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Evolution of CAN FD in Automotives

By the time the automobile industry entered into advancement, CAN bus had started to rule the industry with the wide range of functionality it could offer. It had so many good features at a very reasonable cost that it soon became the core communication protocol to be used. But, with time, technological developments outgrew CAN's ability to function. The growing number of technologically superior electronics modules that called for continuously rising data required more flexible support. The then so extensive list of features started falling short, and this demanded a solution. Also, with this explosion in data and bandwidth needs, just increasing more Can wires was not an option. So, as a solution, in 2011-2012, Bosch developed and released an extension to the original CAN-Bus protocol known as CAN Flexible Data rate (specified in ISO 11898-1:2015).

CAN FD is practically a more capable CAN. Flexible signal transmission provided automotive electronics' communication with increased bandwidth and all the required functionality very cost-effectively. Moreover, it offers upgradation to almost every feature CAN hold and is a better alternative for more advanced needs of data and bandwidth requirements.

The classical CAN 2.0 bus has many features that make it an ideal choice for application where the number of ECU's is more, and the bandwidth utilization is less. Classical CAN bus supports a maximum message payload of 8 bytes per frame at a maximum data rate of 1Mbps. Also, standard/extended CAN 2.0A allows 11Bit/29Bit data transmission, respectively. Whereas CAN FD supports a flexible message payload, ranging from 0, 8, 12, 16, 20, 24, 32, 48, 64 bytes per frame at 2, 5 and 8 Mbps of data rates.

Looking at the Frame Formats for classical CAN Bus and CAN FD, they may not seem very different. But there are a few added fields in a CAN FD frame format that are not present in classical CAN bus.

RRS: Remote Request Substitution (always a dominant 0). The remote frames are not at all supported in CAN FD. (In classical CAN, there is RTR (Remote Transmission Request) for identifying the data frames and remote frames)

FDF: Flexible Data Rate Format (always a recessive 1) used to indicate Flexible data frame format usage.

EDL: Extended Data Length (always a recessive 1) for managing larger payloads and faster bit-rates in CAN FD.

BRS: Bit Rate Switch helps determine the bit rate of a data frame.

  • Dominant 0 signifies that the arbitrat