How much do you know about the CAN-FD protocol?

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How much do you know about the CAN-FD protocol? [Copy link]

       In the automotive field, as people's requirements for data transmission bandwidth increase, the traditional CAN bus is difficult to meet this increased demand due to bandwidth limitations. In addition, in order to narrow the bandwidth gap between the CAN network (max. 1MBit/s) and the FlexRay (max.10MBit/s) network, BOSCH launched CAN-FD. In this way, CAN-FD was born in this context.

ⅠWhat is CAN-FD? First, let's understand what CAN is? CAN: Controller area network, that is, controller area (local) network. CAN bus is one of the most widely used field buses in the world. It has become the standard bus for automotive computer control systems and embedded industrial control local area networks. CAN-FD: CAN with Flexible Data-Rate in English, translated as [CAN with variable rate]. On the basis of classic CAN, the transmission rate is increased, and the data field can transmit 64Byte, which is the function of variable speed. In simple terms, it is an upgraded version of CAN. CAN-FD inherits the main characteristics of the CAN bus, improves the network communication bandwidth of the CAN bus, improves the error frame leakage rate, and can keep most of the network system's software and hardware, especially the physical layer, unchanged. Ⅱ The main difference between CAN-FD and CAN CAN FD uses two ways to improve communication efficiency: one is to shorten the bit time and increase the bit rate; the other is to lengthen the data field length, reduce the number of messages and reduce the bus load rate. Three polynomials are used in the CRC check segment to ensure data reliability under high-speed communication. There are three main differences between CAN-FD and CAN: 1. The variable rate is variable from the BRS bit in the control field to before the ACK field (including the CRC delimiter), and the rest is the rate used by the original CAN bus. The two rates each have a set of bit time definition registers. In addition to using different bit time units TQ, the allocation ratio of each bit time segment can also be different. 2. Data field Payload length CAN FD has greatly expanded the length of the data field. DLC supports a maximum of 64 bytes. When DLC is less than or equal to 8, it is the same as the original CAN bus. When it is greater than 8, there is a nonlinear growth, and the maximum data field length can reach 64 bytes. 3. CRC check field In the process of CAN-FD protocol standardization, the reliability of communication has also been improved. Due to the different lengths of DLCs, when DLC is greater than 8 bytes, CAN FD selects two new BCH type CRC polynomials. III CAN-FD and CAN compatibility Although CAN-FD inherits most of the characteristics of traditional CAN, we still need to do a lot of work to upgrade from traditional CAN to CANFD. 1. Hardware We need to select CAN controllers and transceivers that support CAN-FD, and also select new network debugging and monitoring tools. 2. Network compatibility Pay special attention to the situation where some nodes of the traditional CAN network segment need to be upgraded to CANFD. Due to the inconsistency of frame formats, CANFD nodes can normally send and receive messages from traditional CAN nodes, but traditional CAN nodes cannot normally send and receive messages from CANFD nodes. The CAN FD protocol is the latest upgrade of the CAN-BUS protocol. It increases the 8-byte data per frame of CAN to 64 bytes, and the baud rate from the highest 1Mbps to 8-15Mbps, which increases the communication efficiency by more than 8 times, greatly improving the communication efficiency of vehicles. This technology has been monopolized by European and American companies until 2016, when Guangzhou Zhiyuan Electronics Co., Ltd., a leader in China's CAN-BUS, developed China's first CAN FD interface card based on the CAN FD IP core code with complete intellectual property rights, making China's bus technology level synchronized with the world's highest level.