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DEEP SLEEP modes on the AM1808

Nathan Zuber
Prodigy 90 points
Other Parts Discussed in Thread: AM1808

I want to use the deep sleep function on the AM1808.  I want it to be woken up by either of two events, 1) RTC or 2) external signal.  I have found how to implement each of them individually, but in order to implement the RTC, you must set the RTC_ALARM pin (which is also the deep sleep pin) to an output.  Then when the RTC_ALARM pin is driven by the RTC high, it also drives the \DEEP_SLEEP pin high and brings the chip out of deep sleep.

Is it possible that we may still be able to drive the \DEEP SLEEP pin high externally, even if it has been configured as an output for RTC triggering? 

  • 0
    TI__Guru* 83935 points

    Hi Nathan

    Nathan Zuber said:
    Is it possible that we may still be able to drive the \DEEP SLEEP pin high externally, even if it has been configured as an output for RTC triggering? 

    Unfortunately no. You can either use RTC_ALARM for entry and exit from Deep Sleep mode or you can use the DEEP SLEEPz pin (controlled externally) to enter and exit deep sleep mode. As you noted, the pin has to be configured as output in case you want to exit deep sleep mode via RTC_ALARM wake up and as an input to be woken up via DEEP SLEEPz pin control, these are mutually exclusive functionality.

    Regards

    Mukul

     

  • 0 in reply to Mukul Bhatnagar
    Prodigy 90 points

    Is there a recommended way around this?  An external timer or something else I am not considering?

  • 0 in reply to Nathan Zuber
    TI__Guru* 83935 points

    Hi Nathan

    Unfortunately ,not a way that allows you to make use of the integrated RTC on the device. Since in deep sleep mode , the entire device is in "clock freeze" state, there is no device state machine that can send a wake up event apart from either the DEEPSLEEz pin toggle or RTC_ALARM event.

    One possible solution , if you need both an RTC alarm based wake up as well as DEEPSLEEPz based wake up, could be to use an off the shelf RTC , this could be a cost adder, but then you could possibly have an RTC ALARM signal from the off chip RTC and DEEPSLEEPz  control signal, with some glue logic, allow entering/exiting the Deep Sleep mode, using the entering/exiting deep sleep mode via externally controlled wake up sequence documented in the System Guide.

    While I know at first blush the mutual exclusiveness of DEEPSLEEP pin vs RTC_ALARM event wake up will appear to be a design quirk, but being close to the design/arch phase of the device, I can tell you that we added Deep Sleep mode pretty late in to the development (it doesn't even exist in some of the other devices in the same family e.g. OMAPL137 or c6747 etc), and initially it was only going allow wake up through the DEEPSLEEP pin toggle --> enabling wake up through RTC_ALARM event was almost additional creativity on the chip specification owner's part to get "more" out of the existing deepsleep feature set.

    Hope this helps.Let us know if you have more questions.

    Regards

    Mukul