1. CAN Protocol Evolution: From CAN to CAN FD

CAN FD (Flexible Data Rate) is an abbreviation for "Variable Data Rate CAN," which can be understood as a protocol layer upgrade of the traditional CAN bus. It's important to note that CAN FD only upgrades the communication protocol; the physical layer remains unchanged. This design aims to address some bottlenecks of traditional CAN while ensuring compatibility.

As automotive electronic systems become increasingly complex and data interaction becomes more frequent, the traditional CAN 2.0 bus faces severe load issues, with load rates reaching as high as 95% in some scenarios. Meanwhile, the CAN bus also suffers from the following major limitations:

* Maximum transmission rate limited to 1 Mbit/s (the actual common rate is 500 kbit/s);

* Excessive frame overhead; in traditional CAN, less than 50% of the bandwidth in a frame is used for effective data transmission;

* Frame data segments are only 8 bytes, making it difficult to meet the demands of modern applications for large-volume communication;

* Latency is limited by the physical architecture, such as ACK response delay, transceiver and wiring propagation delay, etc.

In comparison, other communication protocols have significantly lower overhead. For example:

* UDP: Only 64 bytes of a 1500-byte data packet are overhead;

* FlexRay: Only 8 bytes of a 254-byte data packet are control overhead.

Since the automotive industry cannot completely abandon the existing CAN architecture and redesign, CAN FD was developed to ensure compatibility with existing systems, control upgrade costs, and improve bus performance. CAN FD development began in 2011 and was officially incorporated into the ISO 11898-1 standard in 2015, coexisting with the classic CAN protocol.

CAN FD has two core improvements over traditional CAN:

1. The data segment length is extended to 64 bytes;

2. Higher transmission rates (maximum 8 Mbit/s) are supported in the data phase.

These improvements significantly increase communication efficiency, reduce bus load, and make it more suitable for today's demands for high-speed, high-capacity data transmission. Therefore, CAN FD is not only a continuation of traditional CAN but also an important evolution for future in-vehicle networks.

As shown in the diagram, the overall structure of the CAN FD frame follows the basic framework of the classic CAN frame, but significant expansions have been made to the control and data fields to support higher bandwidth and larger data transmission volumes. The Start of Frame (OF) bit identifies the beginning of a data frame, similar to traditional CAN. The subsequent arbitration field contains an 11-bit identifier and a reserved bit (r1) for bus arbitration and frame priority determination. The control field is a key extension area of CAN FD. In addition to retaining the IDE bit, the newly added EDL (Extended Data Length) bit clearly distinguishes CAN FD from traditional CAN messages. The introduction of the BRS (Bit Rate Switch) bit allows the data segment and CRC field to switch to a higher transmission rate after the arbitration phase. The ESI (Error State Indicator) bit is used to characterize the error state of the transmitting node, thus assisting the system in fault tolerance assessment. The data segment is the core of CAN FD's bandwidth enhancement. Its length can be specified by the DLC field, extending from a maximum of 8 bytes in traditional CAN to a maximum of 64 bytes, significantly increasing the payload per frame. Consequently, the CRC checksum field is also enhanced, using either a 17-bit or 21-bit CRC depending on the data length, improving data integrity. The ACK, EOF, and IFS at the end of the frame remain consistent with traditional CAN, ensuring good backward compatibility for CAN FD.

3. Differences between Standard CAN FD and Bosch CAN FD

CAN FD was first proposed by Bosch, called Bosch CAN FD. As an extension of the traditional CAN bus, it mainly introduces a larger data length (up to 64 bytes) and a higher data segment rate (up to 8 Mbps). Its frame structure uses a 17-bit CRC checksum and does not require bit time resynchronization. However, with the increase in communication speed and load in practical applications, the Bosch version had certain limitations in data reliability. Therefore, in 2015, the ISO organization released the formal standard ISO 11898-1:2015, which is now known as the standard CAN FD. While retaining the main features of the Bosch version, it introduced a stronger 21-bit CRC check mechanism and fine-tuned the frame format, enhancing its anti-interference capabilities. The two are physically layer compatible, but differ in frame structure, check algorithm, and protocol fault tolerance mechanisms. Therefore, the standard CAN FD node is more versatile and reliable, while the Bosch version, being an earlier experimental version, has been gradually replaced by the ISO standard.

EID101-B111 Hub CANFD

Communication Interface: CAN

Operating Voltage: DC 8～28V

Product Dimensions: 100.1*17.6*112.3mm

Product Introduction: The EID101-B111 communication converter is a rail-mounted CANFD isolation repeater independently developed by Chengdu EBITE Electronics Technology Co., Ltd. This product uses a wide DC voltage range of 8V～28V, supports up to 5Mbps CANFD, is compatible with CAN 2.0, and has a built-in 120Ω matching resistor. The product is coated with a three-proof paint, providing anti-mildew, anti-moisture, and anti-salt spray functions.