Modbus TCP and Modbus RTU: In-depth analysis of the differences between the two

Modbus is a widely used industrial communication protocol for connecting industrial electronic devices.The Modbus protocol has two main transmission modes: Modbus TCP and Modbus RTU.Although they are all based on the Modbus core protocol, they have some key differences in implementation and application.This paper will compare and analyze these two models in detail.

1. Concept and essence

Modbus RTU and Modbus TCP are both part of the Modbus protocol, and their cores are based on Modbus register addresses for data exchange.Modbus protocol defines the structure of message and data, command and response mode, and adopts master-slave (Maser/Slave) communication mode.

2. Communication mode

Modbus RTU is mainly based on asynchronous serial transmission, and the commonly used interfaces are RS-232, RS-485/422, etc.This type of communication is widely used in both wired and wireless environments.Modbus TCP, on the other hand, is based on an Ethernet connection, which uses the TCP protocol in the TCP/IP suite.

3. Data transmission

The Modbus RTU transmits data directly as binary data, which is determined by the data length (two bytes,Represents the number of registers) and the data body (M times 2 bytes).Modbus TCP, on the other hand, converts each byte of binary data into a fixed two-digit hexadecimal string, which is then concatenated together in turn.Data is transmitted in the form of TCP code.

4. Verification mode

Because Modbus RTU uses serial communication, it needs to verify the data to ensure the accuracy of the data.In Modbus RTUs, LRC (Longitudinal Redundancy Check) or 16-bit CRC (Cyclic Redundancy Check) are commonly used in addition to parity.Modbus TCP, on the other hand, does not require additional checks because the TCP protocol itself is a connection-oriented and reliable protocol.

5. Application scenario

Modbus RTU is widely used in various industrial field devices because of its simplicity, reliability and cost-effectiveness.Modbus TCP is more used in industrial automation systems based on Ethernet.

Although both Modbus TCP and Modbus RTU are important parts of the Modbus protocol,However, there are obvious differences between them in terms of implementation, communication interface, data transmission and verification.Choosing the appropriate transmission mode depends on the specific application scenarios and requirements.For example, Modbus RTU may be a better choice for applications requiring long-distance transmission or wireless transmission;Modbus TCP is more suitable for Ethernet-based industrial automation systems.

Hopefully this article will help you better understand and differentiate the difference between Modbus TCP and Modbus RTU.In the field of industrial Internet of Things, it is very important to have a deep understanding of protocols and communication methods.It helps us design and implement industrial automation solutions more effectively.