From CAN CC via CAN FD to CAN XL

The development of CAN began with the classic CAN protocol, which, with data rates of up to 1 Mbit/s and a maximum of eight data bytes per frame, served as the standard for many years. With the introduction of CAN FD, up to 64 data bytes could be transmitted for the first time, supplemented by flexible bit rate switching in the data field with speeds of up to eight Mbit/s. CAN XL consistently continues this evolution: The new protocol allows up to 2,048 data bytes per frame and data rates of up to 20 Mbit/s in mode-switching operation. It thus closes the gap between classic fieldbus systems and modern, IP-based communication architectures.

Structure and functionality of CAN XL

The key innovation lies in the so-called XL Frame Format (XLFF), which extends the familiar basic structure with CAN ID, data length, and data bytes with additional fields. The 11-bit Priority Identifier (PID) remains as a replacement for the classic CAN frame identifier and is used for prioritization in the arbitration phase of CAN frames. The CAN frame identifier has been moved to the dedicated Acceptance Field. More on this later.

The Service Data Unit Type (SDT) defines the type of information being transported, for example, for the use of CAN FD tunneling. Another distinguishing feature is the Simple/Extended Content Bit (SEC), which indicates the use of additional headers in the data field, for example, for encryption or fragmentation. The Data Length Code (DLC) fields describe lengths of up to 2,048 bytes, allowing significantly larger amounts of data to be transported per frame than with previous CAN generations. This reduces the overhead in frames and in communication overall.
The Virtual CAN Network ID (VCID) plays a special role, allowing frames to be assigned to virtual networks. This allows for the logical segmentation of networks, similar to VLANs in Ethernet, and supports modern zone-based vehicle architectures. In addition, the Acceptance Field (AF) enables flexible filtering and message mapping, for example, when tunneling traditional CAN data. Transmission is secured by additional CRC fields, which ensure the integrity of both the protocol header and the entire frame.

Cabling and SIC transceivers

A key feature of CAN XL is its use of existing physical infrastructure. As with CAN Classic and CAN FD, the system is based on a bus with CAN High and CAN Low lines, typically implemented in a line topology with two 120 ohm terminations. This significantly simplifies migration, as existing wiring harnesses can be reused in many cases.

Figure 1: Typical CAN-XL cabling.

Another aspect is so-called mode switching, which allows switching to specialized signal transmissions in XL mode to achieve data rates of up to 20 Mbps. The signal's voltage swing is reduced to one volt, and state changes to CAN High and CAN Low are performed using a push-pull method. While classic error frames are limited in this fast mode, reliable communication is ensured by the extended CRC fields. CAN XL thus combines the advantages of a high data rate with the robustness of the familiar physical transmission layer. The switch to fast mode occurs for the data portion of the frame, similar to CAN FD.

Figure 2: Mode switching enables high data rates with high robustness. Additional fields in the CAN XL frame provide structured meta-information for processing in higher protocol layers.

CAN XL in the spotlight: advantages and challenges

The key advantages of CAN XL lie in its combination of high data capacity and backward compatibility. With up to 2,048 bytes per frame, not only sensor data but also IP packets can be transmitted efficiently. At the same time, existing CAN infrastructures can be utilized, enabling mixed environments with Classic, FD, and XL. Particularly valuable for the future is the ability to create virtual networks with VCID and thus implement zonal architectures that enable load balancing and targeted quality assurance of data traffic.

However, this expanded functionality also presents challenges. The complexity of protocol evaluation increases, and for high bit rates above 8 Mbps, mode switching is necessary, which limits traditional mechanisms such as error frames. The communication standard for CAN XL (ISO 11898-1:2024) has been specified, so OEMs and suppliers can now begin practical implementation and integration into existing architectures.

CAN XL or Automotive Ethernet? A Comparison

Compared to Automotive Ethernet, CAN XL represents an intermediate stage between traditional bus systems and high-speed networks. While CAN XL enables data rates of up to 20 Mbit/s, Ethernet in the automotive sector currently achieves up to 10 Gbit/s. CAN XL offers a significantly larger payload than previous CAN systems, with up to 2,048 bytes, while Ethernet typically has a maximum packet size of 1,500 bytes. Both technologies rely on twisted pair cables but differ in their topology: CAN XL continues to favor line structures with smaller stars, while Ethernet operates in star, tree, or ring architectures. While Ethernet is primarily used for high-bandwidth applications such as infotainment or central backbones, CAN XL is particularly suitable for zonal architectures, sensor data processing, and the integration of existing CAN environments.

Table 1: CAN XL compared with Automotive Ethernet.



Application areas of CAN XL

A key application area for CAN XL is the implementation of zonal architectures, where control units are no longer connected in a star configuration to a central ECU, but communicate within functional zones and forward their data in aggregated form. This reduces cabling effort and supports modular vehicle concepts. CAN XL can also play an important role as a transport medium for CAN FD messages or IP-based data, replacing or supplementing gateways. Particularly in the areas of driver assistance systems and sensor fusion, the advantages of large payloads can be utilized to efficiently and reliably consolidate sensor data and forward it to central processing units.

The solution from PEAK-System: CAN XL Starter Bundle

PEAK-System responded early to the introduction of CAN XL and, with the CAN XL Starter Bundle, offers a comprehensive solution for developers, testers, and integrators. In addition to the PCAN-USB XL USB-CAN interface, which supports mode switching and is backward compatible with CAN FD and CAN Classic, the bundle also includes the necessary transceiver technology and the PCAN-Basic API for software integration. This not only gives users the opportunity to test CAN XL in mixed environments but also provides practical access to analysis tools and development environments. The Starter Bundle thus provides the ideal starting point for exploring the possibilities of CAN XL in real projects and developing future-proof communication architectures.

More information about the Starter Bundle