As the electronic control system unit (ecu) is widely used in automobiles, the degree of electronicization of automobiles is getting higher and higher. Although the increase of the electronic control system has improved the power, economy and comfort of the car, the accompanying complicated circuit will inevitably lead to the huge and complicated body wiring and the shortage of installation space. At the same time, in order to improve the information utilization rate of the electronic control unit, a large amount of data information is required to be shared among different electronic units, and a large number of control signals in the automobile integrated control system also need to be exchanged in real time, and the data communication between different functional electronic control system units becomes Must be more and more important. Therefore, higher and higher requirements are placed on the design of electronic control system units. Not only the communication network should have the characteristics of high communication rate, accuracy and high reliability, but also the control module should have high control effectiveness and small space. advantage.
In this paper, based on the CAN bus technology, the electronic control system unit used in the automotive network system is designed and developed.
1 Electronic control system unit can communication module design
According to the principle of can communication, the hardware of can communication module of electronic control system unit is mainly composed of can controller, can driver and central microprocessor. The traditional can communication module uses 51 series single-chip microcomputer as the central processor, sja1000 as the can controller, and pca82c250 as the can driver. This kind of solution occupies a large space, the peripheral interface expansion is limited, and the power consumption is high. In this design, we use the lpc2119 and tja1050 bus driver with embedded can controller to form the can communication module of the electronic control system unit. The hardware diagram of the can communication module is shown in Figure 1.
The lpc2119 has an arm7 core, which has the advantages of small package, low power consumption, multiple 32-bit timers, 4 10-bit adcs, 2 cans, and up to 9 external interrupts. tja1050 is produced by philips company to replace the high-speed CAN bus driver of pca82c250. The device provides the interface between the can controller and the physical bus and the differential sending and receiving functions of the can bus. For the end nodes composed of "weak" terminals, the resistance and capacitance around the tja1050 can improve the system's emc performance. Practice has proved that using lpc2119 and tja1050 to construct a can communication module has strong peripheral expansion capability and small space, and at the same time improves electromagnetic radiation (eme) performance and anti-electromagnetic interference (emi) performance.
2 Design of electronic control system unit control module
The traditional "spider-web" control module has complicated circuits and high maintenance difficulty. In this design, we use a combination of power module, man-machine communication module, and state quantity input module to construct an electronic control system unit control module, which improves the observability and effectiveness of the entire system. The hardware diagram of the control module is shown in Figure 2.
2.1 Power module
Considering the large power load of the car and the limitation of the lpc2119 i / o port drive, the power module is used as a bridge between the central microprocessor and the power load in the system.
In the design, we use the mc33888 power device produced by Motorola to control the high beam light, low beam light, reversing light and brake light. mc33888 integrates four high-end lamp drivers and eight relay or LED drivers. It is a controllable network, which has the advantages of on-board diagnosis, error reporting capability with the microcontroller, and fault softening. Considering the relatively large power of interior lights and gallery lights, we use mc33487 power devices for control. The mc33487 internally integrates two 20-ohm high-end drivers with current sensing, with a current output of 4.5a. Inductive loads and high-current short-circuit protection are the difficulties of the entire design. mc33887 has the advantages of low power consumption, short-circuit shutdown of 25 microamperes in standby mode, and output current exceeding 8 amperes. Therefore, the system uses mc33887 power devices to control the motor, lock, antenna, and washing pump.
2.2 Human-machine communication module
In order to improve the comfort and safety of drivers and passengers, the entire system must establish a good human-machine communication module between humans and machines. bc7281, the combination of the keyboard module and the peripheral led to construct a man-machine communication module. bc7281 is a 16-bit digital tube display and keyboard interface dedicated chip launched by Bigao. The chip can control 16 digital tubes or 128 independent LEDs through external shift registers (74hc164, 74ls595, etc.). The drive output polarity and output timing of bc7281 can be controlled by software, so as to cooperate with various drive circuits, suitable for any size of digital tube. Through the human-machine communication module, human consciousness can be recognized by the machine, and at the same time, the machine can also feed back some corresponding state information to the LED or LCD to achieve the visualization effect of the man-machine communication.
2.3 State quantity input module
The state quantity input module mainly feeds back some artificial operation effects (such as headlight switch and turn signal switch), body state (such as door and window switch) and internal state information (such as oil quantity and water temperature) to the central processor. By analyzing and processing the feedback information, the central processor can accurately judge the situation of the vehicle and make corresponding operations.
The external state information can be divided into switch quantity and analog quantity. Through a series of peripheral circuits (such as plastic anti-shake circuit), we convert the switch into 0v and + 5v high and low levels that can be recognized by the CPU. In the analog quantity processing, firstly through the normalization processing circuit, the changes of water temperature, oil volume, air pressure, and room temperature are converted into electrical signals between 0v and 5v, and then converted into 4-channel 10-bit ad converter embedded in lpc2119 The corresponding digital quantity. The existing CAN communication module is used to transmit these digital quantities to the electronic control system unit near the driver, and then through the d / a converter to be reflected on the instrumentation.
