PSS does not converge if initial condition is set

The convergence problem is probably that you don't have the PSS fundamental frequency set correctly, or that you didn't give a long enough time for the tstab to ensure the divider is correctly working. I don't quite see from the above what the circuit is supposed to be doing (since it appears to be a shift register rather than a divider. If it's a divider, did you set the PSS frequency to the divided down frequency (rather than the input frequency)? Are there any even lower frequencies in the circuit (sub-harmonics)? If so, your PSS fundamental needs to reflect that as all frequencies in the circuit need to be an integer multiple of the PSS fundamental.

Andrew

That right! You have pointed out the problem that I didn't notice the lowest frequency was changed to one eighth of the original frequency. Thank you very much!

Dear jandk,

jandk said:

nd if I don't set the initial condition, the PSS converges but the circuit does not work(circuit nodes do not see any level changes). 

I fear a second issue may be that without your initial condition, the circuit (which appears to be a divider), is that the circuit will not function unless you ensure the output of one flip-flop has a different state than the remaining flip-flop outputs. For example if all outputs come up in the logic low state, as the input clock advances, all the flip-flops will remain in the logic low state and hence will not form a divide-by-8 of the input clock frequency.

Shawn

That's right. If I don't give the initial logic state, all nodes will keep the same voltage level all the time.