The data sheet for the ATZB-S1-256-3-0-C states that the "Voltage on any Analog configured pin" must be less than 2.0V (absolute max).
However, from reading the ATMEGA256RFR2 data sheet (p. 553), it seems this limitation only applies to analog RADIO pins (specifically, pins 8,9,21,22,60,62).
Put another way: if I am using the on-board ADC, I can go up to Vcc (say 3.3V) without any harm to the device. Is that true?
Edit: never mind... I was misreading the section in the data sheet regarding the ADC. It looks like Vref is derived from AVDD, which is 1.8V....