Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Digital counter small question

  1. Dec 12, 2009 #1
    hi there...
    I wanted to ask about a way to cascade or let's say connect two sets of 4-bit flipflop JK counters together..
    I want to create a circuit that is an up-down counter from 0 to 99..but as it is known, its difficult to use 8 inputs ofcourse.. so the best way is to have two sets of 4 jk flipflops..the first set will be connected to a 7seg and will count up and down, while the other one will not count up or down unless the first one has finished 10 counts..I hope u get what I mean..
    the problem is that I didnt know how to connect the first circuit with the other one, in order for the first one to trigger the second one..do u guys have any idea how can I apply this? thanx a looot in advance :)
  2. jcsd
  3. Dec 13, 2009 #2


    User Avatar
    Science Advisor

    The output of the 4th JK counter (X3 in the diagram below) falls when it clocks over from 9 to 0.
    You can use this falling pulse to clock the next set of flip flops. You could invert it if the counter needed a rising edge.

    You would wire the 1st 4 JKs as a BCD counter so that it divided by 10 but gave outputs from each stage as powers of 2.
    So the 1st stage would give a 0 or a 1 and this would be worth 0 or 1.
    But if the next stage gives a 1 it is worth 2. The next stage's 1 is worth 4 and the last one is worth 8.

    So, 1 0 0 1 is worth 9.
    Note the values from 10 to 15 cannot occur as this is a BCD counter.


    This would only count up as shown.

    However, to do what you want, you could just get a 74LS192 chip or the 4510 which can count up or down, and already give BCD out.

    If counting down wasn't important, you could get a 4518 which already has two BCD counters in the one chip, or the 40110 which already has 7 segment drivers in the counter chip. These only count up though.

    Attached Files:

    Last edited: Dec 13, 2009
  4. Dec 13, 2009 #3
    You can easily design any such counter using the K-mapping tutorial given in the instruction section of this site.

  5. Dec 19, 2009 #4
    Thanx guys that was a lot of help :) I really appreciate it..
    but now I am having a problem connecting the two IC's.. I hope I figure it out..
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook