Buongiorno. Io vorrei sapere a cosa servono i pin su arduino AREF e IOREF. AREF si trova sul gruppo dei pin (DIGITAL) e invece IOREF sul gruppo dei pin (POWER) di arduino uno. Grazie per eventuali risposte.
Sforzarsi e leggere il reference no ? 
IOREF :
IOREF. This pin on the Arduino board provides the voltage reference with which the microcontroller operates. A properly configured shield can read the IOREF pin voltage and select the appropriate power source or enable voltage translators on the outputs for working with the 5V or 3.3V.
AREF :
AREF. Reference voltage for the analog inputs. Used with analogReference().
... The Uno has 6 analog inputs, labeled A0 through A5, each of which provide 10 bits of resolution (i.e. 1024 different values). By default they measure from ground to 5 volts, though is it possible to change the upper end of their range using the AREF pin and the analogReference() function.
Guglielmo