nRF52832 XTAL on single pin

[aff]

Hello,

I'm trying to connect external RTC, which has a 32kHz clock on it's pin to nRF52832. So far I've had issues with connecting this clock to P0.00 pin and having P0.01 be a gpio. Is this configuration possible (XTAL on single pin) or am I just unable to get it to work? 

[bjorn-spockeli]

Hi Aff,

in order to use a single-ended LFCLK source to the nRF52832 you need to do the following:

• The external clock signal must be connected to XL1 pin,
• XL2 pin may be left floating or be grounded (if the signal voltage isn't rail-to-rail),
• LFCLK MUST be configured for external clock signal and started BEFORE enabling the SoftDevice,
• The Softdevice may now be initialized with NRF_CLOCK_LF_SRC_XTAL for the LFCLK.

See the following DevZone posts for more information

https://devzone.nordicsemi.com/f/nordic-q-a/29771/nrf52832-external-xl-lf-clock
https://devzone.nordicsemi.com/f/nordic-q-a/15284/nrf52832-lfclk-external-signal-and-soft-device/58385#58385

Best regards

Bjørn 

[aff]

Thanks for the quick response!

I saw those threads and they were really helpful but there were no threads about using the spare pin as gpio. The datasheet says it may be left floating or grounded in rail-to-rail clock scenarios, but nothing is mentioned about using the gpio functionality so the main concern is whether XL2 can be a gpio while XL1 is used as clock-in. The assumption is no, but i figured i'd ask to be sure. The main question of the thread might not have been worded properly, sorry!

[bjorn-spockeli]

My understanding is that the pin should be floating or grounded(depending on the ext. clock source), i.e. it cannot be used as a GPIO. 

-Bjørn