>It is basically an 8-bit shift register timed to the serial port's speed. The byte is then sequenced into 3 different memory chips. Then once the chips are full, then it cycles to the other memory chips.
>
>Steve

Hmmm, home grown hardware? In that case, you have a lot of other issues to deal with. Rather than fight with the communication details, give these a look:

http://www.saxsoft.com/comm/info/
http://www.sofdesign.com/commtool/

They might provide the additional functionality you need. JSPayne's control appears to be a wrapper around mscomm32.ocx that provides a bit more control over the port. How it will handle your download requirements I can't say. My primary use of these things is in data logging - receive only. I do keep an old laptop around that I fire up when I need to test the captures. However, it is all in DOS doing low level writes to the ports. Good luck, it sounds like a real interesting project you've got there.