Honored ContributorCould 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"
Honored ContributorTo 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.Honored ContributorHonored ContributorTechnically 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.
