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What about a High Speed CAN transceiver connected to Fault Tolerant Network?

UMBERTO BARONE
Prodigy 60 points

Hi All,

I am interested in understanding a practical approach in detecting a "wrong" CAN network setup based on the unexpected presence of one or more High speed CAN nodes (11898-2) connected to a Fault Tolerant Low Speed Network (11898-3).

Due to the different biasing and termination rules (the physical layer setup) I expect a wrong behavior of the network (EMC issues, Bus errors, etc) .

Do you have any indications/recommendations about solid evidences and test cases to apply for investigating a situation like that?

thanks in advance for the help,

  • 0
    TI__Guru 62910 points
    Hi Umberto,

    I would expect the high-speed nodes to report error frames when the low-speed/fault-tolerant nodes are transmitting and vice-versa, so this could give some level of detection. Beyond that, I'm not sure of a solution that would be able to narrow down the problem to a mismatch of physical layers. Since the two physical layers use different termination schemes, it may be possible for a node to detect the configuration of external resistors (e.g., by measuring recessive-level voltages or by measuring currents sourced by test voltage sources) and use that to deduce the network type.

    Max
  • 0 in reply to Max Robertson
    Prodigy 60 points

    Hi Max,

    I will try to implement some hw+fw diagnosis following your suggestions.

    I did few measurement just with oscilloscope and a CAN bridge. I found a significant change in the rising/falling edge on the H/L lines when the High speed transmit. 

    The resulting recessive states evolve like a compromise that move the steady voltage up-down according to overall impedance of each line. Beside the solution it was very interesting to observe.

    thanks a million for the reply.

    Umberto