My ATmega128RFA1 has both AVSS and DVSS. I've just finished reading this to explain the difference:
So are AVSS and DVSS connected internally within the AVR? (I'm guessing no)
Which one should I use as my ground plane? (I'm guessing AVSS)
"And if you connect the analogue and digital grounds together do it only in one single well-designed place."
What happens if I don't connect them at all? What would make it 'well-designed'?
And in the Application Circuit, why are the crystals attached to Analog ground?