In an old DOS programm I have inherited. The inport and outport commands were used to directly write to a port address (ie. 3fc, 2fc) to control the RTS line directly. This was used as a digital I/O line for switching. I want to update this old DOS script to windows and this is my last hurdle. I have been looking at using the DTR line and opening and then closing a port (say com 2) however I still need com 1 to be able to function without interruption because it is contantly polling a radio for power out data. Does anyone have a clue how to accomplish this mess?