Automatic MODBUS-RTU communication baud rate matching method

Abstract

The invention discloses an automatic MODBUS-RTU communication baud rate matching method. The method is achieved through the steps of firstly, setting the baud rate of a serial port as the default baud rate when a slave station is powered on, waiting for receiving a serial port message on a bus, resetting the baud rate of the serial port as the agreed next baud rate of a master station and the slave station if the messages unceasingly received five times are wrong messages till a correct serial port message is received, and achieving communication with the master station with the baud rate; secondly, changing the baud rate of the master station under the normal communication condition, detecting whether the received message on the bus is correct or not in real time through the slave station, repeatedly executing the baud rate matching process if the wrong messages are unceasingly received five times till the correct message is received, judging the data format based on a MODBUS communication protocol according to whether the message received by the slave station is correct or not, and conducting verification, wherein a CRC verification code and the length of the whole message are mainly verified. By means of the method, the baud rate of the master station and the baud rate of the slave station can be automatically matched without changing bus communication or all devices arranged on the bus.

Description

technical field [0001] The invention relates to the field of industrial automatic control, in particular to the automatic matching of MODBUS-RTU communication baud rate. Background technique [0002] The MODBUS-RTU protocol is an open and widely used serial communication protocol originally developed by Modicon for its programmable controllers and industrial automation systems. It is widely used to transmit digital and analog I / O and Used when registering data, this protocol defines a message structure that controllers can recognize and use, regardless of the network through which they communicate. It describes the process of a controller requesting access to other devices, how to respond to requests from other devices, and how to detect and log errors. It formulates the public format of the message domain structure and content. On the RS-485 bus, most of them adopt the master-slave communication mode, one host, and connect multiple slave stations. The communication betwee...

AI Technical Summary

Problems solved by technology

[0003] For RS-485 bus communication, the communication baud rate of devices connected to the same bus must be the same. The existing RS-485 communication baud rate settings are all set through dial-up development, software or other methods, and need to be changed. The baud rate of the bus communication must be set for each device on the bus. There may be dozens of devices on a bus, and the distance between each device is tens to hundreds of meters, possibly thousands of meters. The whole system runs In the future, if the communication is unstable and it is necessary to reduce the communication baud rate to enhance the stability of the communication, it is necessary to stop the operation of the entire bus device, set it manually by dialing code development, software or other methods, and restart it after setting For the devices on the entire bus, this process takes tens of minutes to several hours, 1. Increases the maintenance labor cost of the entire system; 2. Stopping the operation of the entire bus device for tens of minutes to several hours will bring serious consequences to the entire system

Images