CiA 610-1 and CiA 610-3

CiA has released the CiA 610-1 and the CiA 610-3 documents as Draft Specification Proposal (DSP). They specify the CAN XL lower layers.

CAN XL, the third generation of CAN technology, provides a data field length of 1 to 2048 byte. It is intended as backbone or sub-backbone network, which can be easily integrated into TCP/IP environments. The CAN XL protocol features a true Hamming distance of 6 meaning five randomly distributed bit errors can be detected. This is achieved by means of two CRC fields in the protocol data unit (PDU). New is the separation of the 11-bit priority field and the 32-bit acceptance field. In Classical CAN and CAN FD, the 11-bit or 29-bit identifier field has two functions: unique priority to access the network and indication of the data field content. CAN XL provides several embedded higher-layer configuration information: the SDU (service data unit) type allows to run heterogenous higher-layer protocols and the VCID (virtual CAN network ID) supports to instance higher-layer protocols. These features are similar to Ethernet-based functions.

Physical coding and medium attachment unit sub-layers

The physical coding sub-layer (PCS) features an optional PWM (pulse-width modulation) coding allowing bit rates of higher than 10 Mbit/s. CiA 610-3 specifies the corresponding medium attachment unit (MAU) sub-layer. CAN SIC (signal improvement capability) XL transceivers have already been tested in the CAN XL plugfest mid of 2021. The switching from the arbitration bit rate (max.: 1 Mbit/s) to the data phase bit rate (10 Mbit/s and more) is performed after the network arbitration, when only one CAN XL node is allowed to transmit. The switching back to arbitration bit rate is done before the Acknowledgement field, when all CAN XL nodes confirm the correct reception of the received CAN XL data frame.

CAN XL nodes can also use classic high-speed transceivers with and without SIC functionality, but then the data phase bit rate of 10 Mbit/s is not possible. Classic CAN high-speed transceivers are standardized in ISO 11898-2 and CAN SIC transceivers are specified in CiA 601-4. CiA is going to submit the CiA 610-3 specification to be included in the ISO 11898-2 standard, which is currently under review.
Reliable and robust

The error signaling of the CAN XL data link layer (DLL) can be switched off. In this case, higher layers should signal not correctly received XL frames. An optional frame fragmentation is under development as well as a frame security (CADsec).

“CAN XL is a reliable and robust lower-layer approach at very reasonable costs,” said Holger Zeltwanger, CiA Managing Director. “The seamless integration into TCP/IP network systems makes CAN XL very suitable for high-volume sub-networks in passenger cars as well as other application fields.” CiA also specifies the tunneling of Ethernet frames via CAN XL frames.

The second plugfest was postponed due to the current fourth Covid-19 wave in Germany. The first one took place in summer testing the interoperability of different implementations. All tests were passed successfully. In the next plugfest, errors will be injected and the correct behavior will be tested. “CAN XL is made for price-sensitive applications, which require a reliable and robust communication as needed not only in road vehicles,” stated Zeltwanger. “We will submit the CAN XL specification to ISO for integration into the ISO 11898-1 standard, which is under revision.”