What is Modbus and how does it work?
Did you ever ask yourself what Modbus, the Modbus protocol or a Modbus plugin is? Today’s blogpost addresses these questions and explains the functionality of Modbus.
What is Modbus?
The name Modbus does not describe any hardware or software feature and is also not really a product. It is a communication protocol developed and published by Modicon systems in 1979. The Modbus protocol is used to transmit information between two or more devices via serial interface or ethernet.
It is an open protocol, available for everyone without any license fees and hence has become a de-facto standard communication protocol in several different industries.
How does Modbus work?
The Modbus protocol is based on a master-slave architecture. The master is a device or protocol controlling the slave(s), by sending or requesting data and the slave(s) responding to the master’s command. It can be connected with up to 247 slaves where each slave has an individual address from 1 to 247.
Nowadays, there are several versions of Modbus protocols. The three most common ones are Modbus TCP/IP, Modbus RTU, and Modbus ASCII. To put it simply, the main differences between those versions are the type and format of data transmission. See the following table for a basic comparison of these three versions.
| Modbus Version | Communication | Format |
| TCP/IP | Ethernet | binary |
| ASCII | serial | ASCII-Code |
| RTU | serial | binary |
Figure 1: Schematic representation of master-slave network implementing different Modbus protocols.
Good to know:
If you want to connect two devices with different ports, you should use a protocol converter. It enables the integration of devices with serial interfaces into TCP systems.
Modbus in OXYGEN
We at DEWETRON, also took advantage of the open protocol and integrated Modbus TCP/IP into our OXYGEN measurement software. By implementing the Modbus TCP plugin it is possible to read and store data from Modbus TCP clients and analyze data from the device under test (DUT). This further allows you to determine the internal state compared to the measured values.
The Modbus TCP plugin in OXYGEN is a useful feature when working with solar inverters, power converters or energy monitors. In a nutshell, it turns OXYGEN into a powerful monitoring software for Modbus and can simplify your daily tasks.
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