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This article mainly shows you "what is the difference between Modbus TCP and Modbus RTU", the content is easy to understand, clear, hope to help you solve your doubts, the following let the editor lead you to study and learn "what is the difference between Modbus TCP and Modbus RTU" this article.

The Modbus protocol is a messaging structure developed by Modicon. It is used to establish master-slave / client-server communication between devices. Modbus has many protocol options. But the two most commonly used are Modbus RTU (remote terminal unit), serial (RS-232 or RS-485) protocol or Modbus (TCP / IP) transmission control protocol and Internet protocol. What's the difference between the two? Although the two protocols are similar, cost and speed make a difference.

Modicon introduced the Modbus agreement to the market in 1979. The Modbus RTU pattern is the most common implementation, but Modbus TCP / IP is gaining popularity and is ready to go beyond it. In order to make Modbus enter the 21st century, the open Modbus TCP / IP specification was developed in 1999. Modbus is an open standard and a widely used network protocol in industrial manufacturing environment. This is a universal link implemented by hundreds of vendors that can be integrated into thousands of different manufacturing devices to transfer discrete / analog I / O and register data between control devices. MODBUS communication is always initiated by the master node to the slave node. The slave nodes do not communicate with each other without receiving the request from the master node, and the data is not transmitted.

Coils starting at 00001 correspond to on / off binary outputs, such as relays.

Input bits starting at 10001 correspond to binary input (read-only).

The input register, which starts at 30001, corresponds to analog input (read-only).

The hold register, which starts at 40001, corresponds to the ability to change the simulation parameters.

Instead, the Modbus RTU pattern is the most common implementation, using binary encoding and CRC error checking. The RTU protocol is an efficient binary protocol in which each octet in a message contains two four-bit hexadecimal characters. Each message must be sent as a continuous stream. The format of each byte (11 bits) in RTU mode is: coding system: 8 bits binary, each byte: 1 start bit, 8 data bits, the least significant bit is sent first, 1 bit is used for parity completion, 1 stop bit. MODBUS RTU packets are used only to send data. They do not have the function of sending parameters, such as point name, resolution, unit and so on. The standard MODBUS RTU node address is 1-254, where 0 is reserved for broadcast messages and only for writes. MODBUS on a serial line system may use a different physical interface (RS485,RS232). The TIA / EIA-485 (RS485) two-wire interface is the most common. As an additional option, you can also implement the RS485 four-wire interface. The RS485-MODBUS configuration without a repeater has a trunk cable through which the device (daisy chain) is connected directly. Backbone cables (also known as "buses") vary in length, but both ends must be connected to the line terminal. Repeaters can also be used between multiple RS485-MODBUS. The length of the beginning and end of the trunk cable must be limited. The maximum length depends on the baud rate, the cable (specification, capacitance or characteristic impedance), the number of loads on the daisy chain and the network configuration (2 or 4 wires). The typical cable length of this bus connection is 1000m and the typical baud rate is 9600 bps. Good cable selection, at least 22 wire gauges

Modbus TCP / IP is simply a Modbus RTU protocol with a TCP interface running on Ethernet. With Ethernet, you can combine a universal, scalable global physical network (Ethernet) with a common network standard (TCP / IP) and a vendor-independent data representation, Modbus. The protocol provides a truly open, accessible network that allows the exchange of binary blocks between devices. For any device that supports TCP / IP sockets, each device has available switches and cables, which is easy to implement. It is fully compatible with any Ethernet infrastructure that customers may have installed.

Ethernet is certainly much faster and easier to troubleshoot. However, you may not want to use Ethernet for Modbus communications. Maybe it's too soon. TCP / IP is a common transport protocol on Internet and a set of layered protocols that provide a reliable data transfer mechanism between machines. Ethernet has become the standard for many systems, so it is not surprising that it has also become one of the standards for factory networking. Because Ethernet technology has been around for many years, it has developed to such an extent that the cost of implementing this network solution has become affordable.

Ethernet devices will become faster, but for many Modbus devices, speed is not entirely necessary. All these level sensors, temperature sensors, Flowmeters and other transmitters do not need to report data very quickly. It is necessary to report data every few seconds. Throughput is not a good reason to use RTU over Ethernet. The most basic difference between MODBUS RTU and MODBUS TCP / IP is that MODBUS TCP / IP runs on the physical layer of Ethernet, while Modbus RTU is a serial level protocol. Modbus TCP / IP also uses 6-byte headers to allow routing. You will encounter a lot of problems trying to make the RS485 network work properly. Compared with Ethernet devices, you have to deal with wire terminal issues, network terminal issues, and more configuration issues. But overall, do you use Modbus RTU devices over Modbus TCP? Modbus TCP / IP is just the Modbus RTU protocol with an TCP interface running on Ethernet. Therefore, if you want to get data quickly and want to enter the 21st century, then Modbus TCP / IP is the only way.

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