Modbus RTU (RS-485 Cable-USB)

We have many computers with the SCADA installed (clients) around the plant. I have the Gateway Serial Support Module and the Modbus Driver module.

I’m trying to install a device that uses Modbus RTU RS-485-USB Cable.

The procedure is:
-Create a new device connection.

  • Modbus RTU.
    -Assign a name and description.
    -Assign a Serial Port (COM).

Here is my question. Can I connect my device to one of the PC ports (in the network) and assign that COM number and will it work?
In the videos, they said to assign a PORT but I think should be a COM port of the Server computer not of any computer right? (And our server is remote).

That won’t work, it would need to be connected to the gateway. This may be an application for a device like this:

I also have many 485 device need transfer the data to ignition
but I don’t use the Serial Support Module, here is my structure

  1. Use 1 siemens 1200 PLC write the PLC software to read the data from the 485 device
  2. Ignition can use opc-ua connect to that simenes PLC

I’m going to bet a Moxa NPort 5130 (RS-485 via Ethernet) is cheaper than a Siemens 1200, and requires no external programming software. The IA Modbus driver offers RTU over TCP without needing the serial support module. (As does my own Advanced Modbus driver module.)

It does, but I always recommend not using it, because RTU over TCP is conceptually flawed. Just spend the few extra dollars for the Moxa that will actually convert to Modbus TCP.

I strongly disagree. You just need to configure the intermediate device to buffer correctly, as described in my module’s user manual. A Moxa is far more reliable at such timing than any PC’s serial port.

{ Not to knock the Modbus TCP gateway product… that’s nice too. }

Meh, that you need a special application note I think favors my assertion.

Modbus ASCII over TCP, or Modbus RTU over UDP, make far more sense. Unfortunately they are pretty rare.

Meh. Ethernet to Serial converters pretty much always need some configuration, like port parameters, so noting the one other parameter to set for correct operation is not a stretch for a user. (That setting makes IA’s module behave, too.)