Arduino Uno NC pin

Hardware
1

On the Arduino Uno, there's a pin to the left of IOREF. In the pinout diagram, it's labelled as NC. Does anyone know what does this pin do?
Arduino Uno pinout diagram

2

NC means "Not Connected"

However if you are talking abut the UNO-R4-WiFi it's actually connected to the BOOT pin on the processor.

On the R4-Minima it is connected to the BOOT pin and labelled as such.

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3

Thanks!

4

The original "UNO" style board form factor (which was actually established with its predecessor, the Diecimila) had several less pins. As new boards using this form factor but different microcontrollers were designed, it became clear that more pins were needed:

  • Dedicated I2C bus pins
  • A reference for the I/O voltage used by the microcontroller

These pins were added in a new "1.0 pinout" first used on the R3 revision of the UNO. It seems that the designers found the board could accommodate an additional pin, which was added in order to allow some expansion in the future without needing to make yet another pinout:

https://store.arduino.cc/products/arduino-uno-rev3/#:~:text=The%20second%20one%20is%20a%20not%20connected%20pin%2C%20that%20is%20reserved%20for%20future%20purposes.

Revision 3 of the board has the following new features:

  • 1.0 pinout: added SDA and SCL pins that are near to the AREF pin and two other new pins placed near to the RESET pin, the IOREF that allow the shields to adapt to the voltage provided from the board. In future, shields will be compatible with both the board that uses the AVR, which operates with 5V and with the Arduino Due that operates with 3.3V. The second one is a not connected pin, that is reserved for future purposes.
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