The four buttons and four LEDs on the nRF21540 DK are connected to dedicated General-Purpose Input/Output (GPIO)s on the nRF52840 System on Chip (SoC).
| Part | GPIO | GPIO alternative | Solder bridge |
|---|---|---|---|
| Button 1 | P0.11 | P1.07 | - |
| Button 2 | P0.12 | P1.08 | - |
| Button 3 | P0.24 | - | |
| Button 4 | P0.25 | - | |
| LED 1 | P0.13 | SB5 | |
| LED 2 | P0.14 | SB6 | |
| LED 3 | P0.15 | SB7 | |
| LED 4 | P0.16 | SB8 |
If P0.13–P0.16 are needed for other functions, the LEDs can be disconnected by cutting the short on SB5–SB8 (see Disconnecting the LEDs). Since P0.11 and P0.12 are used as a part of the trace functionality, Button 1 and Button 2 can be moved to alternative GPIOs (see Debug input and trace) .
The buttons are active low, meaning that the input is connected to ground when the button is activated. The buttons have no external pull-up resistor. To use the buttons, P0.11, P0.12, P0.24, P0.25 pins must be configured as an input with an internal pull-up resistor.
The LEDs are active low, meaning that writing a logical zero (0) to the output pin illuminates the LED.
