How CAN Bus/CAN FD Enables In-Vehicle Networking

The automotive industry is thriving with innovations in technology, design, UX, connectivity, infotainment, and safety solutions. To support these functionalities, behind the scene, there is a complex network of Electronic Control Units (ECU), which is powering modern-day vehicles with smart features.

Automotive ECU is an embedded hardware platform that powers complex systems in a vehicle such as actuator controls, heads-up display, ABS, telematics, infotainment systems, battery management systems and more. Modern-day vehicles have more than 70 ECUs and these ECUs communicate with each other to accurately manage a large number of vehicular functions. This is where the CAN bus system has its significance.

What is a CAN bus system?

CAN bus (controller area network) is an in-vehicle network, which facilitates communication between Electronic Control Units (ECUs), sensors, and actuators in a vehicle, without a host computer. Before CAN bus system, electronic components in a vehicle used to communicate with each other via point to point wiring, which was too complex, bulky, and inconvenient to manage. The CAN bus is a reliable, simple, and inexpensive serial bus system for in-vehicle communication.

Advantages of CAN protocol

1. Low cost and lightweight network: CAN bus protocol eliminates point-to-point wiring between electronic components in a vehicle and allows analog and digital signals to travel over a shared medium using multiplex wiring.   CAN bus allows single wire to connect with ECUs, actuators, and sensors in a vehicle and enable high-speed data transmission.  Implementation of CAN bus reduces a huge amount of complex wiring, resulting in a lower cost of the system.
2. Robustness: CAN bus systems are durable and reliable communication network with built-in failure detection mechanisms. All the nodes in the network are informed in case any failure is detected. Robust CAN bus systems are resistant to electromagnetic disturbances.
3. Flexibility: In CAN bus systems, nodes can be easily added or removed as per the requirement of the system. CAN bus protocol is a message-based protocol and transmits the data, embedded into CAN message itself. All the nodes in the system are capable of receiving all the messages transmitted on the bus, the node decides the relevance and priority of the message to discard or to accept.

CAN Bus Data Frame

• SOF- Start of Frame. The message starts from this point.
• Message Identifier: CAN 11-bit identifier, decides the priority of the message. Lower the binary value, higher the priority.
• RTR- Remote Transmission Request. RTR is dominant only when any specified node requires information.
• IDE- Single Identification Extension. Indicates a CAN identifier is transmitted without extension.
• R0- reserved bit.
• DLC- Data Length Code – 4 bits
• Data Field- Up to 64 bit of data can be transmitted.
• CRC- Cyclic Redundancy Check. 16 bit CRC checks bits for error detection.
• ACK- Acknowledge. It is 2 bit.
• EOF- end of frame. 7-bit field indicates the end of the message frame.

Evolution of CAN bus and CAN FD (Flexible Data Rate) protocol

CAN bus came into existence in the year 1986 by Bosch, it became one of the most successful network protocols of all time. Today, the CAN bus protocol has become one of the leading serial bus systems. In the 1990’s, CAN 2.0 (ISO 11898) was submitted for international standardization and later it became a standard series.

With the increase in the number of in-vehicle sensors and to support evolving automotive applications a faster communication network was required as the regular CAN bus started facing bit rate and payload limitations.  With just 1 Mbps of data transmission and a maximum payload of 8 bytes per frame, it became very difficult by classical CAN bus to manage increasingly complex ECUs and fast-paced applications like ADAS.

This is when CAN FD was introduced in 2012, which enabled data transmission rate up to 8 Mbps and allows transmission of data packets of 64 bytes, enabling faster in-vehicle communication among ECUs. CAN FD (Flexible Data rate) has multiple advantages over CAN bus protocol to support transforming vehicular needs in infotainment, power train, ADAS, and other features such as:

• Increased data transfer rate: CAN bus is a reliable bus system for in-vehicle communication. Improved data rate to support large volume data with high speed is the need of the hour in the automotive industry. Classical CAN bus with 1 Mbps data rate is unable to meet this requirement. Whereas, CAN with flexible data rate (FD) supports data transfer up to 8 Mbps.
• Supports larger data payloads: Larger payloads implies increased data length as compared to the classical CAN bus. CAN FD supports up to 64 bytes/message. The larger payload carrying capacity leads to improved bus efficiency in terms of faster and efficient in-vehicle communication among ECUs.
• Improved reliability: CAN FD uses Cyclic Redundancy Check to detect errors in the bus. Classical CAN bus has a weakness of not addressing the issue of CRC (Cyclic Redundancy Check) flawlessly, resulting in unaddressed and stuffed bit errors in the bus. CAN FD eliminates this issue by including dynamic stuff bits and makes CAN FD a more reliable network for vehicular applications.
• Improved security in cars: Security breach in CAN bus protocol can lead to serious implications, as hackers can manipulate data traffic and access nodes to hamper in-vehicle connectivity. CAN FD with increased bandwidth and suitable encryption methods allows only authenticated devices to access the serial bus and provide secure data traffic in cars.

The future of automotive will be V2X connectivity, autonomous or self-driving cars, and electric vehicles, which will demand vehicle’s highly complex electrical and electronics architecture to communicate with each other. CAN FD with its ability to support higher bandwidth will meet the future requirements of the automotive industry.

eInfochips as an automotive IoT solution provider assists automotive companies to design in-vehicle and automotive communication protocol like CAN and CAN FD to assist power train, body control module, infotainment, ADAS, etc. Know More on Automotive IoT Solutions.