The Design of CAN Bus Communication System Based on MCP2515 and S3C2440 Jinmei Liu, Junhong Wang, Donghui Sun

Transcription

1 Advanced Materials Research Online: ISSN: , Vol. 933, pp doi: / Trans Tech Publications, Switzerland The Design of CAN Bus Communication System Based on MCP2515 and S3C2440 Jinmei Liu, Junhong Wang, Donghui Sun Deportment of Electrical Engineering, North China Institute of Astronautic Engineering, Langfang, China Keywords: Linux; S3C2440X; MCP2515; CAN BUS; SPI Interface Abstract. CAN bus was widely used in embedded system development, but most embedded processors without CAN bus controller, need to extend external CAN bus interface through external bus. In order to send and receive the CAN bus data by S3C2440 chip, interface function of S3C2440 was extended by MCP2515 chip in the paper, which was used the SPI interface to extend CAN bus interface. The design of CAN bus hardware interface was described in the paper. The design of CAN device drive program on the embedded Linux operating system was specified in detail. Introduction At present, because of CAN bus s low cost, high reliability, strong anti-interference capability, convenient connection and communication speed advantages, it is widely applied in many fields of industrial automation, control system, medical equipment etc.. The most widely used CAN controller chip for the Philips Corporation's SJA1000, has the advantages of low cost, high reliability, support for long distance communication features, but the address bus and data bus interface time division multiplexing often leads to low efficiency, the number of receive and transmit buffer is too small. Microchip MCP2515 is an independent CAN protocol controller, fully support the CANV2.0B specification, SPI interface with industry standard. CAN bus structure CAN bus is divided into the data link layer, physical layer, which function is accomplished by CAN controller. The data link layer comprises a logical link control layer (LLC) and media access control layer (MAC). Logical link control layer features include: frame receiving filter, overload notification and recovery management. The media access control layer including sending part and receiving part, the main function for the information package to send, send media access management, receiving media access management, receiving information uninstall. The data link layer will send the data package, including error check bits, the data link protocol control information, and additional information such as data frame composed of markers, sent from the physical channel out; after receiving the data frame, then the additional information is removed, the communication data. In the process of communication, and both parties should check the control information added to discrimination, and make the appropriate treatment, so as to realize the control, error detection rate in the process of data transmission, to ensure correct data transmission. The physical layer is the realization of the hardware circuit, provides the communication medium mechanical, electrical, function and regulation characteristics. It includes physical signaling (PLS), the physical media attachment (PMA) and media interface (MDI) layer. The main function of the realization of information synchronization, bus transmit/receive circuit and mechanical and electrical interface. The physical layer specifies the level of CAN bus as the two states: "hidden" (logic 1) and "dominant" (representation logic 0); and also provides the realization of "and" logical functions through the specific circuit. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-04/03/16,02:38:16)

2 Advanced Materials Research Vol CAN communication protocol has four kinds of different frame formats, namely remote frame, data frame, overload frame and frame error. Among them: the data frame used for transmitting data; remote frame for application data; a global signal error frame by local detects an error condition; overload frame for delay time extended frame sequence. Overall System design of CAN bus TQ2440 development board based on CAN bus communication system, using S3C2440 processor, processor based on ARM920T core, the frequency is 180 MHz, performance can reach 200MIPS; the highest frequency is 500MHz. Using the SPI interface of the general GPIO, extends the CAN bus interface. Extended so we choose SPI interface and S3C2440 MCP2515 multiple CAN bus interface. The principle of realizing the system is shown in figure 1. The software platform of Redhat9.0 cross compiler environment, cross compiler used for the cross compiler technology of EABI (the highest version), the development of Linux application development QT PC machine, and the porting of QT to arm-linux system. Fig.1 System implementation principle CAN bus hardware interface design Bus of MCP2515 is adopted to separate address and data, CAN-bus control chip with independent CAN controller, fully compliant with the 2.0B specification of CAN-bus, and with a SPI interface is compatible with the industry standard. The device is capable of sending and receiving standard and extended data frames and remote frame. MCP2515 with 2 acceptance mask register and 6 acceptance filter register, can filter out don't message, reduces the control overhead. A variety of MCP2515 mode, can be flexibly applied to the application system, through the monitoring mode, can realize the automatic baud rate detection in CAN network. MCP2551 is the interface between CAN controller and the physical bus, it can enhance the bus drive capability, which increasing the communication distance of CAN bus nodes and makes it possible to mount more on a bus. MCU and MCP2515 are communicated by the high speed SPI interface. Compared with the traditional controller, it has the ability of frame interrupt, shielding and filtering, frame priority flexible setting characteristics and high data throughput rate, low price and less MCU pins etc. So the

