Last week I was playing around with understanding serial protocol between RFID reader and computer. For a start, I had a windows application which could communicate with RFID reader over USB serial adapter (which is included in device, so device looks like USB device).
First, I needed to sniff USB serial traffic under Windows to understand protocol between device and program.
Then I wrote a simple script to reformat output from portmon to more readable format, and found out that packets have two byte checksum in them.
After I tried all simple combinations to produce valid checksum, I decided to ask a question about checksum guessing at stackoverflow.com. This was great idea, because selwyn stepped in and confirmed that my checksum is CCITT.
Having all that parts in place, next step was to write perl script using Device::SerialPort to communicate with serial port, and thus RFID reader. Right now, I'm pondering how to integrate it with Koha, but that's topic for another post...