Introduction and characteristics of Modbus protocol

Modbus was invented by Modicon (now a brand of Schneider Electric) in 1979 and is the world's first bus protocol that is truly used in industrial sites. In order to better popularize and promote the distributed application of Modbus on the Ethernet, Schneider has transferred the ownership of the Modbus protocol to the IDA (Interface for Distributed AutomaTIon, distributed automation interface) organization, and established the Modbus-IDA organization. Laid the foundation for the future development of Modbus. In China, Modbus has become the national standard GB / T19582-2008. According to incomplete statistics: As of 2007, the number of Modbus node installations has exceeded 10 million.

Modbus protocol is a general language applied to electronic controllers. Through this protocol, the controllers can communicate with each other, and the controller can communicate with other devices via a network (such as Ethernet). It has become a universal industry standard. With it, control equipment produced by different manufacturers can be connected into an industrial network for centralized monitoring. This protocol defines a message structure that a controller can recognize and use regardless of the network through which they communicate. It describes the process of a controller requesting access to other devices, how to respond to requests from other devices, and how to detect and record errors. It establishes the format of the message domain and the common format of the content.

When communicating on a Modbus network, this protocol determines that each controller needs to know their device address, identify the messages sent by the address, and decide what action to take. If a response is required, the controller will generate feedback information and send it using Modbus protocol. On other networks, messages that contain Modbus protocol are converted into frames or packet structures used on this network. This conversion also extends the method of solving section addresses, routing paths, and error detection according to specific networks.


Modbus has the following characteristics:

(1) Standard and open, users can use the Modbus protocol free of charge, without worrying about paying license fees and infringing intellectual property rights. Currently, there are more than 400 manufacturers supporting Modbus and more than 600 products supporting Modbus.

(2) Modbus can support a variety of electrical interfaces, such as RS-232, RS-485, etc., and can also be transmitted on various media, such as twisted pair, optical fiber, wireless, etc.

(3) The frame format of Modbus is simple, compact and easy to understand. The user is easy to use, and the manufacturer's development is simple.

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