Research And Development Of Automotive Collect Central Uint

Automotive electronic technology has developed rapidly in recent years. Some foreign limousine have use CAN bus maturely for communication between automotive functional components. Since the Mercedes - Benz use two CAN bus network to achieve the different features of the communication in bus in 1992. A large number of auto manufacturers begin to use this technology. This is also the goal of this system's design-CAN bus network. Because of the importance of vehicle information, the study of automotive collect central unit in CAN bus systems is essential.As the design of automotive CAN bus system is still in its infancy, this paper presents a simulation design automotive collect central unit based on CAN bus. The unit is used as a monitor on semaphores of a variety of sensors. It also can record and analyze the data. The unit can send the alarm message to the other units to monitor driving situation, and provide the real-time and effective data for the control of the vehicle, to improve driving safety.The system design includes hardware design and software design. Hardware design was based on LPC2129 processor. Its work includes the design of data acquisition circuit, data storage circuit, CAN Bus interface circuit, the clock chip circuit. The data acquisition circuit is the focus of this article, which includes collect three semaphores of the automobile, analog signal, digital signal, switching signal. The automotive analog signal is mainly from the signals which are the output from various sensors. Generally the signal is the resistance and voltage. This part is designed to realize how to use the LPC2129 processor's A / D converter to collect the voltage and resistance, through collecting the signal of the PT100 temperature sensor and variable resistor-type liquid level sensor. Switching signal collection is relatively simple. With an analog switch named CD4067 we can use a small amount port to collect the signal of multi-IO port switch. Pulse signal is mainly from the rolling speed of engine and the vehicle speed, the design realize the Hall-effect speed sensor signal acquisition based on the principle of Hall switch sensor A3144. The part of software design includes the study of LPC2129 processor and use LPC2129 processor's hardware resources to achieve the software function of each circuit module. Its main task is to read and write the register of AT45DB321, display the information on LCD, provide the clock information with the clock chip and realize CAN bus communication.AT45DB321 is a FLASH memory which is size of 32Mbits. Unlike the conventional FLASH memory, it has large capacity, fast speed to read, simply operation and simple serial interface for applications of digital voice storage and data storage. DS1302 is a low-power clock chip, which provides a function of trickle charge. Its unique structure of dual power supply ensures that it can still work with the battery supply in the case that the system is power down. LCD12864 make the great convenience for debugging. With character library in LCD12864, we can easily display the information on LCD12864.The design of CAN bus communication is also the focus of this article. CAN bus is a field bus technology which has international standard. It uses twisted-pair structure and differential signal transmission, which ensure that communications is reliability, security, strong anti-interference. It can connect up to 110 nodes, and its transmission speed can be up to 1Mbps. The speed of communication reduce as the transmit distance increases. CAN bus protocol is divided into CAN2.0A and CAN2.0B, the difference is not the same as the identifier, the former is 11 bits identifier, the latter is 29 bits identifier, LPC2129 CAN controller processor is compatible with both protocols. CAN bus protocol provide four different data transmission formats, data frame, remote frame, error frame, overloading frame. Data frame used to transmit data, the remote frame used to request data transmission, error frame used CAN node notify other node that there be have an error occurred when discovered errors, overloading frame used for CAN bus node informing other units that the unit is busy. CAN bus protocol provide powerful functions of error detection and acceptance filter. Error detection can determine error conditions on the bus, and through read the value of the sending error register and the receiving error register, CAN bus node determine the bus is in which status, active error state, passive error state and the state that the bus turned off, thereby enhancing the reliability of CAN bus transmission. Acceptance Filter uses the hardware to complete the filtering by matching the identifier to determine whether this message is ignored or accepted. In this design, not only completed the design of hardware the CAN transceiver interface and also write the code of CAN bus communication.The system has realized the basic function includes collecting the temperature, liquid level and the speed, communicating between CAN nodes, storing the data, analyzing the data and providing the real-time clock. When an error occurs, it also can send alarm signal to the other node. I believe that after a large numbers of experiments the design of the CAN bus system will apply to the actual vehicle and bring good economic and social benefits.