Comprehensive Analysis of Siemens PLC Communication Protocols: A Guide to Applications of PROFIBUS, PROFINET, Modbus, and Other Network Technologies

Follow us | Discover more exciting content

Alright, I will write this technical article about PLC communication protocols as “Pig Brother”.

Hello everyone, today we will talk about the “nervous system” of industrial automation – PLC communication protocols. In the industrial field, data transmission between devices is as important as the human nervous system. This article will focus on several mainstream communication protocols to help everyone understand their characteristics and application scenarios.

1

Overview of Industrial Communication Protocols

Industrial communication protocols are like the “language” for communication between devices. Different brands and types of devices need a unified standard to achieve data exchange. For example, to control a variable frequency drive to change the motor speed or to read the measurement values from sensors, communication protocols are required.

2

Detailed Explanation of PROFIBUS

PROFIBUS (Process Field Bus) is one of the most widely used fieldbus systems today. It acts like the “Mandarin” among industrial devices, allowing devices from different manufacturers to understand each other.

Hardware Connection

• Uses RS485 interface
• Must use dedicated purple PROFIBUS cables
• Termination resistors are required at both ends (many beginners often forget this)
• Maximum transmission rate of 12Mbps
• Single bus supports up to 32 nodes

Common Configuration Steps

1. Add DP master station in hardware configuration
2. Import GSD file (device description file)
3. Set slave address (ensure no duplicates)
4. Configure data exchange area
5. Download program and test communication

Practical Application Case

Once in a paper mill, a production line with several variable frequency drives needed centralized control by a PLC. Considering the long distance and high anti-interference requirements, the PROFIBUS-DP solution was chosen. One pitfall encountered during configuration was the mismatch between the GSD file version and the actual device, leading to unstable communication. The issue was finally resolved by updating the GSD file.

3

PROFINET Technology

PROFINET is a type of industrial Ethernet, which can be understood as an industrial version of network communication. Compared to PROFIBUS, it is faster and more powerful.

Main Features

• Uses standard Ethernet interface
• Transmission rate can reach 100Mbps
• Supports TCP/IP protocol
• Can achieve real-time communication
• Supports network diagnostic functions

Configuration Points

1. Set IP address and subnet mask
2. Assign device name
3. Configure IO data area
4. Use system functions in the program to read and write data

Usage Experience

In a project to upgrade an injection molding machine, the original use of PROFIBUS was upgraded to PROFINET, which not only improved response speed but also allowed direct viewing of device status via a web page, greatly facilitating maintenance work. However, it is important to use industrial-grade cables, as regular network cables are prone to interference.

4

Application of Modbus Protocol

Modbus can be considered the “big brother” of industrial communication, with a simple structure and ease of use, particularly suitable for small systems.

Communication Methods

• RTU mode (serial communication)
• TCP mode (Ethernet communication)
• Baud rate is generally set to 9600 or 19200
• Supports up to 247 slaves

Data Organization

• 00001-09999: Output coils
• 10001-19999: Input contacts
• 40001-49999: Holding registers
• 30001-39999: Input registers

Program Example

// Use MOVE_BLK instruction to read Modbus registers
MOVE_BLK(
    SRC := MW100,   // Source data area
    COUNT := 10,    // Data length
    DEST := DB1.DBW0   // Destination data area
);

5

Troubleshooting Common Issues

1. Communication interruption issues

• Check network connections and termination resistors
• Confirm address settings are correct
• Verify communication parameter compatibility
• Observe status LED indicators

1. Data anomaly issues

• Check if data types match
• Confirm byte order settings
• Verify if data area is out of bounds

1. Stability issues

• Use shielded cables
• Avoid running parallel to strong electrical lines
• Set reasonable timeout periods
• Regularly back up communication configurations

6

Practical Recommendations

Selection Recommendations:

• Prioritize Modbus for small systems
• Use PROFINET for high-speed real-time requirements
• Use PROFIBUS for high anti-interference requirements

Tuning Tips:

1. Use network analyzers to monitor communication
2. Configure communication parameters gradually
3. Keep records of communication data
4. Establish emergency response plans

Safety Precautions:

1. Keep communication cables away from strong electrical lines
2. Regularly check terminal connections for looseness
3. Set communication timeout protection
4. Ensure lightning protection and grounding

Engineering Implementation Recommendations:

1. Leave expansion space in communication planning
2. Create detailed configuration record documents
3. Plan IP addresses and station numbers reasonably
4. Establish a list of device communication parameters

Mastering these communication protocols is like opening a door to industrial automation. In practical applications, it is essential to choose the appropriate communication method based on specific needs while paying attention to details and safety issues. Through continuous practice and summarization, I believe you will soon be able to skillfully apply these technologies.

Previous Reviews

Siemens PLC System Performance Optimization Guide, Solving Issues like Lagging and Slow Response

The Role of Siemens PLC in Digital Transformation, Prospects for New Technology Applications in Smart Manufacturing

[Practical Skills] Application Techniques of Siemens PLC in Motion Control, Complete Guide to Motor Control and Positioning Functions