What are the most important test items for CAN conformance testing?

The CAN conformance test is to reduce the difference of nodes in the CAN network, ensure the stability of the CAN network environment, and effectively improve the anti-interference ability of the CAN network. Therefore, the consistency test of CAN nodes is particularly important.

The CAN conformance test is to reduce the difference of nodes in the CAN network, ensure the stability of the CAN network environment, and effectively improve the anti-interference ability of the CAN network. Therefore, the consistency test of CAN nodes is particularly important.

What are the most important test items for CAN conformance testing?

With the development of concepts such as new energy and intelligent network connection, the body CAN bus environment has become complicated and disordered, and the unstable quality of CAN nodes poses a great threat to the safety of OEMs. Therefore, CAN conformance testing has become an important means to ensure the safe operation of CAN networks. The content of CAN conformance testing covers the physical layer, link layer, application layer and other test requirements, as shown in Table 1 CAN conformance test content (excerpt) ; Including input threshold, output voltage, sampling point, bit width tolerance key test items.

Table 1 CAN conformance test content (excerpt)

What are the most important test items for CAN conformance testing?

1. Input threshold test

Threshold testing is divided into invisible input voltage threshold and explicit input voltage threshold. When the node Vdiff is greater than 0.9V, it must be recognized as dominant, when it is less than 0.5V, it must be recognized as recessive. Between 0.5V and 0.9V, it belongs to an uncertain area. When Vdiff≤0.5V, the node can send messages normally, otherwise it means the node The work is in an abnormal state; when Vdiff>0.9V, the node must stop sending. If it does not stop, it means that the node is still recognized as a recessive level, and there is a misjudgment of level judgment; therefore, it is particularly important to test the input threshold of the device.

The purpose of the test is to check whether the explicit/recessive input voltage thresholds of CAN_H and CAN_L of the DUT comply with the definition of ISO 11898-2. The specific input voltage threshold standard is shown in Table 2 ISO 11898-2 input voltage threshold standard.

Table 2 ISO 11898-2 input voltage threshold standard

What are the most important test items for CAN conformance testing?

1. Test Principle

Under the bus load and common mode voltage conditions shown in Table 2 ISO 11898-2 input voltage threshold standard, the implicit/dominant input voltage is carried out according to the test principle of Fig. 1 Implicit input voltage test principle and Fig. 2 Explicit input voltage test principle Threshold test.

What are the most important test items for CAN conformance testing?

Figure 1 Principle of Implicit Input Voltage Test

What are the most important test items for CAN conformance testing?

Figure 2 Principle of visible input voltage test

2. Judgment basis

DUT can send messages normally when Vdiff≤0.5V (users can customize this range). At least in the case of Vdiff>0.9V (user-input), the DUT should stop sending frames.

2. Output voltage test

The signal amplitude on the CAN bus is the guarantee that the receiving node can correctly identify the logic signal; in the recessive state, if the CAN_diff voltage is greater than 0.9V, the bus will be in a continuous dominant state, causing the bus to be paralyzed; in the dominant state, if the CAN_diff voltage is greater than 0.9V The CAN_diff voltage is lower than 1.5V, indicating that the node’s driving ability is weak, which will lead to an error in the dominant level judgment, and it is prone to level flipping in a strong interference environment, leading to bus failure; as shown in Figure 3, the output voltage amplitude causes errors. .

What are the most important test items for CAN conformance testing?

Figure 3 The output voltage amplitude causes an error

Therefore, each manufacturer must test the output voltage amplitude of the CAN node DUT (device under test) before the product is put into use. The purpose of the test is to check whether the recessive/dominant output voltages of CAN_H and CAN_L of the DUT comply with the definition of ISO11898-2. As shown in Table 3, the ISO11898-2 output voltage standard is the test standard ISO 11898-2 output voltage standard.

Table 3 ISO11898-2 output voltage standard

What are the most important test items for CAN conformance testing?

