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AR# 14569

Synplify 7.1 - The global constraint "xc_fast_auto" overwrites HDL IOSTANDARD attribute settings

Description

General Description:

In Synplicity, when the global constraint "xc_fast_auto" is set, Synplicity writes the LVTTL IOSTANDARD attribute for all ports into the netlist. This constraint will overwrite any specific IOSTANDARD attribute that is assigned in the HDL.

Solution

The constraint "xc_fast_auto" controls the instantiation of fast output buffers in Virtex designs. Subsequently, the xc_fast_auto constraint can be overridden on an individual basis by the xc_padtype constraint.

For a brief description of these constraints, please see the Constraint Guide in the "Synplicity Constraints" section of the online software manuals:

http://toolbox.xilinx.com/docsan/xilinx5/data/docs/cgd/cgd0039_8.html

For a complete description of how to apply these constraints, please refer to the online help within the Synplify/Synplify Pro tool.

AR# 14569
Date Created 08/29/2007
Last Updated 12/15/2012
Status Active
Type General Article