Xilinx Constraints Guide

Entering Multiple Constraints
File Name
Chapter 2: Entry Strategies for Xilinx Constraints
You can cascade multiple constraints for a given instance in the UCF file:
INST instanceName constraintName = constraintValue | constraintName = constraintValue;
For example:
INST myInst LOC = P53 | IOSTANDARD = LVPECL33 | SLEW = FAST;
By default, NGDBuild reads the constraints file that carries the same name as the input
design with a .ucf extension. However, you can specify a different constraints file name
with the -uc option when running NGDBuild. NGDBuild automatically reads in the
NCF file if it has the same base name as the input EDIF file and is in the same directory
as the EDIF file.
The implementation tools (for example, NGDBuild, MAP, and PAR) require file name
extensions in all lowercase (for example, .ucf) in command lines.
Instances and Blocks
The statements in the constraints file concern instances and blocks, which are defined
as follows.
• An instance is a symbol on the schematic.
• An instance name is the symbol name as it appears in the EDIF netlist.
• A block is a CLB or an IOB.
• Specify the block name with the BLKNM, HBLKNM, or XBLKNM attributes. By
default, the software assigns a block name on the basis of a signal name associated
with the block.
Constraints Guide
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