CAN FD controllers support classical CAN

CAN FD controllers can send and receive classical CAN frames as well as CAN FD frames. On the other hand, a classical CAN controller will always react with an error frame when receiving a CAN FD frame: A recessive bit in the position of the dominant r-bit in classical CAN is regarded as irregularity. The in classical CAN invalid value would be answered with an error frame. At this point it becomes transparent, that CAN FD frames will neither be understood, nor tolerated by traditional CAN controllers.