Quote Originally Posted by mackrackit View Post
I started playing with the 4431 DIP version and wonder if you have ran into this with the one you are using. Maybe it is a 4331 problem, maybe whole series.

When using a 4Mhz resonator and have the config set for HSPLL and DEFINE OSC 16 all works well.

If I replace the 4Mhz with a 10 Mhz and try DEFINE OSC 40 everything goes erratic.
The PIC runs but even a simple "blinky" will blink randomly.
In my haste I made the stupid mistake of NOT having capacitors near the PIC across VDD/VSS. A friend pointed this out.

The PIC runs fine at 40Mhz.