Preface
CAN is an efficient and reliable communication protocol designed for distributed real-time control systems. Its differential signal transmission and priority arbitration mechanism allow data to be transmitted stably in complex environments. The CAN protocol is not only the "behind-the-scenes hero" of the automotive industry, but also plays a key role in industrial automation, medical equipment and even aerospace! Its high reliability and real-time performance make complex systems simple and efficient. However, with the increasing use of CAN devices and the increasing number of bus devices, the maximum bus bandwidth of 1Mbps of traditional CAN can no longer meet the needs in some scenarios. In order to solve this problem, CANFD came into being in 2015, and CANFD is defined by the ISO-11898-1 standard.

Introduction to CAN

Origin: Launched by Bosch in Germany in 1986, it is mainly used to solve complex wiring harnesses and electromagnetic interference problems in automotive electronic systems.
Features:
Multi-master architecture: Any node can actively send data without a central controller.
Differential signal transmission: Transmitted through CAN_H and CAN_L twisted pair cables, with strong anti-interference ability.
Non-destructive arbitration: Bus conflicts are resolved through ID priority, and high-priority data is sent first.
High reliability: Built-in error detection, error recovery and fault isolation mechanisms.

CAN typical application scenarios

Automotive electronics: ECU (engine control unit), ABS, instrument panel, vehicle network (such as CAN-based diagnostic interface OBD-II).
Industrial control: PLC communication, robot control, sensor network.
Medical equipment: Internal communication of monitors and surgical equipment.
Aerospace: Airborne equipment communication.

Characteristics of CAN and CANFD

Standard frame

Extended Frame

Extension bit upgrade

Control bit upgrade
FDF bit identifies frame type (explicit = CAN, implicit = CANFD)
BRS bit triggers data segment rate switching (explicit = constant, implicit = accelerated)
ESI bit displays node error status (explicit = active error, implicit = passive error)
RRS bit ‌CAN FD cancels support for remote frames and instead uses the remote request replacement bit (RRS bit) to replace the traditional remote transmission request bit (RTR bit)

Summary

The CAN protocol was first introduced by Bosch to solve the complex wiring harness and electromagnetic interference in automotive electronic systems. Later, its application gradually expanded to industrial control, medical, aerospace and other fields. With the increase in application complexity and data volume, CANFD was introduced in 2015. CANFD has faster data transmission capabilities and more reliable verification, and CANFD is backward compatible with the CAN protocol, so it can be connected to ordinary CAN networks.