Four of the ADC bits in an AT90CAN128 are being used a digital outputs (they do not switch while any ADC conversion is in progress). The other four ADC bits are used for analog ADC inputs.
With a conventional analog ground plane covering all eight ADC pins (page 281 of the 7679C–CAN–01/07 data sheet), the four port F digital outputs would cross from the analog ground plane to the digital ground plane.
I'm thinking I could just run the digital ground plane all the way to the four digital pins and keep the analog ground plane isolated to the four analog pins, with a single common tie point between the digital and analog ground planes. I assume the internal port F uses a common internal ground (possibly referenced to pin 63?). The idea is to avoid potentially convoluted/noisy digital signal PC trace ground return paths through port F.
Does anyone have any recommendations on a good strategy for setting up mixed use PC board ground planes with some analog and some digital pins all on the same port like this?