Why do OEMs pay more and more attention to CAN conformance testing?
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The CAN conformance test requires that the nodes in the CAN network of the vehicle meet the CAN bus node specification requirements, reduce the node differences in the CAN network, ensure the environmental stability of the CAN network, and effectively improve the anti-jamming capability of the CAN network. Why does the OEM increase the importance of CAN conformance testing?
First, vehicle CAN network architecture
In the past, there were few nodes in the CAN bus network of traditional vehicles, such as instruments and engine ECUs. However, with the development of the new energy automotive industry, the nodes in the vehicle CAN network have evolved to be extremely complex. Now the number of CAN nodes in the new energy vehicle has reached 60, which is subdivided into multiple CAN network systems. For example, the body part contains air conditioners, doors, navigation
Complete vehicle complex CAN network
Second, the inconsistency of CAN bus
The complicated CAN network, the quality of each node is not good, there will be a big security risk to the CAN bus network. Usually one of the nodes will affect the normal operation of the whole bus, and even lead to the failure of the overall bus.
1, the bus 瘫痪
For example, a CAN network includes nodes A, B, and C. The differential voltage at node A is 1.2V, while the differential voltage at node B is 2.0V, and the differential voltage at node C is 1.8V. When the vehicle's CAN network operates in a strong electromagnetic interference environment, the common mode interference of the environment will cause the differential voltage of the node A to affect below 0.9V in the CAN bus, causing the node to roll over from the dominant level to the recessive level. , Which led to the failure of node A work, frequent error frames. In the CAN bus, although the error frame is not received, it still occupies the bus transmission time, so it causes other normal nodes to send delays or unable to send, which affects the normal operating environment of the CAN bus of the vehicle.
Solution: The host plant must require that the operating voltages of nodes A, B, and C must operate at 1.8V or even 2.0V. This problem is solved.
At other nodes, the safety system also contains airbags, detonators and other nodes.
Error frame occupation bus
2. Inconsistent baud rate causes CAN network system to crash
Bit time (bit width) and baud rate are the most basic elements of CAN bus communication. Bit time = 1/baud rate, such as the baud rate is 500k, and the time is 2us. In the same CAN bus sampling frequency, when the bit time of a certain node is dithered, ie the bit time is 1.8us or 2.2us, it will cause abnormal logic judgment of the sampling point, bus error occurs, and the CAN network system will crash.
Solution: During the CAN network admission phase, if the nodes of the access network are normalized, the bit time of each node must satisfy t=2us±3%, then the bit time of the CAN network will be highly consistent and can be from the CAN bus. The physical layer circumvents this problem.
Baud rate jitter causes bit time changes
3, the determination of the dominant threshold level error causes the vehicle network failure
In general, the CAN bus determines the recessive mechanism as follows: when the differential level is greater than 0.9V, it is a dominant level; and when it is less than 0.5V, it is a recessive level, among which is between 05V and 0.9V. Uncertain area. However, in a real network, a node in a CAN bus network is still judged to be recessive when the differential level is 0.9V, and then a bit logic judgment error occurs, which in turn causes the node to send an error frame, causing the bus to fall into a network failure state.
Solution: As in the CAN network node admission phase, perform an explicit threshold test on each node and use a voltage source to raise the differential voltage to 0.9V to ensure that all nodes can be judged to be dominant at this differential voltage, and Stopping the transmission of messages will reduce the occurrence of this bus fault and relieve the workload of the CAN bus network debugging.

Therefore, in order to ensure the stability of the CAN bus, it is necessary to conduct CAN conformance testing on the vehicle network. As the overall designer of the CAN bus network, what are the contents of the CAN conformance test and how to ensure the stability of the CAN bus through the CAN conformance test?
Third, CAN consistency test content and solution
1, CAN compliance test content
In China, most of the OEMs have CAN bus network test specifications. The main contents include the physical layer, link layer, and application layer.
l Physical layer: The physical characteristics of the communication medium, such as amplitude and edge time, are the most important parts.
l Link layer: Specifies the arrangement and organization of the transmission on the medium, such as the frame structure;
l Application layer: Information exchange between users, software, and network terminals, with more customer-defined content;
The physical layer in the physical characteristics of the media, mainly from the standard ISO 11898, the part of the standard is highly consistent. In the link layer and the application layer, because the OEM's vehicle network design is different, its application layer testing is inconsistent.
CAN Conformance Test Content (Extract)
2nd, CAN conformity test plan
CAN conformance testing tools include CAN card, oscilloscope, power supply and other devices. Currently, domestic CAN bus engineers can only manually build test platforms and perform item-by-item tests, mainly collecting data from CAN cards, and testing waveforms through an oscilloscope. The purpose of testing the time, amplitude, and width of the test bit is achieved, but the test plan is less efficient, and generally it takes 10 hours or even 1 day for the overall CAN compliance test project to be completed.
Manually test the architecture
The upcoming CANDT conformance test system of ZLG Zhiyuan Electronics is based on CANScope low-level analysis capability, integrates necessary equipment such as oscilloscope and power supply, can cover the host plant's CAN conformance test standard, and fully automate the CAN bus conformance test, as a host plant and parts and components Enterprises to establish CAN bus testing and security system. In addition, the CANDT can also output test reports based on the test results, which serves as the basis for host plant access, greatly reducing the workload of the host plant in the network debugging process, and ensuring the stability of the entire vehicle CAN network environment.

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