I'm making a bit of progress - here are some pictures to keep you interested...
The comms is based on RS232, runs at 1204 baud and is 8 bits, 2 stop bits, odd parity, LSB first, non inverted.
It uses a single signalling wire from a (I guess) custom device that superimposes the signal onto the mains supply - it looks like it has a transformer encapsulated in it. I'm not too concerned with it at the moment as I'm monitoring from the low voltage side.
There are 3 signals plus power to the device. One appears to be a clock signal, one connects directly to the cpu, one is coupled via a pullup resistor to the cpu - presumably data in/out.
In idle the internal unit senda frames of data, 3 per second; the external sends 3 frames as well. Each frame is different but the frames repeat every second.
I'm trying to analyse the frames to work out what they contain; so far it looks like a unit id or address (it does change) (2 bytes) a zero byte, 16 bytes of data then a checksum byte.
The interesting bit will be working out what the 16 bytes are!
I have borrowed a remote control so at least I can get the unit to do things :-)
Nigel
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