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Old February 9th, 2018, 05:54 PM   #2
Ken Roach
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What model of PLC controller will you be using ? It might matter, because some of them treat Modbus/RTU devices like I/O (I'm thinking about the Modicon M340) but most treat them like messaging peers.

There are a handful of well regarded providers of robust Modbus/TCP to Modbus RTU bridges. The best ones, in my opinion, are:

Digi One IA

LanTronix UDS-1100-IAP


VLinx, Moxa, Advantech, Automation Direct, and ICP-DAS all make functional devices as well.

If you have something complicated to do, Prosoft or HMS Fieldbus Communicator are also options.

But don't get a general-purpose "serial server" with RS-485 on one side and Ethernet on the other. You need something that's built to understand both Modbus/TCP and Modbus RTU.

If you were using a PC and not a PLC, you might be able to use a general purpose serial server because the PC would be running a virtual serial port and could simply run a Modbus RTU driver directly. But a PLC is going to expect to use Modbus TCP, not just "encapsulated" Modbus RTU.
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