Sharing 32.768kHz XTAL

[hasnaf]

If we are using an external RTC(for example, PCF85063) with a 32.768kHz XTAL, can we rely on the internal RC oscillator on nRF52840 for the power savings in Deep Sleep mode? If not, can we share the same 32.768kHz XTAL between RTC and nRF52840?

[ketiljo]

You can feed the 32 kHz signal from the RTX into the nRF52. See the LFCKSRC register. Also see table 1 here. 

Using the RC oscillator is also possible, but for long intervals, the crystal will be much more accurate.