GOTO statement causing jitter in output frequency, can be this fixed?

[CuriousOne]

No it is not obvious, because it takes DIFFERENT times on each iteration of GOTO statement.

[tumbleweed]

If you reduce the timebase of your analyzer so you can capture an entire set of the FOR-NEXT loop, you'll see that it's not jitter but the increased time when the FOR-NEXT loop exits and the GOTO loop occurs. You have a few extra cycles there to do the GOTO and the exit/initialization of the FOR-NEXT loop so every 16 iterations you get a small gap.

The code I posted takes advantage of the fact that incrementing a byte from 255 just rolls over to 0, so it has the same effect as your FOR x=0 to 15 loop without the extra loop involved.

Obviously, your pic can't do anything else but this, otherwise the timing will change. Your other option would be to setup a timer and do this in an interrupt routine but you won't be able to get exact timing with that since there can be a slight difference in the timing of when the ISR runs.

[HenrikOlsson]

And since the four pins are on the same port you could do away with the individual RMW-instructions for each pin and just do

x = 0
masfrk:
  PortC = x
  x = x + 16
  pauseus 194
goto masfrk

Or even

PortC = 0
masfrk:
  PortC = PortC + 16
  pauseus 194
goto masfrk

Obviously this will cause the bottom 4 bits of PortC to be 0 but it doesn't look like you're using those for anything.