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Question on CAN FD Vs Classic CAN

Poh Kok Keng
Genius 5512 points

hi,

 

I have a few questions on CAN FD protocol as follow: 

1)      What is the rate of transfer of CAN FD compare to CAN buses?

2)      Are there performance incompatibility when CAN FD and CAN modules be on the same backplane?

3)      Are CAN FD can be backward compatibility to CAN buses?

 

Rgds,

kpk

  • 0
    TI__Guru 62920 points
    Hi KPK,

    Classical CAN is limited to 1 Mbps. CAN FD allows for the data phase of a CAN frame to operate at a higher baud rate while the arbitration phase is still performed at classical CAN rates. The FD data phase's baud rate could theoretically extend up to 20 Mbps for CAN FD, but practical limitations (due to transceiver design, wiring used, EMC concerns, etc.) generally restrict this to around 5 Mbps (with a majority of applications operating at 2 Mbps).

    CAN FD is backwards compatible with classical CAN, but unfortunately classical CAN is not "forward compatible" with CAN FD; the FD frames will be seen as invalid by a classical CAN controller. For this reason, classical CAN and CAN FD modules cannot inter-operate over a shared network.

    Please let me know if you have any other questions. In case you are looking for a transceiver, the TCAN1042 family has variants (with "G" suffix) that are rated to operate up to 5 Mbps and meet all requirements of the ISO 11898-2 standard.

    Best regards,
    Max Robertson
  • 0 in reply to Miguel Robertson
    Genius 5512 points
    Hi Max,

    Thx for the reply. based on your explanation, if I have a system backplane are using Classic CAN network and I have a new device that running CAN FD network. Were this existing system work while adding a new CAN FD device? Or the other way around, there are CAN FD system network running in the backplane, I added an old device which is running a CAN network, Were this work together?

    it seems to me, it will only work in the situation where CAN FD is the receiver of the command but it cannot send back the command to classic CAN controller as it will treat as error frame. Is my interpretation correct?

    Rgds,
    kpk
  • 0 in reply to Poh Kok Keng
    TI__Guru 62920 points
    KPK,

    It sounds like your understanding is correct: if a classical CAN node receives and FD frame, it will indicate an error back to the bus. An FD node can receive classical CAN frames without issue, though. Since communication occurs in both directions (transmit and receive) on each node of a CAN bus, the classical CAN and CAN FD nodes would not be able to share a common network unless you could disable or silence the classical CAN nodes while FD traffic is present on the bus.

    Regards,
    Max