Research Of Network Instrument Based On The DeviceNet

The field bus is an advanced industrial control technology, it connects all kinds of intelligent instruments in the industrial field with the monitor in the control room, and they compose the field bus control system (FCS).The FCS usually exits two kinds of node:master station and slave station. The master station has a strong functions, it takes charge of the monitor and congfiguration of all slave stations and displays all kinds of information by LCD panel and so on. The slave station relatively has a simple function compare to the master station; it usually has a single task, for example, temperature sampling.The master station is the main object we researched in this thesis, it is developed by CAN Bus, the CAN Bus is thunk as one of the most promising field bus, it can make sure the real-time and correctness of transmiting data, but it only defines the physical layer and the data link layer, the application layer is defined by the developer according to actual situation. So, the other main task in this theis is to define and implement the protocol of application layer.Taking into account that the master station has strong functions and takes charge of many tasks, the traditional C51 microcontroller can not meet the requirements in operational speed and addressable range. After analying, we select the S3C44B0X microcontroller which has a good cost-effective as the control unit of the master station. Its kernal is ARM7TDMI, can offer 3 pipelines of instruction and a lot of embedded peripherals, its addressable range is high to 256MB. But it does not offer embedded CAN controller, can not implement CAN protocol, we have to plug-in a seperate one. Because its address lines and data lines separately work and it offers an embedded SIO controller (compatible SPI), we deside to select the MCP2515 which has a SPI interface as the CAN controller, its SPI baudrate is high to 10Mbps, has not any limit to CAN baudrate (the most speed of CAN baudrate is 1Mbps).Finishing the hardware design, we have to define and implement the protocol of application layer, in this process; we refer to the DeviceNet protocol. It is a protocol of application layer based on CAN protocol. So far, it has been relatively perfect and sound. Especially, it has a good value in the definition of message format, physical type, physical unit and data type.