unused pins setting option in project settings

[Altera_Forum]

Could anybody point me to the documentation relating to the unused pins setting in the device and pin options of the project settings. My code started working when i changed the setting from the default "output driving ground" to "input tri-stated"

[Altera_Forum]

To my opinion, the options are self-explanatory. Setting unused pins to output has a danger to short some signals, that are connected to optional inputs but not yet defined as pins. Input with weak pull-up or hold is a safe option. 

 The purpose of setting unused pins as outputs is mainly in providing additonal ground pins to reduce ground bounce, partiularly with large PQFP packages.

[Altera_Forum]

--- Quote Start ---   The purpose of setting unused pins as outputs is mainly in providing additonal ground pins to reduce ground bounce, partiularly with large PQFP packages.  --- Quote End ---   How does it provide additonal ground pins?

[Altera_Forum]

Technically they aren't ground pins. But setting them as output driving ground connect them to the FPGA ground through a MOSFet. It is not as good as a real ground pin, but it can still help to decrease the total impedance (especially inductance) between the FPGA ground and the PCB ground plane, thus limiting the ground bounce.