3 Electronic control system unit software design
For the lpc2119 microprocessor, the can controller is completely triggered based on events, that is, when its state changes, the can controller will tell the microprocessor the result of the state change. Therefore, the central microprocessor can use interrupts or polling to make corresponding processing to the can controller. The complete can firmware programming hierarchy diagram is shown in Figure 3.
Each electronic control system unit sends data to the bus according to the prescribed format and cycle, and at the same time takes the required messages according to the needs. For receiving data, the system uses interrupt method to achieve, once the interrupt occurs, the received data will be automatically loaded into the corresponding message register. At this time, the mask filter register is used to selectively compare the identifier of the received message with the identifier set in advance during the initialization of the receive buffer, and only the messages with the matching identifier can enter the receive buffer. The required message will be shielded from the receiving buffer, thus reducing the burden of the CPU to process the message. The application program of each electronic control system unit is different, but the application program of the communication module is basically the same, which can be divided into can initialization, sending data, and receiving data.
3.1 can initialization procedure
The can initialization program is mainly used to realize the parameter setting when the can works. The main contents of the initialization include: hardware enabling can, setting can alarm limit, setting bus baud rate, setting interrupt working mode, setting can acceptance filter working mode, Set the working mode of the can controller, etc. The initialization flow chart is shown in Figure 4.
3. 2 Send data program
After the can module is initialized successfully, it can be used to transmit messages. The process for a node to send a message to the bus is:
lpc2119 composes a frame message according to the can format to the data to be sent, writes into the can module to send the buffer, and then starts the sending command, and sends the message to the bus. The sending flowchart is shown in Figure 5.
One thing must be noted when using the send function, because after starting the command to send data, the can controller will return the status of whether the frame data has been sent successfully after sending the data in the buffer. In this way, if the function has been waiting for the data to be sent, the performance of the entire microprocessor will be reduced. In order to avoid this situation, the function returns immediately after starting the transmission, and judges whether the transmission is successful by sending an interrupt or querying the tcs status bit.
3.3 Data receiving program
In this design, we use the interrupt method to receive data on the CAN bus. When an internal interrupt occurs in the can controller of lpc2119, we first identify the ri bit of the interrupt register, determine whether it is a receive interrupt, and then read the content of the receive buffer. The receiving flow chart is shown in Figure 6.
4 Conclusion
Practice has proved that based on the CAN bus technology, the automotive electronic control system with arm7 core has a small unit space and high effectiveness. In particular, its data communication has strong real-time, higher reliability and better anti-interference ability, even under heavy load, there will be no network paralysis, but investment in practical use still needs further research and Improvement, and the communication processing ability, error correction and fault tolerance of the program need to be further improved.
In this paper, based on the CAN bus technology, the electronic control system unit used in the automotive network system is designed and developed.
1 Electronic control system unit can communication module design
According to the principle of can communication, the hardware of can communication module of electronic control system unit is mainly composed of can controller, can driver and central microprocessor. The traditional can communication module uses 51 series single-chip microcomputer as the central processor, sja1000 as the can controller, and pca82c250 as the can driver. This kind of solution occupies a large space, the peripheral interface expansion is limited, and the power consumption is high. In this design, we use the lpc2119 and tja1050 bus driver with embedded can controller to form the can communication module of the electronic control system unit. The hardware diagram of the can communication module is shown in Figure 1.
The lpc2119 has an arm7 core, which has the advantages of small package, low power consumption, multiple 32-bit timers, 4 10-bit adcs, 2 cans, and up to 9 external interrupts. tja1050 is produced by philips company to replace the high-speed CAN bus driver of pca82c250. The device provides the interface between the can controller and the physical bus and the differential sending and receiving functions of the can bus. For the end nodes composed of "weak" terminals, the resistance and capacitance around the tja1050 can improve the system's emc performance. Practice has proved that using lpc2119 and tja1050 to construct a can communication module has strong peripheral expansion capability and small space, and at the same time improves electromagnetic radiation (eme) performance and anti-electromagnetic interference (emi) performance.
2 Design of electronic control system unit control module
The traditional "spider-web" control module has complicated circuits and high maintenance difficulty. In this design, we use a combination of power module, man-machine communication module, and state quantity input module to construct an electronic control system unit control module, which improves the observability and effectiveness of the entire system. The hardware diagram of the control module is shown in Figure 2.
2.1 Power module
Considering the large power load of the car and the limitation of the lpc2119 i / o port drive, the power module is used as a bridge between the central microprocessor and the power load in the system.
