What do the L and H in automotive CAN bus represent?
2 Answers
In automotive CAN bus systems, the H stands for High data line while the L represents Low data line. Here are detailed specifications about CAN bus: 1. Concept: Developed by German company BOSCH in the early 1980s to address data exchange among numerous control and testing instruments in modern vehicles, CAN bus is a serial data communication protocol functioning as a multi-master bus. Communication media can include twisted pair cables, coaxial cables, or optical fibers, with transmission rates reaching up to 1Mbps. 2. Applications: A vehicle model may incorporate multiple control networks such as body, comfort, and multimedia systems. The body control typically uses CAN network, comfort systems employ LIN network, while multimedia utilizes MOST network. The CAN network serves as the primary backbone, managing critical modules like engine, transmission, ABS for vehicle safety, while sharing parameters such as RPM, speed, and oil temperature across all systems to enable intelligent vehicle functions. Examples include automatic door locking at high speeds and door unlocking upon airbag deployment.
When I first got into automotive electronics, I was also curious about what CAN bus L and H actually stand for. In vehicle networks, the CAN bus always uses twisted-pair wires for data transmission - L stands for CAN_Low (low-level line) and H stands for CAN_High (high-level line). These two wires always work in pairs and operate cooperatively. They use differential voltage transmission - for example, when the voltage on the H line increases, the L line synchronously decreases its voltage, with the voltage difference between the two signal lines carrying information. This design is particularly resistant to interference, working reliably even in electromagnetically complex environments like engine compartments. All the coordinated communication between vehicle controllers - like the engine and transmission coordinating gear shifts or the dashboard displaying various data - depends on this twisted pair. If one wire breaks or shorts, the vehicle may display network error codes, and in severe cases, might not even start.
