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TGuo0's avatar
TGuo0
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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 affec...
Abe's avatar
Abe
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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
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6 years ago

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