Xilinx Constraints Guide

Chapter 4: Xilinx Constraints
VOLTAGE (Voltage)
The VOLTAGE (Voltage) constraint:
• Is a timing constraint.
Architecture Support
• Allows the specification of the operating voltage, which provides a means of
prorating delay characteristics based on the specified voltage.
Prorating is a scaling operation on existing speed file delays and is applied globally
to all delays.
Note Newer devices may not support VOLTAGE prorating until the timing information
(speed files) are marked as production status.
Each architecture has its own specific range of supported voltages. If the entered
voltage does not fall within the supported range, the constraint is ignored and an
architecture-specific default value is used instead. The error message for this condition
appears during static timing.
The following FPGA devices are supported for VOLTAGE:
• Spartan®-3A
• Spartan-3E
• Virtex®-4
• Virtex-5
Applicable Elements
Propagation Rules
Applies globally to the entire design.
It is illegal to attach this constraint to a net, signal, or design element.
Syntax Examples
The following examples show how to use this constraint with particular tools or
methods. If a tool or method is not listed, you cannot use this constraint with it.
UCF and NCF Syntax
VOLTAGE=value [V];
where
• value is a real number specifying the voltage
• V indicates volts, the default voltage unit
The following statement specifies that the analysis for everything relating to speed file
delays assumes an operating power of 5 volts.
VOLTAGE=5;
Constraints Editor Syntax
For information on setting constraints in Constraints Editor, including syntax, see the
Constraints Editor Help.
PCF Syntax
Same as UCF Syntax.
Constraints Guide
320 www.xilinx.com UG625 (v. 13.2) July 6, 2011