Development Of National Standard Draft For Modbus Protocol Test Specification And Test System

Fieldbus is one of the hot ports of automation field in modern time. Modbus protocol has become an industrial standard in use which is a technology supporting distributed and real-time control effectively. The application of Modbus protocol over serial link is therefore becoming more and more widespread. As a new problem posed by that, bad interoperability between modbus devices over serial link has restrained the development of modbus technology seriously.Based on deeply research on fieldbus protocol test and guided by practical experience in industry,this paper proposes a formula for test of modbus protocol over serial link, draws up a national standard draft of modbus protocol test specification over serial link, develops a corresponding test system for modbus device over serial link.First,accroding to introduction of fieldbus technology,on the basis of analysis of protocol test,this paper proposes a formula including basic framework and test procedure for test of modbus protocol over serial link. This test is performed at three levels of physical,data link and application.Second,based on a mainframe made by formula of test of modbus protocol over serial link, draws up a national standard draft of modbus protocol test specification over serial linkoThird,this paper develops test system for modbus protocol over serial link,which could make conformance test and interoperability for modbus devices over serial link.This paper describe design and implementation of the system composed of hardware environment and test software.The design of hardware environment constructs a test platform,which sets up a host-sub system.As the central component of test system,test softsware is on the basis of Win32 application .After making reserch for window application,windows serial communications,it focus on the design and implement of software modules and provides flow charts,code, result of each module of the software.At last, this paper introduce some experiments constructed in test system.After that test,the system achieved expected design requirements basically.