Content originally posted in LPCWare by IanB on Wed Nov 25 03:29:32 MST 2015
is it oscillating? The odds are it is - either put an oscilloscope on XTALOUT (not XTALIN because the probe capacitance will stop it working).
Or use the processor to check if the counter is counting.
If it is oscillating, how accurate do you need it?
If you need it REALLY accuracy, then make the cap on XTALIN a trimmer, and set it with a frequency counter. You never really do know the value of Cstray
If you don't need it REALLY accurate, at a guess it's already good enough.
I built a similar circuit, and I had just two 15pF capacitors left, and one fell on the floor never to be seen again.
It still worked without the capacitor in XTALOUT.
I keep 15pF capacitors in stock and use then on crystal oscillators without ever bothering to check if it is the right value, and they have all worked.