CAN bus Tutorial

Why does the CAN bus exist?

To solve a technical and economic problem caused by wiring. At first, the electrical and electronic system of a vehicle was made up of only two main control units: the engine ECU and the body computer for managing the cabin’s electrical functions. These units were directly connected to sensors and actuators, as if each system were isolated. As vehicle features grew, more control units, sensors, and actuators were added—and so did the number of cables. At a certain point, the amount of wiring created serious issues: rising costs, more complex assembly, and difficult troubleshooting in case of failures. A smarter system was needed, one that could use the same cables as data highways, allowing several control units to share them. This is how CAN was born—to make vehicles more functional in a sustainable way.

What are the main features of the CAN bus ?

It is a relatively simple system, low-cost, robust, yet flexible. Its huge popularity has encouraged competition, which in turn lowered the cost of devices and materials connected to this technology. The cable consists of two twisted wires, and each control unit has a transmitter and receiver capable of encoding and decoding information on the CAN bus. Some versions of CAN bus can even continue working if one of the two wires is cut or short-circuited. Control units can be added or removed from the network without disrupting the whole system. Each unit decides whether a circulating message is relevant to it or not. Maintenance has also become easier. In short, the CAN bus is a robust, efficient, and flexible system.

Why is the CAN bus so robust ?

CAN bus is very efficient: only the strictly necessary information is transmitted. It can filter out electrical noise and electromagnetic interference. A CAN frame is structured with an identifier (like a license plate), several control bits, the actual data payload, and a robust checksum. The CAN network can be set to work at relatively high speeds, or at much lower speeds in “Fault Tolerant” mode. In this case, even if one wire breaks, communication continues using the other.

How does the CAN technology manage Errors and message Priority ?

The CAN bus also manages errors, allowing control units to communicate with each other even through error messages. It can handle priorities: the most important messages go first. Priority is decided during arbitration, when messages that start circulating at the same time “compete” until one wins. The winner is the message with the lowest identifier number. Precision is absolute, even at the level of a single bit. The signal is sampled at an exact moment to reduce the chance of reading the wrong value.

Only CAN? LIN, Flexray, MOST and Ethernet

The choice depends on needs, always keeping costs in mind. There is the LIN network, cheaper and less powerful, often used as a sub-network within a system. FlexRay and MOST are more expensive, but they allow higher transmission speed and quality. MOST, in particular, is used in infotainment systems, where it guarantees outstanding audio and video quality. Ethernet is used in vehicles for high-bandwidth applications like advanced driver-assistance systems (ADAS) to handle large amounts of data from sensors, cameras, and other ECUs.

Want to learn more about the CAN bus ?

Have a free preview at our Udemy Course