As an upgraded version of the CAN bus, CAN FD (CAN with Flexible Data rate) has significantly expanded and enhanced in terms of data length and bandwidth to meet the high-speed communication demands of industrial and automotive applications. In the industrial sector, CAN FD is increasingly being applied to scenarios such as industrial control and industrial communication.

Features and Considerations of CAN FD

Compared to the traditional CAN protocol, the two most significant features of CAN FD are the adoption of variable rates and a maximum of 64 bytes of data per frame. By supporting up to 64 data bytes per data frame, as opposed to the traditional CAN's 8 data bytes, it reduces the protocol overhead for the same data transmission and improves transmission efficiency.

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The variable rate is specifically manifested by the first control bit of CAN FD changing from RTR in traditional CAN to RRS, which is always dominant (0). The third control bit, which was reserved in traditional CAN, becomes FDF in CAN FD, and is recessive (1). With this design, from the BRS bit in the control segment to before the ACK segment (including the CRC delimiter), CAN FD operates at a variable rate (theoretically up to 12Mb/s), while the rest operates at the rate used by the original CAN bus.

Upgrading from CAN to CAN FD involves some additional bit fields, such as the aforementioned FDF bit, BRS bit, and ESI bit. The ESI bit stands for Error State Indicator and is used to indicate the error state of the transmitting node. When the ESI bit is dominant, it signifies that the transmitting node is in an active error state; when recessive, it indicates a passive error state.

Although CAN FD is backward compatible with traditional CAN, there are some details to consider when upgrading traditional CAN applications to CAN FD applications. For example, the impact of sampling points on communication, when upgrading from a traditional CAN network topology to a CAN FD network topology, both the software and hardware of the nodes need to change, and transceivers and controllers must be selected to correspond with CAN FD. In the controller, after the network topology has added CAN FD nodes, at least two communication CAN FD nodes are required. With the addition of CAN FD nodes, Classic CAN nodes need to set the filtering function for CAN ID to avoid erroneous frames.

Another common issue is the coexistence of traditional CAN and CAN FD. For the foreseeable future, CAN networks will likely continue to have both traditional CAN and CAN FD operating side by side. This part requires addressing the rate switching issue, with nodes that demand high real-time performance adopting CAN FD first, while other nodes with less real-time requirements will continue to use traditional CAN. In such a network topology, communication can be entirely forwarded by a CAN FD router, as the CAN FD protocol is backward compatible with traditional CAN.

Industrial Applications of CAN FD

In the industrial field, CAN FD communication is used to connect various industrial equipment and sensors. With high-speed data transmission, it is possible to monitor the operational status of equipment in real-time, improving production and maintenance efficiency. Currently, CAN FD has a comprehensive range of products and solutions supported in the industrial sector.

Firstly, there is a wide selection of MCUs with CAN FD interfaces, whether from international giants such as Texas Instruments, Renesas, Infineon, and NXP, or domestic manufacturers like Saiyuan Micro, Lingdong Micro, and GigaDevice, all offer MCUs with CAN FD interfaces to meet the broad application needs in the industrial field.Taking the MM32F0160 series MCU from Nuvoton as an example, this series of MCUs features a FlexCAN module that adheres to the ISO 11898-1 standard, CAN FD, and CAN 2.0B protocol specifications. It is not only compatible with traditional CAN but also supports the CAN FD mode. In the CAN FD mode, it can achieve a communication rate of up to 8 Mbps in FD mode, supports both standard frames (with 11-bit identifiers) and extended frames (with 29-bit identifiers), supports a maximum payload of 64 bytes, and has a very flexible mailbox system for transmission and reception.

For instance, the MCU/MPU products from New Tang Dynasty with CAN FD interfaces, such as M253, M463, and M467, can support up to 4 interfaces. Among them, the M467 chip communicates with multiple battery packs through 4 CAN FD interfaces to obtain battery pack data. This application requires a stable transmission rate of over 5 Mbps and uses New Tang's unique HyperBus to connect with HyperRam for temporary data storage. Compared to SRAM, HyperRam offers lower power consumption and cost. Subsequently, the data is transmitted to the monitoring end for processing via an Ethernet port.

To enhance the usability of their products, processor manufacturers also provide development boards through independent research and development or collaborative efforts. For example, the MD9360 core board is equipped with the Xinchi D9-Pro six-core Cortex-A55 processor, with a clock speed of up to 1.6GHz, supporting 16 serial ports, 4 CAN FD interfaces, and 2 gigabit Ethernet ports. This core board can be used in industrial fields such as motion control, construction machinery, and display terminals.

The aforementioned CAN FD transmission and reception, the related solutions are also very rich. For example, Texas Instruments' TCAN3413 and TCAN3414 are Controller Area Network (CAN) FD transceivers that meet the physical layer requirements of the high-speed CAN specification ISO 11898-2:2016. These transceivers have certified electromagnetic compatibility (EMC) and are suitable for traditional CAN and CAN FD networks with data speeds up to 5 megabits per second (Mbps). These devices can achieve operation speeds of up to 8 Mbps in simpler networks. The main application scenarios for Texas Instruments' TCAN3413 and TCAN3414 include factory automation, power grid infrastructure, industrial transportation, and motor drivers.

In conclusion, in complex industrial automation systems that require high-speed data exchange, such as high-speed robot control and real-time monitoring systems, the demand for CAN FD is still strong. It fills the gap between traditional CAN and Ethernet, and the product types of industrial-grade CAN FD, whether it be MCUs, transceivers, or converters, are currently very diverse.