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Modbus Communication: The Key to Building Seamless Industrial Networks
Modbus Communication: The Key to Building Seamless Industrial Networks
Overview
Modbus is a commonly used protocol in the industrial field, developed in 1979 to enable communication between automation devices. Modbus was originally implemented as an application level protocol for transmitting data through the serial layer, and now it can also be extended to be implemented through serial, TCP/IP, and User Datagram Protocol (UDP). This document provides an in-depth interpretation of the protocol implementation.
What is Modbus protocol?
Modbus is a request response protocol implemented through a master-slave relationship. In a master-slave relationship, communication always occurs in pairs (a device must initiate a request and then wait for a response), and the requesting device (master device) is responsible for initiating each interaction. Typically, the primary device is a human-machine interface (HMI) or monitoring and data acquisition (SCADA) system, while the secondary devices are sensors, programmable logic controllers (PLCs), or programmable automation controllers (PACs). The content of these requests and responses, as well as the network layer that sends these messages, are defined by different layers of the protocol.
Which devices support Modbus protocol?
The Modbus protocol is widely supported by devices, including programmable logic controllers (PLCs), remote terminal units (RTUs), sensors, actuators, human-machine interfaces (HMIs), and many other types of devices in industrial automation and industrial fields. Process Control Department. Modbus is widely used and has become the de facto standard for interoperability between devices manufactured by various manufacturers in fields such as manufacturing, energy, transportation, and building automation.
Modbus gateway is a device that converts the communication protocol used by industrial automation system network hubs. It communicates with smart devices, collects data from lower level devices and transmits it to the Modbus gateway, establishes a connection with the upper computer network, and performs Modbus protocol with network computers.
Modbus communication mode
The Modbus protocol has three main communication modes:
l RTU (Remote Terminal Unit)
l ASCII (American Standard Code for Information Interchange)
l TCP/IP (Transmission Control Protocol/Internet Protocol)
In the Modbus protocol, Modbus TCP and Modbus RTU are the two most common communication methods. Although they are all designed to facilitate data exchange between devices, there are some significant differences in their implementation methods and application scenarios.
Communication method and speed
Modbus TCP utilizes the TCP/IP protocol stack for data transmission over networks, relying on network infrastructure such as Ethernet to achieve high-speed and large-scale data transmission.
Modbus RTU, on the other hand, transmits data through serial lines such as RS-485 and RS-232, which have relatively slow transmission speeds. Data transmission and application scenarios.
Modbus RTU encapsulates data frames in a compact binary format, including address fields, function codes, data, and checksum fields. This format is efficiently transmitted in binary form, making it more suitable for real-time or local control applications, especially in environments without existing network infrastructure, such as industrial automation sites, embedded systems, sensor networks, and small control systems.
Modbus TCP, on the other hand, converts each byte of binary data into a fixed two digit hexadecimal string, which is then concatenated together and transmitted in TCP code format. Due to its simplicity, reliability, and high cost-effectiveness, it is widely used in large-scale automation systems, data centers, building automation, and industrial Internet of Things, which require long communication distances and high real-time and stability requirements for data transmission.
Application area
In the manufacturing industry, Modbus is used to connect various production equipment and achieve real-time monitoring and control of the production process; In the field of energy, it is used for the automation management of power systems, including power generation, transmission, and distribution processes; In the transportation industry, Modbus is used for urban rail transit signal systems, vehicle status monitoring, etc; In the field of building automation, Modbus is applied to HVAC, lighting, and security systems in buildings.
With the development of industrial Internet and Internet of Things technology, Modbus is also constantly innovating and upgrading to adapt to more complex and changing industrial scenarios. For example, Modbus/TCP is gradually becoming the mainstream standard for industrial Ethernet communication, and gateway devices based on Modbus enable traditional Modbus devices to easily connect to modern networks, enabling cloud storage and analysis of data.
In summary, Modbus, as a mature and widely used industrial communication protocol, has witnessed the progress of industrial automation technology and laid a solid foundation for future industrial intelligence. With the continuous development of technology, Modbus will continue to play an important role in driving innovation and change in the industrial sector.