Honestly, I have NO idea. I knew nothing about how it worked (still don't really). I barely knew what a PIC was or how you actually wrote a program for it.
I had done a tiny bit of 8051 stuff in school but never quite grasped the whole programming mindset (still don't really...). All I did was etch some boards and programmed some PICs with .hex files (there was two 16C84 on each card) from the World Wide Web.

I remember that when they changed keys (or whatever) I got a bunch of cards back which needed new firmware loaded into them. It really didn't last long (might have done 15-20 cards tops) before it got to a point where they could change keys two or three times in a week and always right before a football game or in the middle of a movie "premiere" and everyone , including me and my "partner in crime" lost interest in it.