Using external clock signal for LFCLK

[Chris]

Dear All,

for the next revision of our product we've added a RTC / calendar IC with 32kHz clock output and it would be great if I could save some real estate by using the clock output for the nRF52840 LFCLK to be able to eliminate the currently populated crystal including caps.

The docs say - as far as I understand correctly - to connect the CLKOUT to P0.00/XL1 and XL2 to ground, right? I'm asking because the chip in use (RV-8263-C7) requires a "clock enable" signal and I'm wondering if I could use XL2/P0.01 to enable the clock only when required.

Any advise?

Thanks,

Chris

[haakonsh]

You can't use XL2/P0.01 as a GPIO when you use an external crystal/clock signal. 

You also need to set the BYPASS and EXTERNAL bits in LFCLKSRC: 

NRF_CLOCK->LFCLKSRC |= (1 << 16) | (1 << 17);

[Chris]

Thank you @haakonsh