In the Treatment of Unused Pins section of the user's manual: hardware, it states that "These pins can be left while PORTn.ICR is in the initial state (the input buffer disabled)*". Is it correct to understand that unused ports on hardware (in an unconnected, open state) are also acceptable? When using the above, is either input or output acceptable?
Yes, provided that the ports in question are not read. The pins may be in either input or output state. Note that pin handling is necessary if you wish to read a port.