OR ... does differential just mean the difference in voltage between a pair of ADC pins - to save you having to take two ADC readinsg and subtract the results?
This is the case, the chip's I/O pins electrical safety limits always applies, no voltage higher the +Vcc and no negative voltages. Only the reset pin allows for voltage above +Vcc as a means to enter high voltage programming mode where +12vdc is used on the reset pin.