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How to Decode Modbus Protocol

February 20, 2019 by Oliver Rieder

The Modbus protocol was designed to be used with serial devices and applications. 

Modbus is a protocol designed to allow communication between network-attached serial devices or applications. The protocol was introduced by the Modicon corporation in 1979, primarily to enable communication in their programmable logic controllers.

Modbus has become a widely used protocol, in part because it is an open protocol that manufacturers can use with no licensing cost. In fact, it is the de-facto standard communication protocol deployed in the manufacturing and industrial fields. A Master/Slave paradigm forms the foundation of the Modbus protocol. Communication is accomplished by a Master device which makes requests of Slave devices that then return an appropriate response to the Master.

Modbus networks are usually configured with one Master device which can be communicating and receiving responses with from 1 to 247 Slave devices. The Modbus protocol is used extensively in industrial automation implementations, enacting communication between the many sensors and controllers that make up such systems. Large facilities often employ multiple Modbus networks to address separate industrial processes or production lines.

The Modbus RTU (remote terminal unit) and Modbus ASCII are the two main modes of data transmission used in the protocol. They differ in that the Modbus ASCII is more easily understood by humans as the messages it produces are in ASCII format. Modbus RTU trades the readability of its messages for more efficient data transmission.

The ability to decode and understand the messages generated by the protocol are the primary means of troubleshooting problems encountered with the Modbus network or its connected devices.


The decoding process performs a conversion of the message format used by the Modbus serial devices into information which can be understood by human system administrators. In order for IT personnel to understand the messages being produced by the Modbus network, it is essential to use a Modbus message decoder. This tool can be a tremendous asset when optimizing or debugging the network.

Problems may eventually impact your Modbus network implementation, and possessing the capacity to accurately decode Modbus messages is critical to your ability to decisively take action and solve the problem. A high-quality Modbus message decoder is an essential tool for individuals working with networks or devices that use the Modbus protocol. Serial Port Monitor is such a tool and can help you quickly identify the exact issues affecting your Modbus network.

With the rest can be found in this article.


Oliver Rieder

I'm Oliver Rieder, a freelance Technical Author and USB & COM technology expert. I've been in the industry for over 9 years now and have worked with some of the biggest names in tech.

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