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I am building a simple remote monitoring/control system based on MODBUS RTU I/O´s, RS485, DDNS and WEB based HMI.

There are 2 choises in the Services/RS 485 configuration module that seems relevant: "Over IP" and "Modbus Gateway". What is the difference between these two, and which should be used?

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Hello,

The Over IP serial type is used to manage serial connections over a TCP/IP network.  

The Modbus Gateway serial type allows redirecting TCP data coming to a specific port to an RTU specified by the slave ID. The slave ID can be specified by the user or be obtained directly from the Modbus header.

Regards.

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Hello back,

Yes, this is what it says in the manual, but I don´t really understand the difference. Which is the better choise for remote manitoring/control?
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Hi,

Could you explain your vision of what do you expect to control (how) in your use case and I will recommend the most fitting option.

Regards.
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It´s quite simple: the chain consists of:

* some I/O slave devices communicating with Modbus RTU protocol over RS485

* TRB255 configured for transparent communication to/from RS485 connection over 4G

* Dynamic DNS service from Loopia.se

* HMI programme working with Modubus RTU over internett
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Hi,

In your case Over IP control mode should be sufficient enough. With this method, you should be able to reach your devices connected to the router via the RS485 serial port.