Quote Originally Posted by mackrackit View Post
If you are using the same code and the same PIC® it has to be a hardware problem.

Check to OSC to make sure it is OK. Maybe wrong/bad capacitor??
Thanks for this tip! I put an Oscilloscope on to Pin 9 (OSC1) of the 18F2550MCU and it appears that the crystal is not oscillating. Can't figure out why not.
I am using an 8 MHz crystal from Abracom (their P/n ABL-8-B2) with two 27 pf capacitors as C1 and C1. This crystal specs a CL of 18 pf. By my calculation I am close to that if you assume a PCB stray capacitance of Cs=4 pf (my terminatons to crystal and capacitors from the MCU are very short on the PCB), the calculation goes like this:
CL = Cs +(c1 X c2)/(c1+c2). When usining C1=C2=27pf in this calculation CL comes out to 17.5 pf which is very close to the spec'd 18 pf and I can't believe this difference would prevent the OSC from working.
I am operating the MCU with a regulated supply voltage of 3.1 volts, so the drive on the crystal should be sufficient to cause oscillation.
One thing I really don't understand is why the MCU is still operating (granted at 38 times slower than expected) when the OSC is not even oscillating.
Can anyone give me some hints or advice how to resolve this??