The controller area network, or CAN bus protocol, ushered in a new era of automotive technology. It created the communications framework that allows for anti-lock braking systems, power windows, and improved cruise control, among many other features. The success of these features and the desire for more advanced technology in automobiles has led to the modern connected vehicle, sporting functionalities such as advanced driver assistance systems, connected head units, and in-vehicle Wi-Fi.
CAN FD comes with a high-performance algorithm, which expands CAN’s ability to hold data. (Image source: Kvaser)
CAN remains a standard in automobiles up to the present day. Its flexibility and ease of use have helped to secure its continued use, even as vehicular technology continues to make huge leaps. While Ethernet and FlexRay networks handle the most data-intensive tasks, the CAN bus protocol takes care of safety-critical features, such as powertrains, power steering, and anything requiring hard real-time control. Advances in CAN make it an even more valuable element of the modern connected car.
Introduction to CAN FD
CAN FD was developed in 2011 by Robert Bosch GmbH as an extension to the original CAN protocol. Bosch worked closely with carmakers and other CAN experts, coming together to respond to the need for a more powerful CAN protocol. The “FD” in CAN FD means “flexible data-rate,” which is the big advancement here, allowing increased performance and higher bandwidth communication.
Benefits of Moving to CAN FD
There are a number of ways in which CAN FD sets itself apart from classical CAN. The three most powerful ways in which CAN FD provides added value are:
- CAN FD provides shorter CAN frames while increasing the bit rate. This provides for lower latency, better real-time performance, and higher bandwidth.
- CAN FD can hold more data in the CAN frame: from 8 to 64 bytes. With less relative overhead, you can expect better data throughput. When sending large data objects, you can rely on simpler, more efficient software.
- CAN FD has a higher-performance CRC algorithm, lowering the risk of undetected errors.
The increased performance and bandwidth of data communication makes CAN FD an ideal middle ground between classic CAN and the more complex communication protocols being implemented in modern vehicles, such as FlexRay and Ethernet.
While not widely implemented yet, CAN FD is in active development with several large car makers. The two major areas that are most affected by the advances of CAN FD are real-time messaging and physical layer engineering.
The CAN Real-Time Expert
For the CAN real-time expert, CAN FD can dramatically change the real-time performance of a system in three main ways:
- CAN FD allows data to be sent at a higher bit rate. This makes all of the CAN frames much shorter in time, thus lowering the response time.
- It is possible to increase the data load above 8 bytes, up to 64 bytes. In this way, CAN frames that are almost eight times longer than classical CAN frames are produced. The downside is that the increased data load causes longer delays between CAN frames (though this can be compensated for by using a higher bit rate).
- There are more overhead bits in CAN FD so that even with less than 8 bytes of data, CAN FD frames are longer than classical CAN frames.
The Physical Layer Engineer
For physical layer engineers, CAN FD is identical to classical CAN as long as there are no demands to increase the bit rate in the data section. If there is a need to increase the bit rate, the cables will need to be higher quality and measurements will need to be taken at different points along the CAN bus wires to ensure that the signal is square. CAN FD also requires continuous impedance throughout the CAN wires in order to function properly at higher bit rates.
A Flexible Choice for Future Automotive Development
The CAN bus has always been prized for its elegant simplicity and flexibility. With greater complexity of computing in new vehicles, CAN FD provides the simple flexibility of CAN, but with a much wider capacity. While it requires some adjustments in physical layer engineering and real-time configuration, the payout of up to eight times the bit rate will persuade people to convert.
Jesse Paliotto is the Marketing Director at Kvaser AB, a Swedish electronics company specializing in advanced Controller Area Network (CAN) solutions. He has worked in media technology, communications, and sales, with an educational background in marketing strategy. Jesse resides in Los Angeles, Calif.