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TCAN1043-Q1: How to wake up a sleeping device

Michael Lamb
Prodigy 40 points
Part Number: TCAN1043-Q1
Other Parts Discussed in Thread: TCAN1043

(Sorry if this is a basic question. I'm pretty new to CAN and this might be a more general CAN question, but I can't find the answer.)

We are using a TCAN1043 and I need to design a test for the wake-on-CAN feature. INH is routed to the power controller so that when INH signals, power will wake the entire device.

What I don't know how to do is wake the sleeping chip up from the CAN bus. As I understand it, I need to place a wake up pattern on the CAN bus. This must be from some external source since our hardware is sleeping. How do I do that?

Is there some test hardware or software that can do this? What does TI use to wake a sleeping device? What's the simplest maybe?

Thanks in advance for any help.

  • 0
    TI__Guru 62920 points
    Hi Michael,

    You're right that a wake-up pattern (dominant/recessive/dominant) can be used on the CAN bus to wake up all the nodes that connect to it. When everything is asleep, though, it can be difficult to generate this pattern. This is why there is also a mechanism for a "local" wake-up of a CAN node via the WAKE line. This is a high-voltage input that is referenced to the battery rail, and any change of state on it will be detected by the transceiver and used to initiate a wake-up (i.e., INH drives high). In applications that need to wake up before the CAN bus is active, it is common to control the WAKE line via a push button/switch/high-voltage IO/etc.

    Please let me know if this doesn't make sense or if you have any other questions.

    Regards,
    Max
  • 0 in reply to Miguel Robertson
    Prodigy 40 points
    Thanks for the response. This was my first suggestion to the electronic design folks but they have WAKE grounded. We could enable it for test hardware but the production hardware will still have WAKE disabled and we will need to test that too.

    There must be some relatively simple way to create the pattern - some CAN adapter or evaluation board with some code or even some LabView code or something similar. Is TI able to share what they used to test it?

    Thanks.
  • 0 in reply to Michael Lamb
    TI__Guru 62920 points
    Michael,

    A simple set-up would be to get a CAN transceiver evaluation board, power it up, connect the CANH/CANL lines to your system, and then drive the wake-up pattern on the TXD input to the transceiver using a function generator. Here's an example of a board that could be used:

    www.ti.com/.../TCAN1042DEVM

    Also note that the wake-up pattern would be present in any CAN bus activity that uses an arbitration rate of 500 kbps or less (i.e., a large majority of CAN implementations). So, if you had any test equipment that could generate CAN bus traffic at this rate (Vector's CANalyzer would be one example) you could simply connect it to your system via the CAN port.

    Do you have access to anything that communicates via CAN and would be active at power-on without requiring a wake-up?

    Regards,
    Max
  • 0 in reply to Miguel Robertson
    Prodigy 40 points
    Thank you. I think that's the information I am missing. (Again, I am new at this.) We have plenty of test equipment and CAN devices capable of transmitting.

    So to reiterate, we would just need to send a bit of normal CAN traffic on to the connected bus and as long as the speed is 500K or less INH should go high which.
  • 0 in reply to Michael Lamb
    TI__Guru 62920 points
    Michael,

    Yes, that's right. This is because to wake up this device requires reception of a dominant period followed by a recessive period followed by another dominant period, each of which exceeds the tWK_FILTER duration. The maximum filter duration of this particular transceiver is 1.8 us, and at 500 kbps then each bit is 2 us long. So, all it takes to wake up is a single dominant bit, then a single recessive bit, then a single dominant bit. This sequence will always occur during the overhead of a CAN frame, so any traffic at 500 kbps or less will qualify.

    Max