The Controller Area Network (CAN bus) is explained for dummies in this tutorial, including message interpretation, CAN logging, and the link to OBD2, J1939, and CANopen.
You can also watch our CAN bus protocol introduction (with over 600,000 views on YouTube) above.
What exactly is a CAN bus?
The Controller Area Network (CAN bus) is the networking system’s nervous system.
The CAN bus connects ‘nodes’ or ‘electronic control units’ (ECUs), which are similar to body parts. One part’s sensed data can be exchanged with another.
So, what exactly is an ECU?
Engine control units, airbags, audio systems, and other ECUs can all be included in an automotive CAN bus configuration. A modern car can contain up to 70 ECUs, each of which may contain data that must be shared with other sections of the network.
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The CAN norm comes in handy in this situation:
Each ECU can communicate with all other ECUs using the CAN bus system, which eliminates the need for complex dedicated wiring.
Specifically, an ECU may use the CAN bus to prepare and broadcast information (such as sensor data) (consisting of two wires, CAN low and CAN high). All other ECUs on the CAN network accept the broadcasted data, and each ECU can then review the data and determine whether to receive or ignore it.
Physical layer of the CAN bus
A data link layer and a physical layer define the controller area network in more technical terms. ISO 11898-1 describes the data link layer, while ISO 11898-2 describes the physical layer in high-speed CAN.
The physical layer of the CAN bus specifies things like cable types, electrical signal levels, node specifications, and cable impedance, among other things. The ISO 11898-2 standard, for example, specifies the following:
CAN nodes must be connected via a two-wire bus with baud rates of up to 1 Mbit/s (Classical CAN) or 5 Mbit/s (Advanced CAN) (CAN FD)
Length of cable: The maximum length of a CAN cable should be between 500 metres (125 kbit/s) and 40 metres (1 megabit/s).
Termination: At each end of the CAN bus, a 120 Ohms CAN bus termination resistor must be used to properly terminate the bus.
CAN bus, LIN bus, high-speed CAN, low-speed CAN,…
You’ll often come across a variety of network types in the sense of automotive vehicle networks. Here’s a quick rundown of what’s going on:
High-speed CAN bus: This article focuses on high-speed CAN buses (ISO 11898). It is by far the most widely used CAN physical layer standard, with bit rates ranging from 40 kbit/s to 1 Mbit/s (Classical CAN). It allows for easy cabling and is currently used in almost all automotive applications. It’s also the foundation for higher-layer protocols like OBD2, J1939, NMEA 2000, and CANopen. CAN FD stands for the second generation of CAN (CAN with Flexible Data-rate)
CAN bus at a low speed: This standard supports bit rates of 40 kbit/s to 125 kbit/s and allows CAN bus communication to continue even if one of the two wires is damaged – hence the term “fault tolerant CAN.” Each CAN node in this framework has its own CAN termination.
LIN (Local Intercity Network) bus: With fewer harness and cheaper nodes, LIN bus is a lower-cost supplement to CAN bus networks. A LIN master acts as a portal, and up to 16 slave nodes make up a LIN bus cluster. Non-critical vehicle functions such as air conditioning, door accessibility, and so on are typical use cases – for more details, see our LIN bus intro or LIN bus data logger articles.
Ethernet in automobiles: This is increasingly being used in the automotive industry to meet the high bandwidth demands of ADAS (Advanced Driver Assistance Systems), infotainment systems, and cameras, among other things. Compared to CAN bus, automotive ethernet provides significantly faster data transfer speeds, but it lacks some of the protection and performance features of Classical CAN and CAN FD. Both automotive ethernet, CAN FD, and CAN XL will most likely be used in modern automotive and industrial production in the coming years.