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AR# 19808

Spartan-3/-3E - What happens to unused I/O pins after configuration?


What happens to the unused I/O pins on Spartan-3/-3E devices after configuration?


By default, unused I/O pins exhibit high impedance with an internal pull-down enabled. The value of the pull-down depends on VCCO. The pull-down range is denoted by the IRPD parameter in the Spartan-3/-3E Data Sheet.

The Spartan-3 DC and Swtiching Characteristic Data Sheet is located at:


The Spartan-3E DC and Swtiching Characteristic Data Sheet is located at:


You can use the following BitGen option to set the state of unused I/O:

bitgen -g Unusedpin:Pullup

For a list of BitGen options available for Spartan devices, enter the following:

bitgen -h spartan3


bitgen -h spartan3e


- The first value listed is the default value. For example, "Pulldown" is the default value of "UnusedPin option: UnusedPin Pulldown, Pullup, Pullnone."

- Replace "spartan3" with appropriate device architecture if necessary.

- You can also specify the Unused IOB Pins value in the Generate Programming File Properties -> Configuration Options inside of Project Navigator.

AR# 19808
Date Created 09/03/2007
Last Updated 02/27/2013
Status Active
Type General Article