2.4G RF CAN bus automotive fault diagnostic

Controller Area Network CAN (Controller Area Network) within the complex for automotive electronics, controllers, measurement instruments to provide a uniform data exchange channels, have been widely used. Currently, too many car parts are provided a number of CAN bus communication interface.

In today's high-end cars are using CAN bus technology. For vehicle CAN bus fault occurs. Combine the advantages of RF and USB, KWP2000 application layer requirements depend on fault code, this paper, a vehicle based on CAN bus fault diagnostic design. The program is low cost, easy to carry, with strong flexibility and adaptability.

1 Design

System design block diagram shown in Figure l. System is divided into transmitter and receiver in two parts.

2.4G RF CAN bus automotive fault diagnostic

As a result of radio frequency technology to automotive CAN bus and CAN bus data acquisition part of the diagnostic part of the data can be separated without connection, without room space is limited, install and easy to carry. In accordance with the relevant ISO standard, CAN-bus transfer rates of up to 1 Mbps; However, the special environment within vehicles, vehicle CAN bus speed is generally 250 kbps. RF rate this system up to l Mbps, can satisfy the data transmission requirements.

Transmitter and receiver module with USB PC Interface for. USB and RS232 interface, or PCI, compared with user easy to use, equipment automatically identify and install drivers and configure, support dynamic access and dynamic configuration, etc; its transfer rate up to several Mbps, and supports both synchronous and asynchronous transfer way to guarantee bandwidth, transmission distortion.

PC side application layer software integrated application layer protocol KWP2000. KWP2000 developed by a Swedish car fault diagnosis agreement in computer-controlled automatic transmission, anti-lock braking system, airbags, cruise control has been widely used. It is based on OSI seven layer protocol in line with IS07498 standards. The first 1 to 6 layers of communication services to achieve the function of layer 7 to achieve the functions of diagnostic services. The application layer a set of comprehensive and standardized diagnostic code, the system uses the application layer protocol KWP2000 on CAN bus data collected from the analysis, in order to achieve the functions of fault diagnosis.
2 Hardware Implementation

About 2.1 system chip

2.1.1 nRF2401 chip

nRF240l a Single Chip RF Transceiver operates in 2.4 ~ 2.5GHz ISM band; built-in frequency synthesizer, power amplifier, crystal oscillator, modulator, and standard features such as SPI module; output power and communication channels available through software configuration, a total of 125 channels can be used, and the maximum rate of up to l Mbps. Chips with 1.9 ~ 3.6 V Wide operating voltage, the working energy is very low. When the power to launch a 5 dBm, the operating current of only 10.5 mA; receiver, the operating current of only 18 mA.

nRF240l There are 4 operating modes: send and receive mode, configuration mode, idle mode, shutdown mode. Its operating mode from the PWR_UP, CE, CS 3 pins and configuration bytes to determine the lowest TX_EN.

Transceiver mode is divided into DirectMode and ShockBurst. The former piece of the signal without any processing, the same with the other RF transceiver. Which uses on-chip FIFO stack, data from the MCU into low speed, but the high-speed launch, and associated with the RF protocol are all high-speed signal processing chip within. For example, nRF240l ShockBurst transceiver mode in the automatic processing of words first and the CRC checksum, the receiver automatically to remove the header and CRC check code; to send data automatically with prefix and the CRC checksum.

2.1.2 TMU3100 chip

TMU3100 Taiwan Tenx introduced RISC 2005 microcontroller core. It is embedded in a fully compatible USBl. An agreement, USB controllers, and provides a low-speed USB interface and 3 endpoints, including a control input / output endpoints and two interrupt input endpoint.

TMU3100 can be configured as a standard HID class, you can use the Windows operating system comes with the HID class driver. This eliminates the need for device driver development work, shorten the development cycle. TMU3100 chip structure shown in Figure 2 Box indiscriminately.

2.4G RF CAN bus automotive fault diagnostic

2.1.3 PICl8F2682 chip

PICl8F2682 is Microchip's new low-power 8-bit CAN microcontroller, the main resources are: built-in standard CAN module, 80KB Flash program memory, 1 KB of data E2PROM, 3.3 KBRAM memory, 8-Channel ADC, 1 個(gè)8-bit and three 16-bit T1MER, 1 個(gè) SPI and I2C serial communication ports, and programmable under-voltage reset and low voltage detection circuit.
PIC18F2682 built-in enhanced CAN bus module, the module contains the CAN protocol engine, information, and information control buffer. CAN CAN bus protocol engine automatically handles all incoming and outgoing messages, it can receive or send information to parse the data frame. Only need to register first to set the appropriate information can be sent by the relevant register of information transmission can be obtained by the state.

