Connect the TSXSCA72 to a PC using a serial to usb cable converter


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I need to connect the SCA72 (rs485 to rs232 converter) to a pc using the usb port. I´m trying to do this using a prolific drive to the usb serial converter and using unitelway driver to comunicate the pc to plc, but something always go wrong. Can somebody help me? I have tested many different configurations in the unitelway and proific drives, but still no success. tanx
1) Is the COM port in use by something else? Like RSLinx? or Palm's synch program?

2) Some RS-232 to USB converters work better than others.

I use two, either has yet to balk on me: Saelig brand

or Keyspan (, part number USA-19QW (a rumored high speed model is USA-HS19, but I don't have that model).

As an aside for those reading this that do Rockwell A-B PLCs:
Recommendations for Rockwell A-B devices:
Keyspan model HS19 for DF1, Modbus, and ASCII connectivity
A-B model 1747-UIC for DH-485 connectivity

3) I've heard reports of laptop IR ports interfering with USB-serial conversion, where turning the IR port off made it work.