In the design, we use the mc33888 power device produced by Motorola to control the high beam light, low beam light, reversing light and brake light. mc33888 integrates four high-end lamp drivers and eight relay or LED drivers. It is a controllable network, which has the advantages of on-board diagnosis, error reporting capability with the microcontroller, and fault softening. Considering the relatively large power of interior lights and gallery lights, we use mc33487 power devices for control. The mc33487 internally integrates two 20-ohm high-end drivers with current sensing, with a current output of 4.5a. Inductive loads and high-current short-circuit protection are the difficulties of the entire design. mc33887 has the advantages of low power consumption, short-circuit shutdown of 25 microamperes in standby mode, and output current exceeding 8 amperes. Therefore, the system uses mc33887 power devices to control the motor, lock, antenna, and washing pump.
2.2 Human-machine communication module
In order to improve the comfort and safety of drivers and passengers, the entire system must establish a good human-machine communication module between humans and machines. bc7281, the combination of the keyboard module and the peripheral led to construct a man-machine communication module. bc7281 is a 16-bit digital tube display and keyboard interface dedicated chip launched by Bigao. The chip can control 16 digital tubes or 128 independent LEDs through external shift registers (74hc164, 74ls595, etc.). The drive output polarity and output timing of bc7281 can be controlled by software, so as to cooperate with various drive circuits, suitable for any size of digital tube. Through the human-machine communication module, human consciousness can be recognized by the machine, and at the same time, the machine can also feed back some corresponding state information to the LED or LCD to achieve the visualization effect of the man-machine communication.
2.3 State quantity input module
The state quantity input module mainly feeds back some artificial operation effects (such as headlight switch and turn signal switch), body state (such as door and window switch) and internal state information (such as oil quantity and water temperature) to the central processor. By analyzing and processing the feedback information, the central processor can accurately judge the situation of the vehicle and make corresponding operations.
The external state information can be divided into switch quantity and analog quantity. Through a series of peripheral circuits (such as plastic anti-shake circuit), we convert the switch into 0v and + 5v high and low levels that can be recognized by the CPU. In the analog quantity processing, firstly through the normalization processing circuit, the changes of water temperature, oil volume, air pressure, and room temperature are converted into electrical signals between 0v and 5v, and then converted into 4-channel 10-bit ad converter embedded in lpc2119 The corresponding digital quantity. The existing CAN communication module is used to transmit these digital quantities to the electronic control system unit near the driver, and then through the d / a converter to be reflected on the instrumentation.
3 Electronic control system unit software design
For the lpc2119 microprocessor, the can controller is completely triggered based on events, that is, when its state changes, the can controller will tell the microprocessor the result of the state change. Therefore, the central microprocessor can use interrupts or polling to make corresponding processing to the can controller. The complete can firmware programming hierarchy diagram is shown in Figure 3.
Each electronic control system unit sends data to the bus according to the prescribed format and cycle, and at the same time takes the required messages according to the needs. For receiving data, the system uses interrupt method to achieve, once the interrupt occurs, the received data will be automatically loaded into the corresponding message register. At this time, the mask filter register is used to selectively compare the identifier of the received message with the identifier set in advance during the initialization of the receive buffer, and only the messages with the matching identifier can enter the receive buffer. The required message will be shielded from the receiving buffer, thus reducing the burden of the CPU to process the message. The application program of each electronic control system unit is different, but the application program of the communication module is basically the same, which can be divided into can initialization, sending data, and receiving data.
3.1 can initialization procedure
The can initialization program is mainly used to realize the parameter setting when the can works. The main contents of the initialization include: hardware enabling can, setting can alarm limit, setting bus baud rate, setting interrupt working mode, setting can acceptance filter working mode, Set the working mode of the can controller, etc. The initialization flow chart is shown in Figure 4.
3. 2 Send data program
After the can module is initialized successfully, it can be used to transmit messages. The process for a node to send a message to the bus is:
lpc2119 composes a frame message according to the can format to the data to be sent, writes into the can module to send the buffer, and then starts the sending command, and sends the message to the bus. The sending flowchart is shown in Figure 5.
One thing must be noted when using the send function, because after starting the command to send data, the can controller will return the status of whether the frame data has been sent successfully after sending the data in the buffer. In this way, if the function has been waiting for the data to be sent, the performance of the entire microprocessor will be reduced. In order to avoid this situation, the function returns immediately after starting the transmission, and judges whether the transmission is successful by sending an interrupt or querying the tcs status bit.
3.3 Data receiving program
In this design, we use the interrupt method to receive data on the CAN bus. When an internal interrupt occurs in the can controller of lpc2119, we first identify the ri bit of the interrupt register, determine whether it is a receive interrupt, and then read the content of the receive buffer. The receiving flow chart is shown in Figure 6.
4 Conclusion
Practice has proved that based on the CAN bus technology, the automotive electronic control system with arm7 core has a small unit space and high effectiveness. In particular, its data communication has strong real-time, higher reliability and better anti-interference ability, even under heavy load, there will be no network paralysis, but investment in practical use still needs further research and Improvement, and the communication processing ability, error correction and fault tolerance of the program need to be further improved.
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