The nRF52840 System on Chip (SoC) can use an optional 32.768 kHz crystal X2 for higher accuracy and lower average power consumption.
On the nRF21540 DK, P0.00 and P0.01 are used for the 32.768 kHz crystal by default and are not available as General-Purpose Input/Output (GPIO) on the connectors.
Note: When using ANT™/ANT+™, the 32.768 kHz crystal
X2 is required for correct operation.