IF I WERE YOU I WOULD CHECK EVERY PIN OF THE MICROCONTROLLER THROUGH THE TIME THAT THE INITIAL RUN OF THE PROGRAM HAPPENS. NO PIN SHOULD SEE VOLTAGES BELOW GND OR ABOVE VCC. I SUSPECT THAT YOUR PROBLEM IS THAT YOU HAVE A SHORT OR WIRING MISTAKE THAT IS CAUSING ONE OF THE +12/-12 OUTPUTS OF THE RS232 DRIVER TO BE MISTAKENLY CONNECTED TO SOME MICROCONTROLLER PIN. IF A MICRO PIN IS SEEING AN OUT OF VALID RANGE VOLTAGE LEVEL THE PART IS MOST LIKELY EXPERIENCING CMOS LATCHUP. RECOVERY FROM LATCHUP COMMONLY REQUIRES EXACTLY THE STEPS YOU HAVE HAD TO TAKE.

MICHAEL KARAS