# CAN FD

Protocols · `CAN FD` · verification: source checked

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.

## Specification

| Property | Value |
|---|---|
| Transports | other |
| Architecture | producer consumer |
| Encoding | binary |
| Standard body | ISO |
| Standard ref | ISO 11898-1:2024 |

## 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.

## 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.

## Sources

1. [CAN FD](https://www.can-cia.org/can-knowledge/can-fd-the-basic-idea) (accessed 2026-10-25)

---

Source page: https://machineschema.com/protocol/can-fd  
JSON: https://machineschema.com/protocol/can-fd.json  
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite Machine Schema and the original sources.