I'm working on a little PIC project and out of sheer desperation I am
appealing to you for help!

I've designed a very simple alarm system for my house using the
PIC16F84, that uses Change on Port B Interrupt to detect whether a door
or window has opened. It then actuates a relay for an alarm and flickers

an LED to indicate on a diagram where in the house it was.

Simple to design and program using MPLAB, but when I burn it in and test

it, I find that it is VERY erratic. For instance when I apply power
(5.05v through a regulator) some LEDs flash spontaneously that are NEVER

supposed to flash and it acts strange. Normally when I then
apply Master Reset it resets properly and works fine, but not always.
Sometimes when reset it acts the same as during a power up.
Even when I think it IS working fine it sometimes does strange things
inconsistently.

I've even simulated a Power-On reset and it starts up properly in MPLAB.

BTW I've combed through the source code and everything looks fine also
in simulation.

It would be really great if you could give me some tips please. I use
12.45v to program it (unregulated) and 5.05v (regulated) for Vdd. I use
a 4MHz crystal and power up timer on, watch dog off.

Could the PIC be damaged? Why is it erratic?

Thank you!
Graham.