3 518 Manufacture Engineering, Quality and Production System III system is used as the CAN protocol controller and the physical bus interface. The initialization of MCP2515 includes the configuration of the configuration register, shielding and filtering registers, interrupt and control registers. The hardware design of CAN node has two kinds: one kind is CAN controller with microprocessor intelligent node independent, independent CAN controller with 82C200, SJA1000, MCP2515 and Intel82526/82527; the other is the micro structure of the intelligent controller by on-chip with CAN, such as P80C592 and C167CR etc. This system uses MCP2515 independent CAN controller as CAN controller, MCP2551 bus transceiver. The CAN bus interface hardware circuit as shown in figure 2. Fig.2 CAN Bus interface circuit design CAN bus transceiver connected through MCP2551 and physical line, can increase the communication distance, improving system transient anti-interference ability, reducing radio frequency interference. 6N137 is a high speed optical coupler, which improves the anti-interference ability of the system. Increase the photoelectric coupler 6N137 between MCP2515 and CAN bus transceiver MCP2551, the electrical complete isolation and independent nodes, using two independent power supplies, further the complete separation of power. Both ends of the CAN bus of the increase in resistance of the two 120 K, can effectively improve the anti-interference and reliability of data communication. Software Design The CAN bus interface software CAN MCP2515 controller provides a convenient "channel" for the application layer access, the "channel" shielding the implementation details of CAN controller, the application layer communication oriented is transparent. The interface by SPI communication interface to achieve the CAN controller operation. The mutual relation between them is shown in Figure 3. Fig.3 CAN software interface

4 Advanced Materials Research Vol The driver write S3C2440 as the main controller, through the SPI interface, using MCP2515 controller to extend CAN bus interface. Here mainly to write CAN device driver under embedded Linux operating system. Linux device driver is the software interface between hardware and the Linux kernel, is to provide a set of standard user program interface for specific hardware, is not visible to the user. Linux the equipment is divided into three categories: character devices, block device and a network interface device, here use character device. Character device is not using the cache to access equipment, be like file access device, character device driver usually achieved open, close, read and write system calls. So the driver is to write the function, use the structure of file operations initialization, compile successful driver to generate Mcp2515.ko files, can be called by an application when Linux starts after loading. static struct file_operations dev_fops = {.owner=this_module,.ioctl=mcp2515_ioctl,.open =mcp2515_open,.read =mcp2515_read,.write =mcp2515_write, }; The code.owner statement module owner; mcp2515_write and mcp2515_read are responsible for processing and transmitting and receiving method of CAN bus data; mcp2515_open is responsible for opening the CAN bus controller, and empty the 3 send buffer and 2 receive buffers; mcp2515_ioctl entrance point for CAN devices under various operation command, the main completed set working mode, data frame, a device filter, ID bus baud rate etc.. Graphical interface Through the graphical interface, and users to exchange information is the most effective and convenient way, modern electronics, all control systems are basically using the graphical interface to control the operation of the form. A lot of graphical interface software, according to the different systems, different platforms, have different characteristics, the design is mainly to develop the embedded applications in the field of Qt software. QT development process is shown in figure 4. Conclusion Fig.4 QT development process CAN bus is stable, reliable data transmission, real-time high has gradually become the mainstream of industrial control network, this paper extends the CAN bus controller in the S3C2440 processor through the SPI bus interface, realize the S3C2440 bus communication and CAN function. MCP2515 due to the use of high-speed SPI interface to send and receive data, improves the CAN messaging capabilities, advantages of using CAN field bus and embedded Linux is excellent, the embedded technology and field bus technology, will have extensive application prospect in various fields.

5 520 Manufacture Engineering, Quality and Production System III Acknowledgment The article came from Hebei Provincial Key Disciplines of detection technology and automatic equipment. The work was supported by the Project of the Science and Technology Bureau of Langfang city(no ) and (No ). Corresponding Author Name, Jinmei liu ,liujinmeiht@126.com, Mobile phone, References [1] Du Shangfeng, Cao Xiaozhong, Xu Jin etc. CAN bus control technology and its application [M]. Beijing: electronic industry press, [2] Shi Jiugen. The CAN field bus system design technology [M]. Beijing: national defence industry press, [3] Wang Liming, Xia Li, Shao Ying etc. The design and application of the CAN field bus system [M]. Beijing: electronic industry press, (4) : [4] Liu Miao. Embedded system interface design and the Linux driver development [M]. Beijing: Beijing university of aeronautics and astronautics press, 2006 [5] Song Baohua. Linux device driver development explanation [M]. Beijing: people's posts and telecommunications publishing house, [6] Microchip.MCP2515/1-ASDataSheet,2005. [7] Microship company Stand-Alone CAN Controller with SPI Interface,2003. [8] Jasmin Blanchette, Mark Summerfield., etc. The C + + programming GUIQt4 [M]. 2. Yan Feng, Ceng Quan, Mr Zhang, eds. Beijing: electronic industry press, 2008

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