Study On The CAN Protocol In The Fieldbus Communication Environment

Fieldbus is a new way of communication in factory field level area. It has beencalled a beginning of new control technology age. CAN(Controller Area Network) busis one of fieldbus international standard that is most early established and widely usedin all over the world. It has the characteristic of low cost,fast speed,high real-time andreliability. It is convenience for customer to design and extend their own applications bythe opening protocol of CAN bus. In modern industry control system, the application of the digital distributed controlsystem based on fieldbus has made it possible of incorporating the management andcontrol. However,the new problem in intelligent control system is how to improve theflexibility of the system efficiently so that the control and adjustment can be timelyexecuted with the requirement of the real-time data transmission . The development of fieldbus and the protocol content of CAN are first presentedin this paper, and the circumstance and performanceof real-time communication inmodern industry control system are discussed. On a basis of the research founded byShaanxi project "Design of smart electrical actuator based on fieldbus"and Xi'an project"design of intelligent measurement and control node based on CAN", the followingproblems are studied: flexible control and real-time communication in modern factoryautomation; the model and protocol in CAN circumstance, including several popularCAN highlayer protocol such as CANopen, DevicNet; time trigger and event triggerschedule in CAN;design of intelligent CAN node based on 80C51MCU. The softdesign of CAN communication with the time trigger schedule improve the CAN node'sflexibility and reliability. The further work to be done is studying the better method ofonline event trigger service and complicated message schedule under the critical timeconstrain by FPGA or DSP.