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TGuo0's avatar
TGuo0
Icon for New Contributor rankNew Contributor
6 years ago

waveform simulation producing no output (xx) in Quartus II

Hello. So I am trying to simulate a simple JK flip-flop, and for some reason, when I try to do so, Q and Qbar stay as XX. The simulation works if I remove the clock. I don't know why that would affect anything. Please help me. I'm just a poor college student trying to graduate.

6 Replies

  • Vicky1's avatar
    Vicky1
    Icon for Regular Contributor rankRegular Contributor
    6 years ago
    Hi Tina, Please help me by providing below details, 1. which quartus(edition & version) are you using? 2. have you come across any error while simulating including clock signal? 3. provide the simulation screenshot of the result without clock signal Thanks, Vikas
    • TGuo0's avatar
      TGuo0
      Icon for New Contributor rankNew Contributor
      6 years ago

      Hello!

      1. I'm using Quartus II Web Edition 13.0sp1
      2. The screenshot above is what happens when I include clock signal
      3. The below is what happens when the clock signal to both latches are the same (so the not gate at the bottom is removed)

  • Abe's avatar
    Abe
    Icon for Frequent Contributor rankFrequent Contributor
    6 years ago

    The simulation does not work due to the inherent behavior of the JK master slave FF:

    1. If CLK is low at the start, the outputs Q and Qb will be X irrespective of the state of J and K.
    2. If CLk is high at the start and J=0 and K=1, the outputs will still be X. (K input is also Reset for SR flop which is used to build the JK master-slave)

    To get the simulation working,

    1. Shift the clock edge by some x ns so that it starts HIGH.
    2. Assign J =1 and K = 0 , this is the set condition for the FF.
    3. Follow the rest of the JK FF truth table.
    • TGuo0's avatar
      TGuo0
      Icon for New Contributor rankNew Contributor
      6 years ago

      Thanks for the clarification! Unfortunately, when I tried your suggestions, the same result came out. Is there something I'm missing?

  • Abe's avatar
    Abe
    Icon for Frequent Contributor rankFrequent Contributor
    6 years ago

    Take a look at the following projet file. It should help you. It also includes the waveform for simulation.