Christopher, You are understandably misinterpreting IDL's COM interface as a tool for COM Serial Port communication. It is actually a tool for interfacing IDL to other software programs through Microsoft's Component Object Model, also called "COM". IDL does not have a direct interface to the COM serial port. One of RSI's engineers, however, created with IDL CALL_EXTERNAL a library for Microsoft Windows users that interfaces IDL to a C program that can open, read from, write to and close a COM port. Here is the link to his library files and their C source code: http://www.ittvis.com/cod...k/search.asp?FID=239 James Jones