Electronic Alarms and Home Security Devices - Question on DSC PC2500

Does anyone know the protocol the PC2500 uses to talk to the keypad. There is a 4 wire connection going from the PC2500 to the keypad. One must be ground, and I assume the other is the power, which means that the other two are probably for the communications. Is it a simple serial interface? Any ideas out there? I'd like to build a circuit (or directly connect to serial port on computer) and program to tell what lights would be on on the keypad so I can have the computer inform me over the internet of what the alarm is doing.

Any thoughts?

Thanks!

The keypad interface uses a propriatory format that DSC doesn't seem inclined to share.

This is mid 1980s hardware design. The concept of consumer grade hardware having a computer wasn't even pie in the sky at the time. If you really want computer interface, a number of the newer alarm panels on the market have a couple of methods to access the alarm data via a PC.

Thanks for the reply. I figured it would be something like that, especially since my alarm is so old. I'll probably play with a scope some time to see what is going over those 4 wires. I imagine I won't be able to make heads or tails of it, but playing around will keep me out of trouble for a while

:-)

Thanks!