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ISO1044: B

Part Number: ISO1044
Other Parts Discussed in Thread: TEST,

For the Dominant time out measurement which faults are considered? Could it be MCU reset or Cable short?

  • Hi Satish,

    Thank you for posting, and welcome to E2E!

    ISO1044 features a driver-dominant time out (TXD DTO), which means the time-out circuitry is only triggered when the TXD input signal is LOW and the driver is keeping the bus in a dominant state, as shown in the test circuit and voltage waveforms below:

    This means if the CAN bus is shorted, the RXD signal will not timeout or change until the fault is cleared. If the MCU reset keeps the TXD pin LOW and the CAN bus dominant longer than ISO1044's tTXD_DTO spec of 1.2ms-3.8ms, then the driver-dominant time out will release the CAN bus.

    I hope this answered your question.

    Thank you,
    Manuel Chavez

  • What all test cases could result in dominant time out?

  • Hi Satish,

    Like Manuel pointed out earlier, TXD DTO is triggered only when TXD is held LOW for a time that is more than TXD_DTO spec (1.2 - 3.8ms) provided in the datasheet. This is the only way a TXD DTO is triggered.

    In a system, there can be many ways that could lead to above test situation and all these ways are entirely dependent on the system design and not dependent on ISO1044. A few examples include, MCU hardware fail that leads to making TXD LOW permanently, non-optimized MCU software that holds TXD LOW long enough to trigger DTO, MCU software stuck serving interrupts while holding TXD LOW causing DTO and system hardware failure leading to TXD pulled LOW permanently. These are just some examples that could be relevant or not to your system but there are many ways possible based on the overall system design. Since you know the system design well, you are the best person to find out different ways that could trigger DTO in your system.

    As for ISO1044, it only has one condition to trigger DTO like I mentioned above. Thanks.

    Koteshwar Rao