It turns out that creating an access card is much easier than what it might look like. Here's a decompilation of the checks the Net Yaroze boot CD: http://pastebin.com/5cySSjcn Basically the Access Card just waits for a 0x21 byte and pulls down /ACK. After that /ACK the console sends a 0x53 byte and expects a byte with upper 4 bits set to zero.
