Design And Research Of CAN-USB Host-Slave Communication Adapter

As one kind of field bus, CAN is widely applied in many areas for its great features of distributed control and real-time capability, such as industrial production, automotive electronics, robots and aerospace. In the process of design, development and debugging, monitoring and maintenance of CAN bus system, it is necessary to connect it to the computer for online monitoring, test, data analysis, performance verification and troubleshooting using its powerful analysis and processing capability. On the other hand, for many CAN bus systems which need long-term running, such as the monitoring of field geological condition, data needs to be saved in mass storage facilities for data analysis and data mining. In such conditions, saving the data to the computer on-line will be very inconvenient, so there is a need for the off-line storage function.In the traditional methods of connecting the CAN bus and the computer, using the RS232interface can no longer meet the increasingly high speed requirements and has been gradually eliminated. The method of using the acquisition cards based on PCI and ISA has the disadvantages of hard to install, poor portability and scalability, high price. USB interface has been widely used and becomes one of the essential interfaces for computer peripherals because of its good scalability, supporting hot plug, low cost, convenience to use, high transfer rate and great portability. The method of using USB interface for CAN communication is gradually developing. The USB-CAN adapter used now can only support the USB slave mode. It just receives and transmits the CAN packets and is hard to configure with low efficiency. It does not support USB host mode and can’t save the data to storage facilities. The price is high too. As a result, the market needs a adapter which supports both host and slave mode and can save data off-line with high efficiency and low cost.The paper introduces the status and needs of the CAN bus communication with the computer, compares the advantages and disadvantages of various methods, studies the standard protocol of USB and CAN, and put forward a scheme of CAN adapter based on USB interface and supporting host and slave mode. The adapter uses STC89C54RD+as the microcontroller, CH375as the USB interface chip and SJA1000as the CAN controller chip. In USB slave mode, the adapter can handle the bidirectional communication between CAN bus and the computer. The computer can send orders to configure the lower machine, and can receive, display and store the CAN bus data. In USB host mode, the adapter can store the CAN bus data to the memory of the USB interface in a file. The paper describes the overall scheme of the adapter, the division of module and the selection of devices in details, designs the hardware and software of lower machine and the application program of upper machine. The adapter integrates the advantages of USB and CAN, has low cost, good scalability, strong stability and wide range of applications. It has great application value and popularization value.