Modbus RTU (RS-485 Cable-USB)

Ignition
1

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.
    NEXT
    -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).

2

That won’t work, it would need to be connected to the gateway. This may be an application for a device like this:
https://www.digi.com/products/networking/infrastructure-management/usb-connectivity/usb-over-ip/anywhereusb

3

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

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4

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.)

5

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.

6

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. }

7

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.

8

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.)