Metastability in jk flipflop

Discussion in 'The Projects Forum' started by imbaine13, Sep 16, 2015.

  1. imbaine13

    Thread Starter Member

    Oct 6, 2013
    Hello everyone,
    I long while ago, I asked this same thing but didn't get directions responses. I hope it works out better this time. I'm building a unipolar stepper motor driver with step and direction inputs, using a counter and decoder to drive mosfets which will in turn power the motor coils in sequence.
    I'm very aware and actually have bought chips dedicated for these particular purposes, but seeing as their operation can seemingly easily be done using discrete flip flops, I thought I'd give it a shot. Mostly to better understand the underlying concepts. However, as I fiddled around trying to understand the jk flipflop, I wondered what would happen if ALL INPUTS (j, k and clk) were all rising instantaneously. A better way to put it is, what would happen if I used a jk latch instead of a jk flipflop, and kept the enable high, while both the j and k were held high. Would the outputs oscillate?
    I also came across this article on Wikipedia which reinforced my curiosity!
    Could this be what would happen?

    Appreciate your feedback!
    Lovely time!
  2. imbaine13

    Thread Starter Member

    Oct 6, 2013
  3. crutschow


    Mar 14, 2008
    Normally you don't want to put all inputs high at the same time.
    The result may not be "metastable" but it's certainly undefined.
  4. Brownout

    Well-Known Member

    Jan 10, 2012
    That's not a better way to put it. That's a completely different question. The output is very likely to oscillate. At best, the output is indeterminent.
  5. imbaine13

    Thread Starter Member

    Oct 6, 2013
    Thanks guys. Really helpful. I suppose I just needed a second opinion.
    God bless you all!