We have detected your current browser version is not the latest one. Xilinx.com uses the latest web technologies to bring you the best online experience possible. Please upgrade to a Xilinx.com supported browser:Chrome, Firefox, Internet Explorer 11, Safari. Thank you!

AR# 2906

M1.4 CPLD - How to reserve a pin or a macrocell for future use?


Keywords: PROHIBIT, reserve pin, reserve macrocell

Urgency: standard

General Description:

The PROHIBIT constraint is not currently supported for CPLDs. In order to
reserve a pin(s) or a macrocell(s) redundant logic has to be used.


In order to keep the Fitter from using the pin or macrocell that you want to
reserve for future use, do the following:

Schematic Users -

Drive the pin that you want to reserve with a GND symbol. Make sure that there
is an OBUF between the GND symbol and the Output pad. Now put a LOC constraint
on this PAD, either in your schematic or using an UCF file. Compile your
design normally. In the 'Implemented Equations' section of the Fitter report,
you can see that the pin you wanted to reserve is now being driven by GND.

When you want to use this pin in future, just remove the GND symbol and connect
your logic to this pin.

The PROHIBIT constraint is available in version 1.5i software.
AR# 2906
Date Created 10/04/1997
Last Updated 03/29/2000
Status Archive
Type General Article