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JK Flip-Flop in Orcad

Original poster: Finn Hammer <f-h@xxxx>

Microsim/Orcad aficionados:

Attempting to create synchronization between. 2 digital signals, I have started to test a 74HC109 flipflop against it`s truth table in Orcad 9.2.

The first problem I stumble upon is that when I put a voltage pin on Q and notQ, the probe program shows traces that are without a voltage scale. I was expecting it to show 0V and 5V. Why is that so?
At times, it shows 2 red lines instead of a Low or a High, what does that mean?

But worst of all, I cannot make it follow the truth table:
If I tie PRE and CLR to positive, then tying J high and K low should make the outputs toggle by each clock transition.

They don`t. I get the dual red lines.

So I am stuck here, seeing little sense in progressing further before the model conforms with the truth table.

Any help is appreciated.

If I configure it as a T type FF by tying J and K together it does perform as it should, but that is not good enough.

The model I use is available for download here:


Data sheet is here:


Cheers, Finn Hammer