TOTALLY SURPRISED..........................

I have a basic ciruit in which a PIC is supposed to flash a few LEDs. It flashes on and off PORTA and PORTB (at twice the speed of PORTA). The micro is a PIC16F628A which is setup for using its internal osc. Power supply is stable (or at least it should be, 7805 with caps on either side). It works BUT about a quater of the time the chip does very weird things. Both ports flash on and off very quickly, as well as the osc output, you see the 8mhz signal on the scope, then nothing, then 8mhz, seems like the whole chip is switching on and off in some weird loop.

Does it seem to me that there is some pins withou pull-down/pull-up resistors. If your code is ok, try pulling down/up some unused pins, or configure the unused pins to output, to prevent noises like this.

regards, and good luck

btminzon