The problems of analysis of data on the CAN bus in vehicles

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1 Tomasz Jarosz 1 Comarch Technologies The problems of analysis of data on the CAN bus in vehicles Introduction Years of 80th and 90th is a breakthrough for automotive vehicles. Leading automotive companies have begun to implement in their vehicles innovative mechatronic solutions aimed at improving the performance, safety, comfort and environmental standards. To support the work of mechanical systems were introduced ever more complex electronic systems, which are responsible for the work of individual vehicle systems and components. An example of such a system could be the electronic stability program ESP called. Electronic Stability Program, i.e. An electronic circuit stabilizing the car when cornering, take control of interconnected systems ABS and ASR. There was, therefore, a need for efficient communication between the powerful modules, control various vehicle components, as well as the introduction of a central control unit and supervising the work of all The first vehicle onboard systems exchange data in an analog point-to-point configuration. Digital data from the microprocessor systems were converted to analog and sent large volumes of calls. This resulted in an excessive increase in the number of wires and electrical connectors. Analog signals are then converted back into digital form, understandable for the microprocessor system. Thus, the double convert the signal occurred (A/D and D/A), which after the data transmission has proved to be unnecessary and has been eliminated. The first transmission of digital data were used only for reading registered in the electronic modules faults (diagnostic scan). Scanners (testers) Diagnostic communicate with systems equipped with an internal memory of faults. Data transmission was off-board, i.e. On the outside, not used it for data exchange between vehicle electronic systems. In Figure 1 shows the topology of the diagnostic bus operation. External diagnostic tester via a common diagnostic lines K communicates with the drivers of individual electronic circuits. Fig. 1. K bus diagnostic topology. Source: [4] 1 T. Jarosz, Comarch Technologies, R&D Centre 1063

2 The necessity of rapid exchange of data on complex infrastructure contributed to the fact that automotive companies focused on the introduction of high-speed digital bus, spanning across dozens or even hundreds of controllers connected to each other via bus, under the supervision of specialized software on-board (Figure 2). Fig. 2. Data transmission system in the modern vehicle. Source: [4] This resulted in a decrease in the number of wires between modules and digital data exchange using more resistant to interference, reduced problem while transferring data via analogue. This eliminated the unnecessary AD and DA converters used only to transmit analog data. CAN bus The world leader in digital buses currently installed is the standard CAN - Controller Area Network, developed by Robert Bosch GmbH in 1986 [1]. CAN standard is to define the bus and data transmission protocol. The CAN bus is a bus broadcast, there is no separate master unit. Together with ISO and SAE standard J2284 CAN protocol has become the international standard for applications in passenger cars. Fig. 3. CAN bus topology. Source: [1] The CAN bus does not have a separate unit of the parent, because it belongs to a group bus multimaster. CAN messages can transmit any module connected to the bus and each system is equivalent in 1064

3 initiating transmission. At any given time only one station can act as a transmitter. Communication in CAN is a broadcast, ie. The messages broadcast on the bus are picked by all modules connected to it (the drivers). Also sending module receives your message. CAN message is accepted or ignored depending on whether the recipient is the addressee. Due to the broadcast nature of the transmission, and a large amount of data appearing on the bus, each module has a built-in filter hardware. Thanks to the module receives messages only of interest to him. CAN network identifies three layers of communication model: 1. Physical layer: Transmission medium, Signal voltage level, Speed transmission, 2. Transfer Layer: Message format, Detection and blocking errors Arbitration, Acknowledge receipt of the message, 3. Object Layer: Status messages Filtering messages. The physical layer defines the transmission medium for CAN bus, which consists of two wires made in the form of twisted completed impedances. Bus logic state is determined based on the voltage difference between the line CAN H and CAN L (Fig. 4). The physical data transfer is a method of encoding digital information NRZ (non-return-to-zero). This encoding is resistant to errors, distortions and reliable thanks to use of hardware and error checking. In order to detect transmission errors is sent polynomial correction also called CRC checksum. CAN uses the method SCMA / CA bus access with collision avoidance and detection of transmission errors. Method CSMA / CA requires a reaction time of all the drivers, not longer than the duration of one bit. Each device controller can transmit if the bus is free, at least for the duration of at least three bits of [5]. Fig. 4. Voltage and the logic state of the bus. Source: [1] 1065

