CAN XL protocol is an extension of the CAN protocol outlined in ISO 11898-1, and is developed by CAN in Automation (CiA). This enhancement targets an ambitious goal of increasing the bandwidth capabilities of CAN to over 10 Mbit per second. This evolution in CAN addresses the growing demands of the electric vehicle and autonomous systems industries, opening up new possibilities for signal-based communication buses.
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Signal Integrity: CAN XL SIC Transceiver
To mitigate potential challenges associated with higher bit-rates, the Special Interest Group introduced the CAN XL Signal Improvement Capability (SIC) Transceiver. With this innovative solution, CAN XL enhances communication robustness on physically demanding topologies.
The SIC transceiver provides symmetrical signal transitions, reduces ringing and reflections on the bus, and enables reliable communication over longer cable lengths. It ensures deterministic latency by supporting non-return-to-zero (NRZ) encoding and precise voltage swing levels to differentiate dominant and recessive states at high speeds.
High Bandwidth and Payload Flexibility in CAN XL Protocol
CAN XL supports larger payloads of up to 2048 bytes, compared to the 64 bytes offered by CAN FD. This allows the tunneling of Ethernet frames and other large data structures directly over CAN XL without fragmentation. This capability is essential for applications involving firmware over-the-air (FOTA) updates or complex sensor fusion data transfers.
The Data Phase Bit Rate (DPBR) of CAN XL can exceed 20 Mbit per second, depending on transceiver and physical layer characteristics. This extended data rate aligns CAN XL closer to automotive Ethernet performance while retaining the benefits of arbitration and broadcast features inherent in CAN.
Protocol Stack and Data Link Layer Enhancements
CAN XL introduces a two-part frame format consisting of a Header Segment and a Data Segment. The header includes a new XL Format (XLF) indicator bit, allowing mixed CAN XL and CAN FD traffic on the same bus. A Cyclic Redundancy Check (CRC) field based on CRC-32Q ensures enhanced error detection capabilities for large frames.
It also implements a Security Protocol Identifier (SecID) field, allowing selective application of message authentication or encryption mechanisms. This makes CAN XL more suitable for cybersecurity-relevant automotive applications.
Backward Compatibility of CAN XL Protocol
Much like its predecessor, CAN FD, CAN XL is designed with backward compatibility in mind, allowing seamless access to both CAN FD and Classical CAN protocols. While a CAN FD node cannot directly receive a CAN XL message, it will not register an error and will participate in arbitration on the subsequent frame.
This dual usage of CAN FD and CAN XL on the same bus is made possible by leveraging CAN FD’s Protocol Exception State. This state is activated when the recessive XLF bit of a CAN XL message sets the CAN FD node into the Protocol Exception State, a safeguard introduced in the CAN FD specification (ISO 11898-1:2015) for future expansions.
Layered Protocol Architecture and Multiplexing
CAN XL enables multiple higher-layer protocols (HLPs) to co-exist on a single bus using a Type Field in the XL Header. This field allows different HLPs such as SOME/IP, UDS, or Diagnostic over IP to be multiplexed and interpreted appropriately at the receiver end.
Furthermore, CAN XL supports Time-Triggered Communication by enabling frame preemption and prioritization. This is critical for applications requiring real-time communication, such as brake-by-wire and steer-by-wire systems.
Tooling and Development Ecosystem
Leading tool providers such as Vector, ETAS, and Peak-System have begun incorporating CAN XL into their simulation and test tools. Support for bus analyzers, protocol stacks, and communication matrices (e.g., in AUTOSAR COM) is steadily expanding.
Model-based development environments now include support for CAN XL parameter configuration, bit timing calculations, and compliance with ISO 11898-1:2024. These tools assist engineers in configuring nodes with precise transceiver delay compensation and bit timing tolerances.
Real-World Applications of CAN XL Protocol
Several OEMs and Tier-1 suppliers are already evaluating CAN XL for deployment in zonal E/E architectures, where central vehicle controllers communicate with local gateways. The protocol’s high data rates, reliability, and compatibility with existing CAN infrastructure make it attractive for cost-sensitive and safety-critical automotive domains.
With the addition of PHY layer options, including twisted pair and coaxial cables, CAN XL is being tailored for scalable deployment in ADAS, battery management systems, and central compute units.