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TCAN1146-Q1: WUF flag in Normal Mode for Selective Wakeup

Omar Yousry
Prodigy 20 points
Part Number: TCAN1146-Q1

Hello,

I am currently working on a project using Can transceiver TCAN1146-Q1.

I need to ask about the Wakeup Flag (WUF) for selective wakeup. Isn't it set while being in the Normal mode?

As per datasheet, the WUF is detected and shown via CANINT flag in INT_1 register. However, when the transceiver is in normal mode, this bit is not set. 

AUTOSAR specs for Can transceivers states the following:

"For CAN transceivers supporting selective wakeup functionality, detection of wakeup frames is possible during Normal mode. Detected wakeup frames are signaled by the transceiver WUF flag. This ensures that no wakeup frame is lost during a transition to Standby mode"

Is there any other way to detect Wakeup frames (WUF) while being in normal mode? Is this supported?

Thanks.

  • 0
    TI__Guru 53555 points

    Hi Omar,

    Thanks for bringing your question to E2E. 

    Yes, wake up frame recognition is possible in normal mode when the SW_EN bit is set. However, this is not a typical use case for selective wake feature. Instead, the CAN controller should be responsible for monitoring CAN data when the transceiver is in normal mode and SW_EN should remain off. When it is time for the system to transition into a low power mode, the SW_EN bit can be set in the same SPI transaction that changes the transceiver mode (both of these bit fields are in the mode control register). This way if a WUF is received during the transition, the CAN controller will recognise the data on the RXD pin before the transceiver changes modes. If the WUF is received after the mode change, selective wake will be active and catch the frame because frame detection is active immediately after the mode change occurs. 

    Note that in the system, it is common to have the WUF repeat on the bus several times until the target node has responded to the wake request. This ensures that no wake request is missed due to mode transition time or when the transceiver does not have frame detection active yet due to an idle bus condition. 

    Let me know if you have any more questions. 

    Regards,
    Eric Schott