how to use external crystal?

[tbarania]

While driving home it finally dawned on me that this might be the problem, from the data sheet:

"Fail-Safe Clock Monitor (FSCM) designed to detect a failure of the external clock source and switch detect a failure of the external clock source (LP,
XT, HS, EC or RC modes) and switch
automatically to the internal oscillator."


It may be that the external crystal isn't firing up and that is detected as a failure and the internal clock is automatically switched to. I will investigate and report back. This would explain why it seems that OSCCON doesn't work right.

[Archangel]

While driving home it finally dawned on me that this might be the problem, from the data sheet:

"Fail-Safe Clock Monitor (FSCM) designed to detect a failure of the external clock source and switch detect a failure of the external clock source (LP,
XT, HS, EC or RC modes) and switch
automatically to the internal oscillator."


It may be that the external crystal isn't firing up and that is detected as a failure and the internal clock is automatically switched to. I will investigate and report back. This would explain why it seems that OSCCON doesn't work right.

B I N G O That is where Pista1 & I were trying to take you

[Art]

I’ve been following this, but had nothing to add, so doing so silently.
You said you have a scope you should see it with a 10x probe direct to the crystal.

Any varicap across the crystal and you can change the speed of a pic output so a Human can see (maybe not 100us)
There might be a value to cause it to oscillate at startup, but will affect the accuracy greatly if left in place.

If you wet a finger and touch each crystal leg and get it to start you might just need a slightly different value for the parallel caps.

[Art]

I don’t think you actually say you’re using caps, or even a bare crystal. TTL module is even a possibility,
but if it’s a bare two pin crystal and assuming something like 22pF ceramics,
if it’s a protoboard, I recently had an experience where the clock wouldn’t start because the ground
pins of the caps were wound together, and the two disc ceramics face to face close together.