2.2 Hardware Circuit

2.2.1 Transmitter Circuit

Figure 3 is the system of the transmitter circuit. CAN bus interface using the company's built-in CAN module Microchip PIC18F2682 microcontroller, conducted by the optocoupler 6N137 bus isolation; CAN bus transceiver MCP2551.

2.4G RF CAN bus automotive fault diagnostic

PIC18F2682 chip with RF through a standard SPI interface, between nRF2401 SCK, SDI, SDO to complete, which can greatly enhance the sending rate. Configuration control of the nRF2401 enable CS and receiving, respectively sending to enable CE to control RB4 and RB5. When nRF240l received packets, DRl will be set high, so PICl8F2682 INT0 through inquiry to determine whether the state can receive the data.

2.2.2 Receiver Circuit

Figure 4 is a system receiver circuit. As TMU3100 by the PC power supply, while the PC USB interface, the voltage VDD provided by the interferences, it conducted a π filter on the VDD.

2.4G RF CAN bus automotive fault diagnostic

As TMU3100 no SPI module, it can be PB [1], PB [0] in accordance with the SPI protocol and nRF2401 the SPI port to communicate. Configuration control of the nRF2401 enable CS and receive, to send the enable CE by KSO [3] and KSO [13] control. After receiving the data packet nRF2401, DRl will be set high, so you can check KSl6 TMU3100 state has received enough data to judge.

3 Software Design
System software design, including software design transmitter, receiver and the PC-side software design software design.

3.1 Transmitter Design Software

Transmitter process shown in Figure 5. Software design to achieve two main functions: first, to achieve data acquisition CAN bus; second after the realization of the collected data through radio launch.

2.4G RF CAN bus automotive fault diagnostic

Power, the first of the CAN module initialization. Then initialize nRF2101, and to establish a connection with the receiver. When sending complete CAN data not received ACK signal, the frequency hopping; and inform the sender to resend the CAN is ready to receive data until the received ACK signal.

In order to prevent air interference, using an automatic frequency-hopping air agreement that whether or not to receive ACK signals are frequency hopping, it can prevent a band of strong interference, and thus reduce the error rate.

3.2 receiver software design

Receiver software process shown in Figure 6. Software design to achieve two main functions: first, to achieve enumeration; second is to achieve the received data upload via USB to the PC. Power, the first complete TMU3100 configuration, and with PC-enumeration; enumeration after the success of the nRF2401 configuration, and establish a connection with the transmitter. When receiving packets, the first thing to check is the CAN data or retransmission data command. If the CAN packet is returned to the ACK signal transmitter and frequency hopping, then the received data transmitted through the USB PC; If the retransmissions command, then the first frequency hopping, and retransmission flag set, indicating the next data packet is retransmitted packets.

TMU3100 is configured as a standard HID class, so do not develop drivers for the device, but the use of Windows to provide a standard HID class driver.

3.3 PC-side software design

PC-side software applications and device drivers by the components. Windows as a standard USB not prepared to provide a complete built-in drive, the system uses the Windows native HID class driver, as long as the TMU3100 configured for HID class, to complete the communication with the PC machine. This eliminates the need for developing device drivers, greatly simplifying the host computer software.

PC applications to achieve the primary function is to achieve TMU3100 endpoint reading and writing, with VC language, USB devices can operate as a file. With CreateFiile () function to obtain USB handle for read access or write access to open the specified endpoint. With DeviceControl () to carry out control operations, using ReadFile () to read data from the specified endpoint, with WriteFile () to write data to the endpoint.

When the CAN bus data is collected on the PC, you can diagnose the fault. KWP2000 diagnosis code is in accordance with the provisions of the application layer fault code design, is presently in general, and now the CAN application layer used in the future can be replaced by the new CAN upper layer protocol. Diagnostic Trouble Codes are defined in SSF14230 in. SAE J1979 in the system by the vehicle manufacturer or service provider-defined identifier value of different areas, such as listed in Table 1.

2.4G RF CAN bus automotive fault diagnostic

This table to hexadecimal number that the service identifier, with the data link layer service data bytes identify bytes within the corresponding SID. Different SID values represent different service requests, fault diagnosis procedures must conform to the application layer standards, to identify different hexadecimal code representing the different fault information.

4 Conclusion

This design of 2.4G wireless vehicle CAN Bus failure diagnostic apparatus, the use of automatic frequency-hopping air agreement, the error rate is almost close to zero, within the 14 m still work reliably. System uses the internationally accepted diagnostic code, so that program has the versatility and practicality; to PC as the hardware platform, without specialized hardware platform development, can significantly reduce development costs Bingjuyiyu achieve Shebei upgrade and maintenance; use the USB interface, and 2. 4G wireless communications, has a plug and play, not restricted by space, data transfer and real time features.