4 Bit indicating a logical zero is predominant, number one is a bit recessive logical. The appearance of a logical zero is more important than the current there logic one is being used and to the priority bus access. If two modules at the same time they want to gain access to the bus, it gets precedence generating unit more dominant bits, i.e. logical zeros. Fig. 5. CAN bus node structure. Source: [1] Each controller (Fig. 3) connected to the CAN bus, also known as CAN bus node consists of a tranceiver CAN (transmitter / receiver), which performs the functions of the galvanic connection to the bus driver. This element is responsible for the conversion of dummy signals to form differential and protection against short circuits and power surges occurring on the transmission medium. CAN protocol controller is responsible for monitoring compliance with the rules of the CAN standard, error handling and access to the bus. The microcontroller controls and monitors the operation of an entire node (Fig. 5). Transfer the CAN network layer defines the format of messages, error detection and blocking, arbitration and acknowledgment of receipt messages ID 11 lub 29 bits Control bits 7 bits Data 0 8 bytes CRC 15 bits Fig. 6. CAN bus frame structure Source: [1] CAN frame begins with a start bit, which defines the beginning of the message and is a bit dominant [2]. Then there is the identifier. This field is 11 bits for standard CAN 2.0A or 29 bits for CAN2.0B. On the basis of the ID nodes carry out filtration frames. Acceptance filtering messages is done in hardware, so that the CPU load is reduced. ID also informs about the priority of the message - the lower the number, the higher the priority. If there is a collision with access to the bus, then you win message of higher priority. After detecting a collision, transmitting a message of a higher priority is continued and the transmitter currently a lower priority transmission interrupts and automatically repeats her soon after the release of the bus. The third field is a control field, determines how many bytes of data is in the frame and determines whether it is a remote frame. Remote frame is a special frame in which it is the usual identifier and does not contain data. Using this frame one controller requests data from another controller [3]. The last field is the CRC Cyclic Redundancy Check (15-bit checksum field). The checksum is calculated based on all preceding bits checksum field. Field Checksum bit ends located always in a state recessive. The duration of transmission of one message with eight bytes of data at a rate of 500 kbit / s is 225 microseconds (ID 11 bit) or 260 ms (29 bit identifier). Object layer describes methods for filtering of CAN messages sent, also determines whether it is a normal message or a request for download information. 1066

5 The CAN bus is fast and can be used everywhere where reliable communication is required. Adding new CAN module does not require any reconfiguration of the network. CAN bus analyzer CAN analyzer was developed as a powerful tool for identification, diagnosis and analysis of CAN bus in automotive engineering. With its help you can detect CAN bus wiring defects such as incorrect wiring, short to ground or supply plus and problems with impedance. Fig. 7. CAN bus analyzer structure. Source: The Author s material. CAN analyzer has been designed based on a powerful 32bit ARM processor. To handle the CAN bus uses two systems with the possibility of matching the impedance to that of the CAN bus. The use of USB transmission module significantly increased the transmission speed between the CAN analyzer and computer supervising his work, which in the case of the currently used CAN bus speed of 500 kb / s or more is important. Fig. 8. Standard mode topology. Source: The Author s material. CAN Tester working in standard mode is the ability to identify and track the bus all the frames appear on the CAN bus. CAN Tester when connected to the CAN bus automatically scans detecting standard transmission speed and adapts to them. In modern vehicles, the amount of information transmitted on the CAN bus is huge, because the analyzer is used for filtering messages Acceptance. This functionality allows you to define ranges or a single CAN frame identifiers on which the analyzer to operate on. This improves the ergonomics filtering definitely a lot of unnecessary information. With this scanner, we can extract the CAN frames generated by the device, and knowing this data, we can diagnose the correct operation even in the event of a fault emulate them. 1067

