19.14.1 Single-Ended Conversion

For single-ended conversion, the result is as follows

ADC = V IN ⋅ 1024 V R E F

where VIN is the voltage on the selected input pin, and VREF the selected voltage reference (see also descriptions of ADMUX.MUX). 0x00 represents analog ground, and 0x3FF represents the selected reference voltage minus one LSB. The result is presented in one-sided form, from 0x3FF to 0x000.

Note: When ADCL is read, the ADC Data Register is not updated until ADCH is read. Consequently, if the result is left adjusted and no more than 8-bit precision is required, it is sufficient to read ADCH. Otherwise, ADCL must be read first, then ADCH.