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CAN FD

CAN FD is a CAN data link layer protocol that increases bit rate and payload size. It can transmit data faster than 1 Mbit/s and carries a data field of up to 64 bytes instead of 8 bytes. It uses the FDF bit to distinguish FD frames and the BRS bit to switch to the higher bit rate during the data phase.

Source checked3/3 values · 2026-10-25

Specification

1 source
Transportsother
Architectureproducer consumer
Encodingbinary
Standard bodyISO
Standard refISO 11898-1:2024

Study notes

  • Robert Bosch GmbH started CAN FD development in 2011 in cooperation with carmakers and other CAN experts.
  • CAN FD overcomes two CAN CC limits: data rates above 1 Mbit/s and a payload up to 64 bytes instead of 8 bytes.
  • A 1:8 ratio between arbitration-phase and data-phase bit rates gives approximately six times higher throughput, accounting for extra header and CRC bits.
  • The FDF bit distinguishes CAN FD data frames from CAN CC data or remote frames: recessive means CAN FD, dominant means CAN CC.
  • The BRS bit applies the second bit rate when recessive; when dominant, the arbitration-phase bit time setting is used in the data phase.
  • The ESI bit reports error status: dominant indicates error active, recessive indicates error passive.
  • CAN FD data frames with 11-bit identifiers use FD base frame format (FBFF); those with 29-bit identifiers use FD extended frame format (FEFF).
  • CAN FD does not support remotely requested data frames.
  • The CAN FD protocol controller also supports CAN CC frames.
  • CAN CC and CAN FD are standardized together in ISO 11898-1:2024.
  • The control field includes FDF, BRS, ESI and DLC bits in addition to CAN CC control bits.

Safety

  • The CRC field uses 17-bit polynomials for payloads up to 16 bytes and 21-bit polynomials for frames larger than 16 bytes, plus an 8-bit stuff-bit counter and a parity bit.
  • The document states these safeguards guarantee all single failures are detected under all conditions and improve multiple-failure detection.
  • Non-ISO CAN FD controllers are not compliant with ISO 11898-1 and do not implement the additional safeguard features.
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