kind words.
     
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