AVR-Chat

> The ATMega16's datasheet shows that the I/O pins have diodes from the pin to
> Gnd and Vcc.  These would seem to protect the pin from surge voltages less
> than Gnd or greater than Vcc but I do not see any specification as to what
> the max current capability of these diodes is.
>

They do tell you not to put any current through the protection diodes.
From a practical POV, I'd want to stay in the low microamp range..