6 Fig. 9. Off-line mode topology Source: The Author s material. CAN analyzer can also be used as a generator of CAN frames; Such functionality will be very helpful in the diagnosis of CAN modules. When in scan mode enucleate correct question is generating mode using frames we can carry out the procedure for the diagnosis module. This procedure can be carried inside a vehicle or on a table diagnostic, and will consist in sending queries CAN and observing the response of the tested CAN module. Fig. 10. Bridge mode topology Source: The Author s material. The analyzer is equipped with two CAN interfaces and we can run it under the bridge. In this mode, we can connect two different buses together or separated by one of the two segments. This will allow us to control the CAN messages transmitted between bus segments and using an array of maps, including modification passed the frame. The frame captured in the first segment is modified by mapping and passed to the second segment. Built-in is a functionality which allows backwater correctness of transmission indicates a problem with communication in the event of intersection of the cable fault, poor impedance matching or during transmission errors suggesting a problem with the CAN module. CAN bus analysis As an example of practical application analyzer below shows the research done in the car Audi A4. During stops and drive analyzer followed CAN messages transmitted on the CAN bus. They observed changing values depending on the state of ignition, the operating state of the engine and vehicle speed. The following table shows registered CAN frames in hexadecimal format. Tab. 1. Examples of data recorded in the vehicle ID Długość Dane 3c E F de AD 1A 2B A9 12 3BE 8 6F 20 E FD 8 A8 DC 1F B E F

7 Frame with ID 0x3c0 the second byte and indicates the status of the ignition. After the tests made with the ignition key could be observed the following states: 0x01 - unlocked ignition key in position 1, 0x03 - unlocked ignition key in position 2, 0x07 - unlocked ignition key in position 4 starter turns. Frame 0x107 is connected to the motor, its value changed as a function of the current gear and the accelerator pedal position. During the driving has been observed 0x641 and 3BE frames with values varying depending on the direction and speed of the vehicle. These frames probably contained information of engine speeds and combustion. Frame 0x31B and 0x0FD having so low id, which is a high priority is probably derived from the ESP module, dynamically changing content during braking. In the frame of ID 0x5F0 we observed change in value of transferred data depending on the attached lighting. More accurate measurements and analysis, which was based on the above interception of CAN frames and then generating test data has shown that it is informing about the highlighted frame. The above analysis shows only part of the recorded results, the number of registered messages were much longer. Conclusion Technological progress has forced the need for effective communication offered by manufacturers systems are becoming more advanced, there is a need for an efficient data bus diagnosis. Specialized devices do not always meet all requirements imposed on them while their functionality is directly linked to the price proportionally. Presented analyzer enables efficient and effective CAN bus analysis, monitoring of transmitted messages and detect anomalies. CAN analyzer can be flexibly adapted to current needs, allowing you to exercise full control over the CAN network and its functionality does not differ from the more expensive commercial products. Streszczenie Artykuł zawiera opis magistrali danych CAN stosowanej w pojazdach, podstawowe informacje o protokole, a także opis zrealizowanego analizatora CAN i przykład jego zastosowania. Badania i analizy zostały wykonane w warunkach drogowych i laboratoryjnych w pojeździe Audi A4 z silnikiem diesel. Słowa kluczowe: magistrala CAN, analizator CAN, pokładowe systemy diagnostyczne, systemy transmisji danych w pojazdach. Abstract The article contains a description of the CAN data bus used in vehicles, basic information about the protocol, as well as a description of the realized analyzer CAN and an example of its use. Research and analysis were performed in the laboratory road conditions and the vehicle Audi A4 with diesel engine. Key words: CAN bus, CAN analyzer, on-board diagnostic systems, vehicle data transmission systems. LITERATURA / BIBLIOGRAPHY [1]. BOSCH CAN Specification Version

8 [2]. SCHMIDGALL, ZIMMERMANN: Magistrale Danych w Pojazdach. Protokoły i Standardy. Wydawnictwa Komunikacji i Łączności, WKŁ, Warszawa [3]. FRYŚKOWSKI, GRZEJSZCZYK: Systemy transmisji danych. Mechatronika samochodowa. Wydawnictwa Komunikacji i Łączności, WKŁ, Warszawa [4]. MERKISZ, MAZUREK: Pokładowe systemy diagnostyczne pojazdów samochodowych. Wydawnictwa Komunikacji i Łączności, WKŁ, Warszawa [5]. SCHAUFFELE, ZURAWKA: Automotive Software Engineering. Vieweg Verlag

Communication in Automotive Networks Illustrated with an Example of Vehicle Stability Program: Part I - Control Area Network

DOI 10.7603/s40707-013-0013-8 Communication in Automotive Networks Illustrated with an Example of Vehicle Stability Program: Part I - Control Area Network Grzejszczyk Elżbieta, Ph.D.eng. Docent, Electrical