Physikalische Schicht bei CAN – Status und Zukunft
CAN in Automation
Classical CAN is still the most used CAN data link layer protocol. This will continue in the next couple of years. Step-by-step, Classical CAN in-vehicle networks will be substituted by CAN FD networks. CAN FD is an improvement of the well-established CAN protocol to increase the bit rate up to 5 Mbit/s and the payload up to 64 bytes in CAN networks and is set for the next generation of passenger cars. The truck industry and non-automotive application are also migrating to CAN FD. Since the end of 2018, engineers from the CAN community started discussing the features for the next generation of a CAN-based protocol that is named CAN XL. CAN XL provides an extra large payload of 2048 bytes, and supporting in the data-phase bit rates exceeding 8 Mbit/s, to fill the gap between CAN FD and Ethernet.
The CAN physical layer is divided into three parts: The physical coding (PCS) implemented in the CAN controller chips, the physical media attachment (PMA) specifying the transceiver characteristics, and the physical media-dependent sub-layers (PMS). The PMS is application-specific and is not generally standardized.
With the development of the data link layer protocol from Classical CAN, CAN FD to CAN XL, the requirements of the protocols have impacts on physical layer. For example, to use the accelerated bit rates of CAN FD, new parameters and requirements are specified, as loop delay symmetry, etc. They are specified in ISO 11898-2:2016 and CiA 601 series. For CAN XL protocol one significant requirement is that there are no error frames during data phase. This improves the possibility to suppress or avoid signal ringing and allows the possibility of new transmitter concepts in data phase. In arbitration phase wired or concept is needed like in ISO11898-2. Additionally, higher bit rates are needed to transmit the lengthened frame of 2048 bytes. The target is 10 Mbit/s or even higher.
This presentation will introduce the development of the CAN protocols, CAN FD and CAN XL, and the impacts on CAN physical layer. Another topic is the status and future of the interoperability of the CAN transceivers during the development. For example, the in CiA 601-4 specified CAN FD-SIC (signal improvement capability) transceiver could also support CAN XL protocol. The system integrator may choose the most fitting CAN physical layer concept for their application, in consideration of payload length, max. bit rate, error signaling, and topology dimension, etc.