changing osc on the fly

[Dave]

Art, What would you use as a reference in that situation?

Dave Purola,
N8NTA

[Bruce]

If you have a PIC that supports Internal/External Oscillator Switchover then you shouldn't need a firmware solution to determine osc speed. You already know what it should be after you write to OSCCON & flip the System Clock Select bit.

If you have one running on the internal oscillator, and you need to calibrate it, then Microchip has a few app notes for this using TMR1 with an external 32.768kHz watch type crystal. Or you could just output the internal clock on OSC2/CLKO and test it with an O-scope.