Jan wrote an article on using Desklink over the serial port. That may be the best way of transferring files to DOS.
https://bitchin100.com/wiki/index.php?title=Jan%27s_DOS-Based_Docking_Station I get that I'm not answering your question, but that article also shows usage of commands like CTTY, setting up the baud rate in DOS, copying from the com port or console to a file, etc. -- John.
