Hi Allison, Humm... the NEC databook that I have makes no mention of a "READ DIAGNSTIC" command is this an undocumented feature or later version enhancement? If I can read "bad sectors", even with errors, I can add another Sector Data Block flag byte value which means "data but with errors". Can you give me details or point me at a reference which documents this and any other features not in the NEC data sheet? Regards, Dave -- dave04a (at) Dave Dunfield dunfield (dot) Firmware development services & tools: www.dunfield.com com Collector of vintage computing equipment: http://www.parse.com/~ddunfield/museum/index.html