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 nRF52840 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)s on the connectors.
Note: When using ANT™/ANT+™,
the 32.768 kHz crystal X2 is required for correct operation.
If
P0.00 and P0.01 are needed as normal I/Os, the 32.768
kHz crystal can be disconnected and the GPIO can be routed to the connectors. Cut the solder
bridges on SB1 and SB2 and solder SB3 and SB4. See
the following figures for details.Figure 1. Configuring P0.00 and P0.01
Figure 2. 32.768 kHz crystal and SB1–SB4