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With the increasing number of automotive electronic devices, using serial buses for multi-channel transmission to form automotive electronic networks is a reliable and cost-effective approach. In the original traditional automotive circuits, the connections between the powertrain module and the body module were point-to-point connections; as a result, the wiring became increasingly complex, and the increase in wiring led to a higher rate of vehicle failures. Later, the CAN bus was used more and more widely in cars. Multiplexing refers to the method in computer local area networks of transmitting multiple types of information together or in sequence through a single communication channel. A network with multiplexing capabilities allows multiple computers to access it simultaneously. The use of CAN (Multi-Channel Transmission Technology) in automobiles allows for simplified wiring, reduced costs, easier and faster communication between electronic control units, a smaller number of sensors, and the sharing of information resources. Multiplexed communication networks are applied to multi-module operating systems. The modules are connected to each other using ordinary twisted pair cables, and data link connectors are used as diagnostic interfaces. Information exchange takes place in a manner similar to shared telephone lines, with modules communicating using information and dedicated enterprise standard protocols. The information content includes control, status or diagnostic information, as well as operating parameters, etc. Twisted pair has the advantage of providing redundancy, meaning that if one line is interrupted, the other line can ensure the system continues to operate. Moreover, twisted pair reduces external electronic interference to multi-channel communication networks, as well as the electronic interference generated by the networks themselves. Let’s take a look at how to use an oscilloscope to measure the CAN bus signals in a vehicle. First, locate the vehicle’s OBD interface and check the definitions of its pins: 4. Vehicle ground; 5. Signal ground; 6. CAN high (ISO 15765-4); 14. CAN low (ISO 15765-4); 16. Battery voltage; 3. CAN high (alternate); 11. CAN low (alternate). Connect channels 1 and 2 of the oscilloscope using BNC-to-banana plug cables, with the black banana plug connected to a alligator clip in order to connect to pin 4 for grounding. Channel 1 is connected to OBD PIN6 (CAN_H), and channel 2 is connected to OBD PIN14 (CAN_L). Open the oscilloscope’s decoding menu to configure the CAN bus. Adjust the bus threshold level to obtain the decoded data; set the triggering mode to decoding trigger, as well as a stable waveform for the data frame ID. Adjust the vertical scale and time base to observe the signal. As shown above, this is the normal waveform of CAN-BUS; the CAN-H and CAN-L waveforms are identical but have opposite polarities. When the CAN-BUS system is in sleep mode, the electronic control unit ECU introduces the battery voltage into the CAN-H and CAN-L lines through the EN and STB connectors. At this time, the CAN-H voltage is close to 12V, while the CAN-L voltage is close to 0V. If the CAN-H line is short-circuited to ground, then the CAN-L line will transmit a normal signal waveform, with the CAN-H signal voltage at 0V. When the CAN-L line is short-circuited to ground, the CAN-H line also transmits a normal signal waveform, with the CAN-L signal voltage at 0V. If both the CAN-H and CAN-L lines are short-circuited to ground, then the voltage of both signals is 0V. When the CAN-H and CAN-L lines are short-circuited to each other, their signal voltage polarities are the same, and their waveforms tend to be identical. When the CAN-H line pair is shorted to the power supply, its voltage remains at 12V, while the waveform of the CAN-L line is normal. When the CAN-L line pair is shorted to the power supply, its voltage remains at 12V, while the waveform of the CAN-H line is normal. When both CAN-L and CAN-H are short-circuited to the power supply, their voltages are both the battery voltage. When the CAN-H line is open, its waveform remains normal, while the CAN-L line stays at 0 voltage at all times. When the CAN-L line is open-circuited, the voltage on the CAN-L line remains at a high level of 5V, while the waveform of the CAN-H line stays normal. Types of CAN frames: Data Frame: Used to transmit data ranging from 0 to 8 bytes. Remote Frame: A remote frame is used to request other nodes to send data frames with the same ID. Error Frame: An error frame is sent by any node on the bus whenever an error is detected. Overload Frame: An overload frame is generated when the bus load is too high, between data frames or remote frames. Some oscilloscopes come with built-in setup software, allowing relevant parameters to be automatically set by simply clicking.