Do a search for 'xmodem'. This is a file transfer protocol that is supported by many terminal programs such as the much maligned Hyperterminal. (BTW Why is Hyperterminal hated so much?? I have no problems with it). Implement xmodem (or some other protocol) for your file transfer and your problem is solved. If you want an application on the PC side of things, then try Delphi with the asyncpro tools which have Xmodem as part of the toolset. Job done.