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AR# 4100

3.1i XC9500 Family Hitop - PROHIBIT property does not exclude pins from "Programmable Ground Pins" option


Keywords: CPLD, Fitter, 9500, HITOP, PROHIBIT, property, programmable, ground

Urgency: Standard

General Description:
The PROHIBIT property can be used to reserve specific device pins so they remain
unused by the CPLD fitter. However, if you enable the implementation option
"Create Programmable Ground Pins on Unused I/O", all unused pins, including
those listed in the PROHIBIT property, are connected to the device's ground network.


This is fixed in the latest 3.1i service pack available at:

You can work around this problem without the service pack by creating dummy output
pins in your design instead of using the PROHIBIT property to reserve those pins.

A simple way to create a dummy output pin that remains at High-Z is to instantiate
a 3-state output buffer (like OBUFE) and tie the output enable pin (E) to ground.
In VHDL, you could use the following solution:

zero signal: bit :='0';
dummy_pin <= 'Z' when zero = '0' else '0';

AR# 4100
Date Created 06/23/1998
Last Updated 08/23/2002
Status Archive
Type General Article