Datasheet

RST - this is the Reset pin, tie to ground to manually reset the AVR, as well as launch the bootloader manually

ARef - the analog reference pin. Normally the reference voltage is the same as the chip logic voltage (3.3V) but if

you need an alternative analog reference, connect it to this pin and select the external AREF in your firmware.

Can't go higher than 3.3V!

Debug Interface

SWCLK & SWDIO - These pads on the bottom are used to program the chip. They can also be connected to an

SWD debugger.

https://learn.adafruit.com/adafruit-feather-m0-express-designed-for-circuit-python-

circuitpython

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