4.4.2 User LED
There is one yellow LED, D200, available for use by the application SW. The LED is lit when PB5 is set to a high state.
The LED is connected to ATmega328PB pin 17 - PB5, as shown below.
Info: PB5 is the clock signal of the SPI bus and is also
connected to the mEDBG for programming. The mEDBG tri-states its I/O when the
programming interface is not in use.