Can't open Uno serial port from some Windows programs

Using Arduino IDE 1.x
1

I have Duemilanove and Uno boards to work with. The Duemilanove boards give me no trouble, but with one piece of data acquisition software ("ModCom" from ModCom HMI SCADA Software Weeder Technologies) refuses to talk to the Uno.

I got the following reply from Weeder Tech (who've never heard of Arduino):

Maybe it doesn't support the options that ModCom uses such as:
type = RS232
baud rate = 9600
bit length = 8
stop bit = 1
binary = true
flow control = off
DTR = disabled
RTS = disabled
If any of these settings are not supported, ModCom will respond with "The port can not be openned".

So my question is this: How do I check and/or modify these serial port settings of the Uno? I have installed the latest 8U2 code from bithub, but that didn't help.

2

Which port number did the operating system assign to the Uno?

3

Depending on which PC I try, it's been COM3, COM8, and COM5. Modcom can talk to those port numbers, but not if they're an Uno. If I set a Duemilanove to that COM port number Modcom will happily open it up and talk to it.