Simple Modbus Data Source Tool implementation (1) WinForm and modbuswinform

Simple Modbus Data Source Tool implementation (1) WinForm and modbuswinform

This is a process of self-review for learning C # And Winform. It is used to find out the shortcomings and to promote continuous learning.

After graduating from college communication, I joined an electric power technology company engaged in software development. I mainly used Delphi to develop the upper computer of the electric power communication protocol. Because the upper computer needs to communicate with the lower computer for testing, but in fact there are not so many ready-made devices for you to borrow for debugging, and the company is slowly starting to implement C #/WPF for some customized software, so I want to learn about C #, but now there is also a demand -- it is difficult to debug the host computer program, so I will start with the winform program that is the easiest to start, gradually deepen your understanding of the C # language. As a result, we plan to create a data source tool with common Modbus protocol, so we have this article.

 

1. Introduction to Modbus protocol

{From Baidu encyclopedia}

Modbus was invented in 1979 by Modicon (now a brand of Schneider Electric) and is the world's first bus protocol truly used in industrial field. ModBus network is an industrial communication system, which is composed of programmable controllers with smart terminals and computers connected through public lines or local dedicated lines. The system structure includes both hardware and software. It can be applied to various data collection and process monitoring. The ModBus network only has one host, and all communications are sent by him. The network can support as many as 247 remote slave controllers, but the actual number of slaves is determined by the communication device used. With this system, each PC can exchange information with the central host without affecting each PC to execute its own control tasks. Ii. Modbus protocol features {from Baidu Baike} (1) standard and open. Users can use Modbus protocol free of charge and rest assured. No license fee is required or intellectual property rights are infringed. Currently, more than 400 manufacturers support Modbus, and more than 600 Modbus products are supported. (2) Modbus can support a variety of electrical interfaces, such as RS-232, RS-485, etc., can also be transferred in a variety of media, such as twisted pair wire, optical fiber, wireless and so on. (3) the Modbus frame format is simple, compact, and easy to understand. Users are easy to use and vendor development is simple. Iii. Description of Modbus Packet Structure

Each Modbus Packet consists of the following parts:

(1) Address domain

(2) function code domain

(3) data domains

(4) verification domain

　　

Address field: 0 ~ 247,0 is generally used as the broadcast address, 1 ~ 247 is the address number used by the device (lower computer.

Function Code: used to confirm the specific functions of the packet. (Common code 03 and 10)

0x03	Read register
0x10	Write register
0x05	Remote Control

Data field: the length of the Modbus data field varies depending on its specific functions. Verification domain: CRC16 verification method, two bytes in length. Iv. Serial Port and Ethernet Modbus Packet serial port: ModbusRTU Ethernet: ModbusRTU; Message format: [Transaction metadata identifier (2 bytes)] + [Protocol identifier (2 bytes)] + [length (2 bytes)] + ModbusRTU-CRC Check (2 bytes) All in all, ModbusTCP has 6 more packet headers than ModbusRTU, the CRC check with two bytes at the end is missing. The following mainly describes the ModbusRTU: 0x03 code.

Read register data packet format		Response format
Slave site address	1 byte	Slave site address	1 byte
Function Code	1 byte	Function Code	1 byte
High starting address of register	1 byte	Bytes n	1 byte
Low starting address of register	1 byte	Data1 high	1 byte
High number of registers	1 byte	Data1 low position	1 byte
Low register count	1 byte	......
		Datan/2 high	1 byte
		Datan/2 low	1 byte
Low CRC verification code	1 byte	CRC low	1 byte
High CRC verification code	1 byte	High CRC	1 byte

0x10 code

Write register data packet format		Response format
Slave site address	1 byte	Slave site address	1 byte
Function Code	1 byte	Function Code	1 byte
High starting address of register	1 byte	High starting address of register	1 byte
Low starting address of register	1 byte	Low starting address of register	1 byte
High number of registers	1 byte	High number of registers	1 byte
Low register count	1 byte	Low register count	1 byte
Bytes (n)	1 byte	Low CRC verification code	1 byte
Data1 high	1 byte	High CRC verification code	1 byte
Data1 low position	1 byte
......
Data (n/2) high	1 byte
Data (n/2) low	1 byte
Low CRC verification code	1 byte
High CRC verification code	1 byte

0x05 code

Request format		Response format
Slave site address	0x11	Slave site address	0x11
Function Code	0x05	Function Code	0x05
Preset address height	0x23	Preset address height	0x23
Low preset address	0 x 8C	Low preset address	0 x 8C
Set Data height	0 x FF	Set Data height	0 x FF
Set low data	0x00	Set low data	0x00
Low CRC verification code	44	Low CRC verification code	44
High CRC verification code	C5	High CRC verification code	C5