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CC1312R: 32.768 kHz oscillator

ppielorz
Prodigy 190 points
Part Number: CC1312R

Dear all,

I've searched through documentation and E2E forum for the clear answer of my question: is a low frequency crystal really needed?

I read "CC13xx/CC26xx hardware configuration and PCB design considerations" document and in chapter 3.1.2 there is a statement:

"An external crystal is required for timesynchronous protocols such as TI 15.4-Stack and wM-Bus."

However in many threads people asked about this oscillator and nowhere this information was confirmed. I tried myself by setting SET_CCFG_MODE_CONF_SCLK_LF_OPTION to 0 and the sensor example application worked without problem.

I'm working on application with very tight space constraints so I would be glad if I could skip this oscillator. I want to use it with TI 15.4 Stack and achieve the lowest possible energy consumption.

Regards,

Pawel

  • 0
    TI__Guru**** 317180 points

    As far as I could find out last time I checked is that the 15.4 stack is not tested without a 32 kHz xtal. My understanding is the the timing is not very tight in the stack allowing some inaccuracy in the clocks. 

    It's possible to apply the 32 kHz on a pin. For testing you can set this +/- a number of ppm and see when the system fails using a launchpad. Then if the allowed inaccuracy is larger than the expected RCOSC inaccuracy you should be fine. I believe it would also depend if you are using frequency hopping or not since the hopping require a stable time source.