| CAN line is a live one with an international standard and higher performance-cost ratio, which plays an important role in the automatic controlled field nowadays .The bus control system on-the-spot is both an opening communication network and a complete distributed control system. As a tie of intellectual equipment, it makes the intellectual equipment which is locked with the bus as the nodal network for the network system, and forms the automated system further so as to realize the comprehensive automation function integrated with basic control, compensative calculation, parameter revision, alarm, display, control, optimization and management and control. It is a comprehensive technology concerned with embedded system, control, computer, digital communication and network. The size of live CAN belongs to LAN, bus architecture that is simple but it can meet demands of scene. The information frame that is transmitted is short and small; it requires real-time and dependability highly (Few network structure levels and short frame help improve real-time and reduce probability of interference). But there are much interfered factors on the scene, some are very strong and too sudden. All these determine the bus on the spot must have its own distinct characteristics in the field of studying hardware. Direct against the hardware circuit with intelligence nodal based on PIC18F258 of the CAN controllers and the software structure, it is the innovation of this text using the USB interface to carry out the scheme of the CAN bus network that connects with computer. It is the fact that a lot of scholars and experts pay close attention to the composition of systematic hardware and design method of firmware. PIC18F258 is a high-performance one-chip computer with the CAN bus interface; it needn't to expand the CAN interface outside again; only adding a bus driving chip is all right, which helps communication debug and improves systematic anti-interference ability. It adopts reduction of simplifying instruction collection (RISC), the Harvard bus structure, the way of the assembly line collecting the instructions, which has the characteristics such as application, low price, small order, good anti-interference, low-energy consumption, high speed, small volume and strong function. Meanwhile, it has improved such functions as the A/D converters, the storage of inner EEPROM, relatively output, catching input, PWM output, IC bus and SPI bus interface circuit, asynchronous serial communication interface circuit (USART), simulation voltage comparator and readable / writable FLASH procedure memory unit. PDIUSBD12 is USB interface devices at full speed, and one of most usable chips at the USB 1.1 agreement equipment end, and full-speed USB devices have the collateral bus and local DMA transmitting ability. Chips are integrated with high-performance USB interface devices, SIET, FIFO storage, transceiver and voltage adjuster, which can realize the collateral interface at a high speed with any outside tiny controller / microprocessor (2MB/s). The collateral interface of PDIUSBD12 and the current collateral interface have the same characteristics that use easily and run fast. Combining the advantages of USB and CAN buses, use USB interface to expand the control and management of CAN buses; through great performance of PC machine, monitor and control users systems of the CAN bus, collect each nodal information on the CAN buses, and send controlling instructions to each node through the CAN buses to improve the functions of control management in industrial use of the CAN buses, and expand the ranges of application of CAN buses at the same time. |
