Showing posts from December, 2005

Old signals

I was recently approached by a company willing to give new life to old security equipment. The system had a proprietary serial bus, but the manufacturer refused to disclose any information about it. Provided it was more than twenty years old it should not be a big challenge.

However, figuring out the details of a serial communication you know nothing about will require some nice tools. This time I bought a nice USB oscilloscope. It's only 1 Mhz bandwith but fast enough for my needs in this case. With it I was able to capture bidirectional communication (as it is dual channel) and start the process of figuring it out.

Just looking at the scope signals will tell you the encoding and bitrate (look for the shortest pulses, they are likely single bits and its time-length will tell you the bitrate). Serial communication used to be mostly asyncrhonous, and this was also the case. Once the time duration of a bit known you can figure out the data length and wether parity is being used or no…