Hi Henrik,

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.

Here is the very simple code and configs I was playing with to set the OSC.
Code:
    @ __CONFIG    _CONFIG1H, _OSC_HSPLL_1H
    @ __CONFIG    _CONFIG2H, _WDTEN_ON_2H & _WDPS_512_2H
    @ __CONFIG    _CONFIG2L, _BOREN_OFF_2L & _PWRTEN_ON_2L    
    @ __CONFIG    _CONFIG3H, _MCLRE_OFF_3H
    @ __CONFIG    _CONFIG4L, _LVP_OFF_4L  
    
     DEFINE OSC 16
     
    START:HIGH PORTD.1:PAUSE 500
    LOW PORTD.1:PAUSE 500:GOTO START