Research Of Modbus Protocoland Design Of The Experiment System

The Fieldbus technique has being one of the central points in the domain of industry control at present. Modbus protocol has been applied widely in the field of industry automation and intelligent apparatus and meters because of its excellent characters in protocol efficiency, methods to operate, and cost efficiency. However, the developing of Modbus in China always limits to junior application and manufactures, but lacks in research on core of Modbus theory and technique.This paper takes the performance analysis for Modbus RTU protocol base on the research of Modbus protocol, also combining the Modbus specification of Application Layer and Data Link Layer in the analysis. It takes the quantitatively analysis for performance indexes according to performance evaluation indexes of Fieldbus, such as throughput, efficiency of Modbus protocol and network. Furthermore, it evalues the advantage and disadvantage in consideration of the real-time performance and reliability relevant to each layer of Modbus protocol. In the end, I design a Modbus experiment system, which could afford experiment projects base on chief Modbus theory and technique. It solves some pivotal problem such as space time between characters on bus, interfere and CRC, etc.The design process conforms to modularization principle. The methodology I use is dividing system into nodes, and then into circuit units, accordingly, experiment flow is divided into main then to function element program. It adduces the structured chart and circuit units for H/W, and provides several representative program flow diagrams for S/W. Finally, it demonstrates the Modbus protocol and experiment result with some waveforms and data.To summarize, analysis in this paper is exhaustive and specific, and the experiment system and items designed is representative, the node's communication mechanism complys with the Modbus protocol absolutely. It could acquire and control remote digital parameter, or analog ones by the instrumentality of additional A/D and D/A modules. It's conduced to comprehend through the technology of Modbus and beseem to develop other fieldbus products as a reference.