Tips for Debugging Crystal Oscillators

Tips for oscillator debugging

The CREATE USB Interface – where art meets electronics

    * Is the PIC's oscillator running? Look between ground and pin 13 or 14 on the PIC using a 10x oscilliscope probe (the impedance of a 1x probe is sufficiently small to kill the oscillations.) If you don't see a 20MHz waveform, did you remember to configure the programming fuses for an "HS" oscillator type?

PIC32 Oscillator Issues

If the CL for the xtal is 18 pF, then you probably need bigger caps.
The two caps are effectively in *series*, so with two 18 pF caps you really only have 9 pF load (it is really somewhat more than 9 pF, because stray capacitance adds perhaps 3 or 4 pF, depending on your PC layout).

For 18 or 20 pF xtals, common values for the caps are 33 pF. The series equivalent is then 16.5, but adding 3 or 4 pF puts you near enough to 20 pF total.