CAN FD: Review and preview

CAN with flexible data-rate, known as CAN FD, has passed the first level of ISO balloting in summer 2014.

Unfortunately, some weaknesses in the data link layer protocol have been detected after the ISO voting. In the meantime, the CAN FD experts have fixed them by introducing a stuff-bit counter and other protocol improvements (see also Bosch’s whitepaper). The changes in the CAN FD protocol are user-transparent, meaning the changes have nearly no impact on the usage. Therefore, the software and system development of CAN FD applications is not delayed. But the chipmakers need to provide new CAN FD hardware. For FPGA implementations this is quite easy to do, but the micro-controller manufacturers have to do eventually a complete redesign. This may lead to some delay in the availability of micro-controllers featuring CAN FD. “The year of 2014 was somehow challenging for the CAN FD community,” said Holger Zeltwanger, CiA Managing Director. “But it is better to detect problems before the serial production has started.” In the year of 2015, ISO will hopefully release the next version of ISO 11898-1 standard and the related conformance test plan (ISO 16845-1), which includes the CAN FD protocol. It is also planned to finalize the next version of ISO 11898-2, the high-speed CAN transceiver standard. It will merge the definitions, which were in the previous ISO 11898-2 standard as well as in ISO 11898-5 (low-power mode) and in ISO 11898-6 (selective wake-up procedure). This harmonized standard will support bit-rates higher than 1 Mbit/s as used in the data-phase of the CAN FD protocol. CiA will organize further CAN FD plug fest in Germany and USA, in order to prove the interoperability of CAN FD chips and modules. During plug fest also the limits of different network topologies will be tested. The results will be introduced into the CiA 601 series of CAN FD system design specifications and recommendations. In addition, CiA is going to develop CAN FD related specifications for commercial trucks (physical layer and application layer) in the series CiA 602. In spring 2015, the CiA Special Interest Group (SIG) CANopen application layer will release the CiA 301 version 5.0, which will support the CAN FD data link layer. esides the higher throughput, the payload per data frame is increased to 64 byte instead of 8 byte provided in Classical CAN. “CiA supports the substitution of Classical CAN by CAN FD enabled hardware,” said Holger Zeltwanger,” so that in a couple of years all new products support CAN FD independent if the users requires the higher bit-rate and the longer data frames.” CAN FD will be as reasonable in price as Classical CAN was. Additionally, the power consumption is lower as in other communication technologies and the robustness is much higher. The reliability of the CAN FD protocol is even better than Classical CAN, which was already better compared to other commercially available networks. The simplicity of the CAN FD protocol usage is the same as of Classic CAN. But the system designer needs to respect more than in the past the general electrical design rules, due to the higher bit-rate (up to 8 Mbit/s) during the data-phase. CiA plans a series of Tech Days all over the world informing interested parties with first-hand information about the CAN FD technology.