How can I write to multiple daisy-chained network serial addresses through a single COM port?

[Stu_Turner]

I have a VI to write to 3 PI Mercury motor controllers using daisy chained RS232 connected via a Prolific USB-to-Serial adapter. I know that it is possible to talk to the individual controllers because the PI terminal that I have recognises the addresses of multiple controllers and designates them Device 1,2,3. The VISA resource name when configuring the port just comes up as COM5 most of time, with seemingly no way to specify an address on that COM port. Occasionally the VISA resource is ASRL5::INSTR and as this is disconnected and re-connected, this address moves up a number (e.g ASRL7::INSTR). Can anybody tell me how I can configure my serial communication to allow me to individually communicate with the different devices through a single COM port?

[Dennis_Knutson]

What does the manual say about addressing? RS-232 is not multidrop, the resource name is correct, and there is no additional configuration needed. There would have be a specific write in order to address a certain controller.