2 Networks on the Same Computer and Modbus TCP


Thread Starter



I have to pilot with Modbus over TCP some PLC and homemade controllers, and send files from the work computer to the machine. The machine will embed several controllers and a computer (it will send Modbus instructions). I don't want the controllers to be accessible from a different computer than the machine one.

I need the same diagram as the following one, but with Modbus TCP instead of Modbus RTU in the machine:


Is that possible to isolate two Ethernet network with the same computer?

I mean:

The machine computer can communicate with company network and receive files from workstation.

The same machine computer can send commands over Modbus TCP to PLC and controllers.

PLC and controllers have to be unaccessible from the workstation directly.

I have to use Modbus TCP instead of Modbus RTU in the machine, because we need to use PLC with Modbus TCP. And the controllers muss be used in other parts with Modbus TCP.

I hope the message clear and the project feasible.


James Ingraham

This should be trivially easy to do. Adding an additional Ethernet card to a machine is easy. You can even do it with a USB to Ethernet adapter, so that you never have to open up the PC. One caveat to this is that the two networks should be on separate subnets. For example, if the workstation is on 10.10.10.xxx, the controllers and PLC should be on something else, like 192.168.1.xxx.

Another option is to put something in between the two. For example, you could use a Data Station Plus from Red Lion or any AnyBus gateway. Those devices can sit between two networks and exchange Modbus TCP data bidirectionally, without passing any other traffic. But that's probably overkill; the second network card should do what you want.

-James Ingraham
Sage Automation, Inc.