Can a PC communicate Modbus Plus through a serial comm port?



No, the serial port of a PC does not support Modbus Plus communication.

Modbus Plus requires both dedicated hardware and software.
A Modbus Plus card and the supporting drivers must be purchased and installed in the PC.

The Modbus Plus PC cards are detailed below:

ISA bus:

AM-SA85-030 (single cable MB+)
AM-SA85-032 (redundant cabling capable MB+)

PCI bus:

416NHM30030 (single cable MB+)
416NHM30032 (redundant cable capable MB+)
416NHM30042A (PCI-e redundant cable capable MB+)

PCMCIA cards:

416NHM21230 (type II PCMCIA card)
416NHM21233 (type III PCMCIA card)
416NHM21234 (type III PCMCIA card with PnP [plug and play] capability)

NOTE: 416NHM21234 is required for operating systems that only support PnP capable
PCMCIA cards, such as Win2000

All of the above cards include the Modbus Plus MBX driver suite CD-ROM (part number SWMXDS001)
for support with all =SA= software packages (such as Modsoft, Concept and ProWorx).