analogReadResolution() is an extension of the Analog API for the Arduino Due, Arduino and Genuino Zero and MKR1000.
Sets the size (in bits) of the value returned by analogRead(). It defaults to 10 bits (returns values between 0-1023) for backward compatibility with AVR based boards.
The Due, Zero and MKR Family boards have 12-bit ADC capabilities that can be accessed by changing the resolution to 12. This will return values from analogRead() between 0 and 4095.
bits: determines the resolution (in bits) of the value returned by analogRead() function. You can set this 1 and 32. You can set resolutions higher than 12 but values returned by analogRead() will suffer approximation. See the note below for details.
If you set the analogReadResolution() value to a value higher than your board's capabilities, the Arduino will only report back at its highest resolution padding the extra bits with zeros.
For example: using the Due or the Zero with analogReadResolution(16) will give you an approximated 16-bit number with the first 12 bits containing the real ADC reading and the last 4 bits padded with zeros.
If you set the analogReadResolution() value to a value lower than your board's capabilities, the extra least significant bits read from the ADC will be discarded.
Using a 16 bit resolution (or any resolution higher than actual hardware capabilities) allows you to write sketches that automatically handle devices with a higher resolution ADC when these become available on future boards without changing a line of code.
Corrections, suggestions, and new documentation should be posted to the Forum.
The text of the Arduino reference is licensed under a Creative Commons Attribution-ShareAlike 3.0 License. Code samples in the reference are released into the public domain.