The firmware development mode is active with the nRF ONLY switch (SW6) in the DEFAULT position.
The nRF only mode disconnects the power supply and LEDs of the interface MCU. It also disconnects the signal lines between the nRF52833 System on Chip (SoC) and the interface MCU using analog switches.
This is done to isolate the chip on the Development Kit (DK) as much as possible, and can be of use when measuring currents on low-power applications.
Figure 1. nRF ONLY switch (SW6)
