RE: Sharing LF CLOCK with an SPI sensor

Mehmet — Thu, 31 Mar 2022 16:51:40 GMT

Thank you, Kenneth. I will take a look at the links now.

You are referring to a MEMS oscillator, right? (My sensor happens to be a MEMS accelerometer, that is why.

RE: Sharing LF CLOCK with an SPI sensor

Kenneth — Thu, 31 Mar 2022 13:56:30 GMT

Hello,

You may find these two tables useful:
https://infocenter.nordicsemi.com/topic/ps_nrf52840/clock.html#concept_xkj_np1_2r and
https://infocenter.nordicsemi.com/topic/ps_nrf52840/clock.html#unique_567737179

Note that the BLE softdevice may not have the api to configure BYPASS and EXTERNAL register, so you need to follow this description if you want to use external clock source:
https://devzone.nordicsemi.com/f/nordic-q-a/60702/enable-bypass-of-lfclk-crystal-oscillator-with-external-clock-source/247385#247385

But to answer your questions:

Unfortunately I think sharing a crystal driven by the nRF52840 will difficult since the amplitude will be around ~200mV, in addition the capacitance etc must be taken account for to ensure frequency accuracy. It's not possible to output a 32kHz from the nRF52840 in any low power way (it must be generated by the HFCLK in such case), so I think that is not an option either.

My suggestion if you want to share, then look into using a MEMS to supply 32kHz clock intput to XL1, just make sure to set BYPASS and EXTERNAL as in the devzone case linked above.

Best regards,
Kenneth