News #002 – Modbus RTU over TCP/IP

How to use Studer Modbus RTU protocol over TCP/IP?!


A serial communication protocol developed by Modicon published by Modicon® in 1979 for use with its programmable logic controllers (PLCs). In simple terms, it is a method used for transmitting information over serial lines between electronic devices.
The device requesting the information is called the Modbus Master and the devices supplying information are Modbus Slaves. In a standard Modbus network, there is one Master and up to 247 Slaves, each with a unique Slave Address from 1 to 247. The Master can also write information to the Slaves. The official Modbus specification can be found at .

How it’s works?

Modbus over TCP/IP or Modbus over TCP or Modbus RTU/IP: This is a Modbus variant that differs from Modbus TCP in that a checksum is included in the payload as with Modbus RTU. Data model and function calls are identical for the previous 4 variants of protocols; only the encapsulation is different.


This manual explain how to use and configure the Moxa NPort 5130A/5150A for connecting the Xcom-485i in your Local Area Network in order to using Modbus RTU Protocol over TCP/IP. Take this document as reference and feel free to modify according to your solution.

This solution will not transform the Modbus RTU protocol into Modbus TCP/IP protocol.

What I need?

The NPort device server will make Studer’s devices network-ready in an instant, with a compact size and just one serial port 485 the Nport 5130A/5150A is ideal for connecting to IP-based Ethernet LAN for our scope. Other NPort models from the series N5100 could be used depending on request.
• Moxa NPort 5130A
• CBL-RJ45F9-150
• Xcom-485i
All devices are available here.