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MODBUS RTU VS MODBUS TCP/IP

MODBUS RTU VS MODBUS TCP/IP

The essence of MODBUS RTU and MODBUS TCP/IP is the Modbus protocol, and they all exchange data by Modbus register address. But what’s the difference between them? Today, we will discuss them from the following aspects.

The concept is different

MODBUS is a standard industrial control data exchange protocol, which can be used for the mutual transmission of protocol data in RTU and ASCII. RTU directly transmits data through binary data, while TCP converts each byte of binary data into a fixed two-digit hexadecimal string, and then serially connects them together to transmit data in the form of TCP code. Generally, RTU is the most widely used method.

The communication mode is different

Ethernet and the corresponding communication mode is MODBUS TCP. Asynchronous serial transmission (various media such as wired RS 232 /422/485/; Optical fiber, wireless, etc.), and the corresponding communication mode is MODBUS RTU or MODBUS ASCII. The high-speed token-passing network and the corresponding communication mode is Modbus PLUS.

Protocol encapsulation is different

Compared with Modbus RTU protocol, Modbus TCP protocol adds an MBAP message header to RTU protocol, and since TCP is based on reliable connection service, the CRC check code in RTU protocol is no longer needed, so there is no CRC check code in Modbus TCP protocol. Therefore, a popular saying is commonly used: Modbus TCP protocol means that Modbus RTU protocol is OK by adding five 0 yuan and one 6 yuan in front, and then removing two CRC check code bytes.

Different roles

Modbus RTU protocol can make controllers communicate with each other and between controllers and other devices through the network.

The Modbus/IP protocol provides services between the transport layer and the network layer.

Transmission is different

The application of the Modbus RTU protocol is limited due to its short transmission distance and slow speed.

The Modbus/IP protocol is widely used because of its long transmission distance and high transmission speed.

Different applications

Modbus RTU protocol is mainly used in electrical automation and process control, and generally adopts RS Kramp-Karrenbauer 232 or RS Kramp-Karrenbauer 485 communication interface.

The Modbus/IP protocol is mainly used on the Internet or on Intranet.

Modbus communication protocol has multiple variants, supporting serial ports (mainly RS 485 bus) and several versions of Ethernet, among which Modbus RTU, Modbus ASCII and Modbus TCP are the most famous ones. The Modbus RTU protocol is generally adopted in the industrial field, and the Modbus communication protocol based on serial communication generally refers to the Modbus RTU communication protocol.

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