Research And Implementation Of Process-oriented Machining CAN Control Network Application Layer Protocol

With the rapid development of system control, computer, digital communication and other technology, network that controlling industrial automation has become inevitable. With its short data frame, low cost, high real-time, good fault-tolerance and reliability, strong anti-interference ability, multi-master work, the CAN bus becomes the most promising control network. CAN bus protocol is open, it only specify the physical layer and the data link layer, but does not define the application layer. So it takes a long time to realize application development and to overcome technical difficulties. For the processing field, specifying CAN bus data frame coding, defining the communication patterns and mechanisms to achieve CAN controls network communications platform, are always the subject of applied research.In this paper, the CAN bus and its main characteristics were described, the theory of communication protocols and typical application layer protocols were analized, the structure model of processing control system were defined, the rule and the characteristic of processing control system and the corresponding communication message types were also summarized. Then standard data frame identifier and data field encoding were defined according to the CAN2.0A technical specification. The data communication and network management model were standardized. The process-oriented machining of CAN bus application layer protocol(referred to as Pro CAN) was proposed. The coding efficiency and communication delay of the Pro CAN protocol were analyzed; using OPNET modeling and simulation tools to verify the validity of Pro CAN protocol. In the hardware design of integrated communications platform, design and implementation network communication software based on Pro CAN, and to be function tested.The hardware platform of network communication consists of PC operating station, USB-CAN adapter, CAN interface and on-site control nodes and other layers, of which CAN interface consists of a microcontroller STC90C516RD+, CAN controller SJA1000 and CAN driver PCA82C250. Network communication software contains two parts: PC operating station communication software and on-site control nodes communication software. The PC operating station communication software includes modules that realize CAN adapter initialization, message sending, receiving, display and exception handling. The control node communication software includes modules that realize SJA1000 initialization, CAN messages sending and receiving.