Use single output 32.768kHz TCXO as LFCLK source on nRF52840

[Matt M]

Hello,

I am working with a custom board that has the nRF52840 (via the ISP1807-LR-RS module). This board has the SIT1552AI-JE-DCC-32.768E MEMS TCXO. This TCXO chip has a single clock out line connected to pin P0.30 of the nRF52840. I see from the datasheet for nRF52840 that this is not one of the XL* lines. Is it still somehow possible to configure prj.conf and device tree to get the MCU to use this single-output TCXO as the 32.768 kHz clock source? I have tried looking for samples in the SDK that demonstrate this, but haven't found anything that looks to me like it pertains to my situation/setup (possibly I just completely missed or didn't recognize one that is actually there).

I am happy to answer questions and provide additional info as needed. Thanks for your help.

[RonaldHise]

Interesting project! You should be able to configure the nRF52840 to use the SIT1552AI-JE-DCC-32.768E on P0.30, even though it's not an XL* line. Check your device tree overlays for clock configurations; maybe you can reroute the low-frequency clock source like navigating a tricky Poptropica island! Dig into Zephyr's clock control subsystem docs – look for examples of external clock sources. Good luck!