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How can i build 8 bit UP/DOWN counter using two 74191?

  1. Jan 20, 2009 #1
    I need some help how to build 8 bit up/down counter for my tracking ADC. All ideas are welcome.
     
  2. jcsd
  3. Jan 20, 2009 #2

    berkeman

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    Staff: Mentor

    Check out the first thread listed below in the "Similar Threads" section. Does it help?
     
  4. Jan 20, 2009 #3
    It didn't help me so much,his circuit is more complex than mine. I need how to connect the two 74191 to built an 8 bit up/down counter.My idea of the counter is to use it as DAC as binary weighted resistors network.Finally I want to built Tracking ADC.
     
  5. Jan 20, 2009 #4

    berkeman

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    Staff: Mentor

    We don't do your school project work for you, smuscat. You need to do the bulk of the work. Show us your ideas about how to do the counter, and how you are going to use it as part of an ADC. Once you show us your work, we can offer tutorial comments that may help. You are required to do the bulk of the work on your project.
     
  6. Feb 4, 2009 #5
    I tried to build the 8bit up down counter but didn't works well.I used two 74191 ,4 input NOR gate an AND gate.The circuit is attached. The problem is when counting down.
     

    Attached Files:

  7. Feb 4, 2009 #6

    berkeman

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    Why are you using an opamp as a gate? Can you post your equations and K-Map that you used to design this? How did you derive that gate arrangement?
     
  8. Feb 4, 2009 #7
    The opamp is used as a compartor(+ i/p is from DAC, - i/p is analogue ) .When the second counter starts counting down ,the first counter is enabled to count down only when the second counter outputs are all 0.
     
  9. Feb 4, 2009 #8
    Why don't you get one counter working first and then add on the second one. Off hand it seems to me you have a number of errors. Have you looked for some application notes for the 74191? (AN 74191)
     
  10. Feb 4, 2009 #9
    I tried a single counter and it worked fine.The datasheet states that for cascading counters the ripple clock o/p of the 191 is fed to the clock i/p of the second 191 ,i tried it didn't worked when count down.My problem is when begins to count down.
     
  11. Feb 4, 2009 #10
    Which is your first 191 and which is your second?
     
  12. Feb 4, 2009 #11
    The first one is with the gates.
     
  13. Feb 4, 2009 #12
    I should have asked which is the lower 4 bit counter and which is the higher 4 bit counter?

    It also might help if you could describe how it is supposed to work count by count. What is the state of the inputs and outputs when you start? What happens when your clock ripples from the first counter to the second one?
     
  14. Feb 5, 2009 #13
    The lower bit counter is on top left corner of the image.The counter works as follows.

    First, the Data inputs of the counters are all at 0 level.

    When I load the inputs simultanously,the first counter starts to count up,when it reaches
    maxium count the counter's ripple clock is fed to the second counter and continues to count, at this stage works perfectly!

    The problem is when count down from the second counter to the first counter.

    I tried to solve the problem by making a NOR gate from the outputs of the second counter
    _
    to the input of the UP/DOWN count first counter to enable the first counter ONLY to COUNT DOWN when the outputs of the second counters are all at 0 LEVEL.
     
  15. Feb 5, 2009 #14
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