When you prolong the clearing signal duration, it will clear the flip-flops properly and the problem disappears - see the modified schematic diagram, where the clr signal is hold at L level for one half of the clock period. That's why at the next counting edge at 4.5us the value of Q1 cannot be determined (see the waveform diagram - the red waveform Q1) - because of the 'PERSISTENT ERROR at "CLEAR" input of X_U1A' (your error message). One and only one of these parameters must be given. ![]() The waveform diagram shows that the value of Q3 and 'clr' (Q3bar) is due to it undefined from that time on. The series is a set of tutorials and information on SPICE simulation, OrCAD pSPICE compatibility, SPICE modeling. lib and allow you to add whatever values you’d like. The model editor will open the mosfet model in the library breakout. The time of the generated impulse is too short to clear the flip-flops. How do I change MOSFET parameters in PSpice Right click the part and select edit properties to set up a few of the device values from the schematic page or right click the part and select edit model. ![]() after ~3.5us, it comes to a "problem" because the inverted output Q3bar=L (signal clr) would immediately clear all the three flip-flops, and therefore, it tries to set back to Q3bar=H also itself. ![]() Your circuit works as an asynchronous binary counter, changing its count at every falling edge of the input clock (stimulus DSTM1), starting at 0,0,0 state (Q3,Q2,Q1 according to my schematic_diagram).Īs soon as the count reaches 1,1,1, i.e.
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