Datasheet

I2C pins on the nRF52840 require external pullup resistors to function, which are not present on the Adafruit

nRF52840 Feather by default. You will need to supply external pullups to use these. All Adafruit I2C breakouts have

appropriate pullups on them already, so this normally won't be an issue for you.

Logic pins

This is the general purpose I/O pin set for the microcontroller. All logic except for pin 5 is 3.3V output and input. You

can usually use 3V logic as an input to 5V,

but

the 3V Itsy pins should not be connected to 5V!

All pins can do PWM output - nRF52840 will assign a PWM to any pin you like

All pins can be interrupt inputs - nRF52840 will assign an IRQ to any pin you like

Special GPIO

Since you have PWM/IRQ on any pin, there's not a lot of special pins - they can all pretty much do anything, like

connect a PDM microphone or encoder. Here are the somewhat special pins:

#0 / RX - GPIO #0, also receive (input) pin for Serial1

#1 / TX - GPIO #1, also transmit (output) pin for Serial1

SDA and SCL - these are the I2C hardware interface pins. There's no pull up on this pin by default so when using

with I2C, you may need a 2.2K-10K pullup on each to 3.3V. PWM output

#3 - GPIO #3 is connected to the blue LED next to the Reset button - it isn't available on the pin breakouts

#4 - GPIO #4 is connected to the SW button to the right of the micro USB connector - it isn't available on the pin

breakouts

#5 - GPIO #5. This is a special OUTPUT-only pin that can PWM. It is level-shifted up to Vhi voltage, so it's perfect

for driving NeoPixels that want a ~5V logic level input. You can use this with our NeoPixel DMA control library to

automatically write NeoPixel data without needing any processor time (https://adafru.it/BkV).

SCK/MOSI/MISO - the hardware SPI port for connecting SPI devices, you can use any pin for CS

These pins are available in CircuitPython under the board module. Names that start with # are prefixed with D and

other names are as is. So #0 / RX above is available as board.D0 and board.RX for example.

QSPI Flash and DotStar

D2 and A1 thru A5 are 'low speed' pins, they can be used for < 10KHz signals but not recommended for

higher frequencies so as to avoid radio interference. Any other pins will work at high speeds!

