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Olga Weis
Last updated Jul 16, 2024
Modern vehicles rely heavily on electronic systems for efficient operation and safety. At the heart of these systems is the Controller Area Network (CAN) bus system, a robust and efficient communication network. This article delves into the fundamentals of CAN bus systems, their workings, and their significance in the automotive industry.
The acronym CAN stands for Controller Area Network. CANs are used to establish communication between microcontrollers in a network or bus. CANs are comparable to Ethernet or LANs which provide a standard method for computer-to-computer communication.
A CAN offers a simplified method of providing electronic controls over the systems that had been used previously. Implementing a CAN bus enables auto manufacturers to make a substantial reduction in the amount of wiring in each automobile.
The main line called the “backbone" forms the foundation of a CAN bus system. The backbone connects all microcontrollers in a vehicle and provides information to a centralized primary controller responsible for monitoring all electronic systems. This configuration simplifies identifying potential faults and investigating and resolving an error without querying multiple subsystems placed throughout an automobile.
A CAN bus system minimizes possible failure points and consolidates communication by sending data over a single line. It eliminates any concerns over multiple connection failures causing problems that are hard to identify. The enhanced redundancy of a CAN bus improves reliability by allowing the main system to remain operational even if subsystems fail. This redundancy was impossible to implement with discrete controllers.
A CAN bus line is constructed using a twisted pair of wires that have a 120 ohms terminating resistor on each end. One wire is designated as CAN High with the other named CAN low. All devices connected to the bus are known as electronic control units (ECUs) or nodes.
ECUs can play a variety of roles in an automotive CAN bus system. Nodes can serve as control units for the engine, headlights, air conditioner, airbags, and other systems necessary for the vehicle’s operation. Modern autos may have up to 70 ECUs that need to transmit and share data with other nodes.
Each node consists at a minimum of a CAN controller and an embedded microcontroller. Digital data is converted into messages on the bus by the CAN controller. The CAN controller accepts information, translates it, and sends it to another CAN controller.
The embedded microcontroller processes data and performs tasks such as turning on a light inside the car or lowering a window. Microcontrollers can control the flow of information to the dashboard in response to a message generated by the CAN controller.
These two diagrams illustrate how nodes communicate with each other and exchange data with and without the CAN protocol and CAN bus system.
When using the CAN bus, a single ECU can transmit data to all other ECUs connected to the system. Those ECUs can review the information and choose to receive or ignore it.
A CAN bus enables communication using two wires: CAN low (CAN L) and CAN high (CAN H). The data link layer of the CAN bus is described by ISO 11898-1 with the physical layer described by ISO 11898-2.
The physical layer of a CAN bus is comprised of cables, cable impedance, electrical signal levels, node requirements, and other items required for the network’s operation.
ISO 11898-2 describes the specifications for items in the physical layer like cable length, cable termination, and baud rate. Following are some examples of these specifications.
🔹 Each end of the CAN bus needs to be terminated with a 120 Ohms CAN bus resistor
🔹 CAN nodes require connections using two wires with baud rates up to 1 Mbit/s (CAN) or 5 Mbit/s (CAN FD)
🔹 Cable length for a CAN Bus can be 40 meters at 1 Mbit/s or 500 meters at 125 Kbit/s
Several different types of networks can be implemented with a CAN bus.
🔹 Slow speed CAN bus is also called a fault-tolerant CAN.
🔹 Each node has a CAN termination
🔹 The low-speed CAN bus supports baud rates of between 40 and 125 Kbit/s
🔹 Communication can continue even if there is a fault in one of the wires
🔹 Simple calling is a feature of a high-speed CAN bus
🔹 This type of network is the one most commonly used by today’s automobile manufacturers
🔹 Baud rates of between 40 Kbit/s and 1 Mbit/s are supported
🔹 The high-speed CAN bus forms the foundation of higher-layer protocols like CANopen, j1939, and OBD2
🔹 A LIN bus is a low-cost alternative that employs fewer harnesses
🔹 Less expensive nodes are used in a LIN bus
🔹 The network provides functionality for door locks and air conditioning
🔹 Network configuration is typically comprised of a LIN bus master acting as the gateway for up to 16 slave node
🔹 CAN FDs are deployed in high-performance vehicles
🔹 The CAN FD protocol is an extension of the original CAN protocol and was released by Bosch in 2012 to address the need for increased data transfer speeds
🔹 Automotive Ethernet supports higher data transfer rates than a CAN bus
🔹 This network does not have the security features of CAN and CAN FD
🔹 The automotive industry is adopting this network and it will be implemented in modern cars and trucks.
🔹 Automotive ethernet supports the increased bandwidth required to implement systems such as onboard cameras, Advanced Driver Assistance Systems (ADAS), a fleet management system, and other features that require high-speed data transfer
Implementing CAN bus technology enables automobile manufacturers to deploy On-Board Diagnostics protocols. These protocols offer standardized problem codes that mechanics can easily interpret for problem resolution. Data ports in the CAN bus are used to introduce software updates to onboard systems and computers.
Some popular protocols used to provide advanced automotive features include:
🔹 OBD-II On-board diagnostics (OBD, ISO 15765) furnishes mechanics with diagnostic and reporting features to save time when identifying vehicle issues
🔹 J1939 is the standard network for heavy-duty vehicles like trucks and buses
🔹 CAN FD extends the original CAN data link layer and enables an increased payload from 8 to 64 bytes. It can also provide higher bit rates based on the CAN transceiver employed
🔹 CANopen is implemented in applications that feature embedded controls such as industrial automation facilities
The CAN bus protocol will remain important in the coming years. However, the following major trends will directly influence it:
🔹 The growing use of autonomous vehicles/self-driving cars
🔹 Increasing need for more advanced vehicle functionalities
🔹 Developing more advanced cloud technologies, such as cloud-based fleet management systems
🔹 Increasing integration of the Internet of Things (IoT) and connected vehicles
It’s also worth noting that the improvement of vehicle-to-network (V2N) technology and cloud computing is predicted to cause telematics to grow rapidly. This growth also includes IoT devices such as CAN IoT recorders.
