Study And Development Of Protocol Conformance Test System For Modbus Serial Line

Fieldbus is having been regarded as local area network of computer in automatization domain during these years. Nowadays, the Modbus is widely used in many factory automatization domain for its advancement,open,mature, and adopted by many manufacturers. But at the same time, some relevant problems are following one by one: the Modbus device coming from different manufactures are more and more,although all of them abide by Modbus protocol, every development engineer comprehends the protocol differently ,therefore the devices can't work successfully together when the whole system is integrated.Modbus communication has three forms: serial line,TCP/IP and Modbus PLUS, and the first one is the paper's topic. The paper draws the Modbus serial line protocol conformance test specification (Wd working draft) and develops the relevant system. So it can implement the conformance and interoperation test for devices based on Modbus serial line.First, the formulation of Modbus serial line protocol conformance test specification is the base of this research work. The specification is finished by study MODBUS APPLICATION PROTOCOL SPECIFICATION, by collectings comparing,practicing much device technology information and experience from veteran experts.Second, the paper designs the frame and flow of Modbus protocol conformance test according to Modbus serial line protocol conformance test specification and test cases of other fieldbus, and then develops the test system.The hardware environment is the test platform which is built as a master/slave system based on RS485 transmission, especially the test detail for physics layer and data link layer is an innovation specially for serial line. Software environment is an internet application. The paper expresses the thoughts and implement course, such as flow charts,part of important codes and results for every module. The basic function of the software is comparatively complete in the development. For example: negation test, the exception reason according to the exception code in response frame can be judged, so the fault can be solved purposefully.At last, this paper introduces some experiments constructed in the test system. After that test, the system achieved expected design requirements.