digital ground AND analog ground?

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My ATmega128RFA1 has both AVSS and DVSS. I've just finished reading this to explain the difference:
http://www.epanorama.net/wwwboar...

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)

It says:
"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?

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A similar question was asked recently. Basically you don't want digital currents flowing through your analog ground as this will upset the analog performance. If you're using a prototype board, then join the grounds at a common point (star ground) or if you're designing a pcb, then have one ground plane but ensure that no stray currents flow through the analog side - put the power connector on the digital side, not the analog side.

Not connecting them would be a poorly designed circuit and probably would not work well.

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Whats confusing me though is that the application circuit in the datasheet shows a lot of digital stuff using the analog ground - the RF antenna (and supporting circuitry) and both crystals. Should I assume its a mistake in the documentation?

Also, the big center pad is for analog ground . . . would it be wise to connect digital ground directly to it, or somewhere else? I'm not really sure how these chips are internally wired, so its hard to guess where current will flow the most.

Otherwise, I think I understand it now.

How do YOU make a robot?
http://www.societyofrobots.com