The communications port is the link used to connect to the field devices.  It can be a "physical link" (e.g. a serial RS232 cable or an Ethernet Network) or it can be a "software link"  (e.g. an OPC Server or third party API). 

Examples include COM1, COM2 (which a serial ports on the SCADA node), TCP/IP (which is any network card using TCP/IP), an OPC Server or a proprietary network card requiring special software (API). You can change the Port type and Port Number later.

There maybe a serial port or network used to connect the SCADA node to the automation device but the equipment vendor supplies software to communicate to the device.  In this case, WebAccess communicates to API software driver associated with the serial card or network card. An API port is configured.  The Siemens S7 via SOFTNET is an example of an API interface using a network card.

Not all Device Drivers work on all Port Types.  For example, the Modicon driver works on both Serial and TCP/IP ports.  In contrast, the AXLON FBM driver supports only TCP/IP network connections.

If using multiple communications ports, determine which tags are on which comport. It's easy to change the comport number for all the tags on a comport.  It almost impossible to move only some tags from one comport to another.  However, it is possible to move all the tags to another comport by changing the comport number.