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TCAN1044V: Nominal Bit Rate v.s. Data Bit Rate

Roy Hsu
Genius 9360 points
Part Number: TCAN1044V


Hi Team,

My customer brought to me a question about the distinction between Nominal Bit Rate and Data Bit Rate. Do you know the differences between these 2 terms?

When referring to a competition device, it seems that Nominal Bit Rate represents the "Arbitration Bit Rate". Do we also have a similar spec to that?

Thanks!

Roy

  • 0
    TI__Guru 53575 points

    Hi Roy,

    CAN FD allows a different data rate to be used during the arbitration phase and data phase of each CAN frame. During the arbitration phase, multiple nodes may be transmitting on the bus simultaneously. During this phase, there are several factors that limit the maximum achievable data rate of the system, so this is generally around 500kbps max. During the data phase, only one device is transmitting on the bus so a higher data rate may be used. This is where we get FD rates up to 2Mbps or 5Mbps. 

    Because the CAN transceiver itself is only concerned with the physical layer of the ISO 11898-2 spec, it doesn't care which phase the CAN frame is in. From this perspective, only the highest data rate used in the system needs to be supported by the transceiver. For example, the TCAN1044V supports up to 8Mbps speeds, so this would be suitable for a system who's max rate is 5Mbps in the data phase and 500kbps in the arbitration phase. As long as neither of these rates exceed the transceivers maximum, it will be suitable for those system speeds. 

    Let me know if you have any more questions.

    Regards,
    Eric Schott