Comprehensive analysis of Modbus protocol

The modbus protocol has become one of the most popular communication protocols in the field of industrial automation. Many industrial devices, including PLC, DCS, smart instruments, etc., are using the Modbus protocol as the communication standard between them. As of 2007, the number of Modbus nodes installed has exceeded 10 million, which shows that the protocol has been widely used and recognized.

Modbus is a communication protocol based on serial communication, which aims to provide a common communication standard for industrial sites to realize data exchange and control between different devices. The protocol was originally developed by Modicon and is now owned by Schneider Electric. Modbus protocol is an application layer protocol, which defines a common message format, enabling data exchange and control between different devices. The protocol supports different physical layers such as RS-232, RS-422, RS-485 and Ethernet, so it can be applied to different devices and networks.

Modbus is a master/slave communication protocol that provides services specified by function codes. Internet organizations access Modbus using reserved system port 502 on the TCP/IP stack. Modbus Plus is a high-speed token passing network, the working process of Modbus:

1. Modbus communication starts with the master sending a query request to the slave.

2. The slave station receives the request and parses the request content.

3. The slave station performs corresponding operations (such as reading registers or writing registers) according to the content of the request, and sends the response data back to the master station.

4. The master station receives the response data and parses the response content.

5. The master processes the response data and sends more query requests as needed.

6. This process continues until the communication is complete or an error occurs.

In Modbus communication, the master is a device such as a controller or computer, and the slaves are sensors, actuators, or other devices. The master station is responsible for initiating communication, while the slave station is responsible for performing operations and responding to the master station's request. Communication can be via serial line or Ethernet. In Modbus communication, data is organized in the form of registers and addresses are used to refer to them. The Modbus protocol supports a variety of function codes, including reading and writing registers, reading and writing coils, etc.

Application scenario:

The Modbus protocol is widely used in industrial control and monitoring applications, including automated factories, robot control, power monitoring and control, oil and gas extraction and transportation, water treatment and supply, automated buildings, and more. Modbus is also suitable for real-time data acquisition and processing, including data transmission, data monitoring and control, fault detection and diagnosis, etc.

The following are some applications of the Modbus protocol:

PLC Control: The Modbus protocol is a standard protocol for communication between many PLCs (Programmable Logic Controllers). PLC is a widely used device in the field of industrial automation, they are usually used to control and monitor various parameters in the production process, such as temperature, pressure, flow, etc.

Smart Meters: Modbus protocol is also widely used for communication between different types of smart meters, such as temperature sensors, pressure sensors, flow meters, etc. These instruments are usually used to monitor and control various parameters in the production process to ensure the stability and quality of production.

Data Acquisition Systems: The Modbus protocol can be used for communication between different types of data acquisition systems in order to collect data from different devices into one centralized location for processing and analysis. These data acquisition systems are often used to monitor the performance and status of production equipment in order to detect and solve problems in a timely manner.

SCADA system: Modbus protocol can also be used for communication between different types of SCADA (Supervisory, Control and Data Acquisition) systems in order to realize real-time monitoring and control of various parameters in the production process. These systems are often used to automate production processes to improve production efficiency and quality.

With the development of industrial automation technology, the application of Modbus protocol is also constantly developing and innovating. Here are some future trends:

Increased communication rate: With the continuous advancement of technology, the communication rate of the Modbus protocol will also continue to increase to achieve more efficient and real-time communication and control.

Integration with the Internet: With the development of the industrial Internet, the Modbus protocol will be more integrated with Internet technology to achieve remote control and monitoring between devices.

Improved security: As network security issues become increasingly prominent, the Modbus protocol will also pay more attention to the security of communication and control to protect industrial control systems from network attacks and malicious operations.

Applicability expansion: As the application of the Modbus protocol in the field of industrial automation continues to expand, it will also be more widely used in other fields, such as smart homes, smart buildings, etc., to achieve communication and control between devices.

In short, with the continuous development of industrial automation technology, the Modbus protocol will continue to evolve and innovate to meet the needs of different fields and scenarios.