3 Replies Latest reply on May 20, 2015 1:28 PM by MichaelF_56

    32kHz Crystal Spec?

      What is the spec for the 32kHz xtal used with the BCM20737?


      Or alternately, please provide the manufacturer & part number of a 32kHz crystal known to work.




        • 1. Re: 32kHz Crystal Spec?


          Hope this helps....

          • 2. Re: 32kHz Crystal Spec?



            Do you have a TAG3 board handy?  Note that you should be able to use it and the sample rtc_sample app from the SDK to get the external xtal working on the dev board (SoC based). The The specified item was not found. guide walks you through which resistors to populate in order to get this working.


            * RTC Sample


            * This application provides the sample code for interfacing with

            * the on-chip RTC clock. It is highly recommended that an external 32K

            * xtal be used when accurate time is to be maintained. The accuracy

            * of the time maintained with the an external LPO is an order of magnitude

            * better than the internal LPO.



            * Features demonstrated

            *  - Use of the on-chip RTC interface.

            *  - Use of the external 32 KHz LPO for sleep and deep sleep.

            *  - Entering deep sleep on demand.

            *  - Using the external LPO (32KHz xtal) for timed wake from deep sleep.


            * To demonstrate the app, work through the following steps.

            * 0. Enable the external 32KHz oscillator on the TAG board (see Quick Start Guide -

            *    make sure that R102 and R103 on BCM920737TAG_Q32 are populated

            *    with a 0 Ohm resistor, else the the behavior is undefined).

            * 1. Plug the WICED eval board into your computer

            * 2. Build and download the application (to the WICED board)

            * 3. Application initializes and RTC and prints time every second.

            * 3.a Application programs and enters deepsleep, optionally configuring for a timed wake.



            The 32.768KHz crystal is shown on the TAG3 schematic in the Hardware User Guide (SDK 2.x and TAG3 Board), but I could not find a part number for the device within the TAG3 Development Board Bill of Materials


            In addition, jota_1939431 also got a similar setup working on the SIP module as well as a result of the debugging that took place in this thread: Re: rtc_sample bricks our BCM20736S-based board


            I will ask him to respond to this thread with a part number as he is involved in building a new TAG board to replace this one and should have the part number handy.

            • 3. Re: 32kHz Crystal Spec?

              Closing per the dialog created outside the forum for the same request.