counter 0-12 rollover, DIGITAL circuits

Discussion in 'Homework Help' started by yey123, Sep 14, 2009.

  1. yey123

    Thread Starter New Member

    Jul 20, 2008
    2
    0
    I've got a problem making this circuit...

    Using the combination of D FF and JK FF or 2 D FF, i have to make a circuit that will count from 0-12...

    can anyone suggest something if what gates am i going to use or to add. And what connection will I make for it to function.

    any suggestion will surely be appreciated,,
    tnx a lot..:D
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    You could always look at a counter IC's internal logic, like a 74LS161.
     
  3. Papabravo

    Expert

    Feb 24, 2006
    10,137
    1,786
    You can't count to 12 with only 2 flipflops, never mind what type. You can only count from 0 to 3 with a pair. To count to 12 you need four flipflops. To compute this number you take the ceiling of log to the base 2 of the maximum count.
    Code ( (Unknown Language)):
    1.  
    2. ceil(log 12/log 2) = ceil(1.079181246/0.301029995)
    3.  = ceil(3.584962501)
    4.  = 4
    5.  
     
  4. Papabravo

    Expert

    Feb 24, 2006
    10,137
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    True, but the internal logic won't tell him how to go from the representation of 12 back to the representation of 0. In fact a designer may design the counter so it progresses through some other sequence of states like {3,4,5,6,7,8,9,10,11,12,13,14,15}. Most counters, like the 74xx161 have a TC output that makes this kind of syncronous reload a piece of cake.
     
  5. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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  6. Papabravo

    Expert

    Feb 24, 2006
    10,137
    1,786
    Indubiously! Except that the OP wants a divide by 13, as there are 13 elements(states) in the set {0,1,2,3,4,5,6,7,8,9,10,11,12}
     
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