The non-profit association CiA (CAN in Automation) published document CiA 610-1 as a draft specification proposal (DSP). This document specifies the CAN XL data link layer (DLL) and the physical encoding sublayer (PCS).
The third generation of CAN protocols provide a data field length of 1 to 2048 bytes. It is designed as a backbone network or backbone subnet, which can be integrated into TCP / IP environments. CAN XL has a true Hamming distance of 6, which means that five randomly distributed bit errors can be detected. This is achieved by means of two CRC fields in the Protocol Data Unit (PDU).
The novelty is the separation of the 11-bit priority field and the 32-bit acceptance field. In Classic CAN and CAN FD, the 11-bit or 29-bit identifier field has two functions: single priority to access the network and indication of the content of the data field. CAN XL provides several built-in upper layer configuration information: SDU (Service Data Unit) type allows running heterogeneous upper layer protocols, and VCID (Virtual CAN Network ID) supports protocol instances of top layer. These features are similar to Ethernet-based features, CiA explained.
The physical signaling sublayer provides optional PWM (Pulse Width Modulation) coding allowing rates greater than 10 Mbit / s. The error message can be deactivated. In this case, the upper layers should report the XL frames that were not correctly received. An optional frame fragmentation is under development as well as frame security (CADsec).
âCAN XL is a reliable and robust approach to the bottom layer at a very reasonable cost,â said Holger Zeltwanger, CEO of CiA. âThe seamless integration into TCP / IP network systems makes CAN XL very suitable for high volume subnets in passenger cars as well as for other areas of application. “
CiA also specifies the tunneling of Ethernet frames via CAN XL frames. The second plugfest has been postponed due to the current fourth wave of Covid-19 in Germany. The first one took place in summer, test the interoperability of the different implementations. All tests passed, CiA said. During the next plugfest, errors will be injected and the correct behavior will be tested. âCAN XL is designed for price sensitive applications, which require reliable and robust communication, not just in on-road vehicles,â Zeltwanger said. “We will submit the CAN XL specification to ISO for integration into ISO 11898-1, which is under review.”