On Fri, 24 Dec 2004, Dwight K. Elvey wrote: Well, the CP/M side certainly has no protocol issues, the program talks to the IO port hardware directly: foo: in someport ani somebit jz foo mov a, c out someotherport ret Minicom has no XON/XOFF, and no hardware handshake, and in any case, only three wires. I really think it's code incompatibility. The original xmodem did checksum per block only; CRC was added later. There's some trick to autodetect, I forget what it is. My xmodem code is really old, old enough I had to work the protocol out from Ward's code; mine's written in BDS C. (I documented it back then and will dig up the doc. I probably wasn't the only one to do this.). It could be simply my xmodem protocol is bad. It's not really a good way to send the files, but I wanted to get everything working again.