Comport Number

In the OPC port properties, this is a Virtual number used for reference.  The Comport can be any number. The only consideration might be to avoid conflicts with another device driver (i.e. a Serial Comport) which requires the comport number to match that of the physical interface.

The connection from the OPC Server to the PLC or automation device may be a Serial Port, TCP/IP or proprietary network card. Hence, it is possible to have a Serial connection to the device, but use the OPC Port type in WebAccess.  Allen-Bradley RS-LINX with the Data Highway protocol is an example.

If the OPC Server uses a Serial Comport, it is okay to use that same number as the OPC Comport number; this has the added advantage of reducing confusion. If the OPC Server is remote, it is best to pick a comport number above 4 (since most PC support 4 comports) and this will help prevent future conflicts.