Bit Time Requirements for CAN FD

The new CAN FD frame format that is currently being integrated into ISO 11898-1 introduces a second bit time configuration into CAN networks. While the nominal CAN bit time is still used at the beginning and at the end of the frames, for arbitration and for acknowledge, called the Arbitration Phase; the new data bit time may be used for the main part of the frames, called the Data Phase. The data bit time may be shorter than the nominal bit time in order to speed up frame transmission. This paper describes the constraints for the CAN FD bit time configuration and how to harmonize the two bit rates for smooth switching between them. It also describes the transceiver delay compensation mechanism which is needed for data bit times that are in the range of or even shorter than the transceiver loop delay.