Jk flip flop query

Discussion in 'Homework Help' started by monkeyhead, May 14, 2008.

  1. monkeyhead

    Thread Starter Active Member

    Mar 5, 2007
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    0
    Hi there,
    I've found in my circuit that my JK flip-flop "Q" output is stuck at logic 1.
    I've probed the input feeds to the "J" , the "K" and the clock inputs and they appear to be functioning correctly.

    Could the only cause of "Q" being stuck at logic 1 be a short circuit between say the "J" or "K" input to the "Q" output?

    Many thanks,
    Matt
     
    Last edited: May 14, 2008
  2. Caveman

    Active Member

    Apr 15, 2008
    471
    0
    Or if your power is connected incorrectly or is otherwise wrong, or your set and/or reset lines, or the chip is bad.
     
  3. monkeyhead

    Thread Starter Active Member

    Mar 5, 2007
    45
    0
    Just checked and the power is connected fine and correctly. Set and reset lines aren't being used either, nor an IC just using a JK flip-flop. As I'm simulating it at the moment. Its a count-down counter by the way.

    So would I be correct in saying that after ruling the other potential causes out that there could be a short circuit between the "J" or "K" input to the "Q" output right?

    Many thanks,

    Matt
     
  4. Caveman

    Active Member

    Apr 15, 2008
    471
    0
    If you are simulating it, then no because J and K are working correctly. If it were shorted, you would see issues with J and/or K.
     
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    If you dont use the preset and clear you should connect them to ground if they are active high as i suspect. This is because if you use TTL chips a floating input is taken as high due to the internal construction of the chips. If it is CMOS chip the inputs should be never left floating because you wont know if they are high or low.
     
  6. monkeyhead

    Thread Starter Active Member

    Mar 5, 2007
    45
    0
    Yes, but the circuit I've been given has deliberately had faults enabled using Workbench, in order for me to fault find.

    So could it still be as I originally suspected?


    Many thanks
     
  7. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,159
    What jk FF is being used?

    Can you post a diagram of the circuit? [hint: ctrl or alt print screen, paste into paint, save as jpg].
     
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