1. Test Principle

Under the bus load conditions shown in Table 3 ISO11898-2 output voltage standard, the output voltage test is performed according to the test principle of the output voltage test principle in Figure 4.

What are the most important test items for CAN conformance testing?

Figure 4 Principle of output voltage test

2. Judgment basis

If the test result meets the ISO 11898-2 output voltage standard in Table 3 ISO11898-2 output voltage standard, the test is passed.

Three, sampling point test

The sampling point is the location where the receiving node judges the signal logic. CAN communication is asynchronous communication, and continuous resynchronization is required to ensure accurate sampling of the receiving and sending nodes; if the sampling point is too far forward, sampling errors are prone to occur due to the cable; If the sampling point is too far behind, due to SJW, the synchronization jump width of the receiving node will be adjusted (adjust its own clock to match). If the adjustment is not good, errors will easily occur; therefore, it is particularly important to test the sampling point of the CAN node.

The purpose of the sampling point test is to check whether the sampling point of the CAN message signal sent by the DUT complies with the specification requirements;

What are the most important test items for CAN conformance testing?

1. Test Principle

Start CANstress receiving message interference function, as shown in Figure 5 CANstress receiving message interference function. From the 45% position of the bit time, the interference increases by 1% each time until 100%; the error message of CANScope-Pro is recorded through statistics, and the interference point of the error message is equal to the sampling point.

What are the most important test items for CAN conformance testing?

Figure 5 CANstress receive message interference function

2. Judgment basis

The sampling point of the CAN message signal sent by the DUT should be within the range defined by the specification: 75%≤SP≤83.4%.

Four, bit width tolerance test

Tolerance represents the baud rate range (bit time range). Increasing the tolerance can help to receive messages from other nodes; sampling points and tolerance are important factors for evaluating the adaptability of CAN nodes. SJW (Synchronous Jump Width) determines whether the receiving node can have better compatibility. If the receiving node SJW does not adjust the baud rate properly, it will lead to insufficient bit width tolerance and errors; therefore, bit width tolerance test It is also one of the important test items to ensure the stability of the signal.

The bit width tolerance test is used to check whether the bit width tolerance of the CAN message sent by the DUT complies with the definition of ISO 11898-2.

1. Test Principle

Use the bit width tolerance test function, as shown in Figure 6 Bit width tolerance test. Take the DUT baud rate as the standard, configure the baud rate deviation to gradually increase by 1%, and send a message to the CAN network; judge whether the network has message error information feedback, if there is error feedback, end the test, and judge whether the result is in the standard Within the interval.

What are the most important test items for CAN conformance testing?

Figure 6 bit width tolerance test

2. Judgment basis

The bit width tolerance range should meet at least -4≤SJW≤4% (the range can be set by the user).

Five, CANDT conformance test system

The CANDT conformance test system released by ZLG Ligong Technology-Zhiyuan Electronics can automatically complete CAN node physical layer, link layer and application layer conformance tests. It is the only one in the current CAN bus test field that can perform complete physical layer automated tests and export reports. equipment. It avoids the error of manual measurement and statistics, and at the same time cooperates with the method of automated testing to reduce the waste of test time, improve the accuracy of the test, and greatly save labor costs.

What are the most important test items for CAN conformance testing?

Users can check the required test items on the software page to perform fully automated tests. If you only want to test the output voltage, check the voltage test items separately. After the test is completed, the user can export the automated test report, as shown in the test report in Table 4. According to the test report, the standard source of test items, test procedures, and judgment basis can also be tracked. The OEM can evaluate the quality of CAN nodes based on this report as a basis for the entry of the OEM and ensure the stability of the CAN network environment of the vehicle.

Table 4 Test report

What are the most important test items for CAN conformance testing?

The CANDT conformance test system is based on CANScope’s underlying analysis capabilities, integrates oscilloscopes, power supplies and other necessary equipment, can cover the CAN conformance test standards of OEMs, and establish a CAN bus test and guarantee system for OEMs and component companies.

The Links:   CM600HA-12H 2DI200M-050

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