1 Reply Latest reply on Mar 18, 2014 5:36 AM by ShawnA_01

    How can I get '20732S to use 32K Crystal for low power mode?


      In my application design I am using a 20732S and have attached a 32khz crystal.

      However I don't think the chip is using the crystal. 

      Is there anything I need to do to enable this function?


      My goal in using the crystal is to use less energy when the chip is in a low power state. 


      Specifically, I would like to have the chip be asleep with the radio off, while still running a free running counter to support the real time clock API, and have the chip wake up on an interrupt from an accelerometer.


      Is this possible?  How do I cause the chip to shut down the radio and enter a low power state?

        • 1. Re: How can I get '20732S to use 32K Crystal for low power mode?

          The official software and documentation change is in progress for designs choosing to use the optional crystal, instead of the Low Power Oscillator (LPO).  For software, the strategy will be to provide an API that applications can call to enable the crystal circuit and re-mux the pins that are shared with those pins.


          Note: Due to internal pin multiplexing and packaging decisions, the use of the optional crystal affects some of the alternate pin functionality.


          For BCM20732S (48-pin LGA) module designs, the crystal consumes:

          · Pin 43 (XTALO32K) which makes ADC/GPIO:P12 unavailable.  P26 may still be available.

          · Pin 44 (XTALI32K) which makes ADC/GPIO:P11 unavailable.   P27 may still be available.


          Internal conversations are taking place for final documentation, but it looks like customers using the BCM20732S device may also be able to continue to use P26 and P27; which is contrary to the currently published Technical Reference Manual.  Standby for final disclosure...