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D Flip Flop Question (not working?)

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jdwoodall
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D Flip Flop Question (not working?)

I have a simple divide by 2 circuit.   I have built this same circuit 100's of times.   Using the ngspice library D-FF, both Q and Q-Not are high.  I have set R & S to both 1 and zero with no change.  Both outputs are always high.  Something seems very broking.  Any ideas?  Thanks in advance.

 

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cacklestein
in reply to: jdwoodall

The DFF starts in an indeterminate state. You need to toggle set or reset (but not both simultaneously) at startup to move the DFF into a particular state before proceeding. They are both positive logic. So one way to get this to work is to hold the SET line continually low, and to perform an initial toggle of the RESET signal.

Initial reset of DFFInitial reset of DFF



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