Xilinx Constraints Guide

Chapter 4: Xilinx Constraints
SCHMITT_TRIGGER (Schmitt Trigger)
Architecture Support
Applicable Elements
Propagation Rules
The SCHMITT_TRIGGER (Schmitt Trigger) constraint:
• Causes the attached input pad to be configured with Schmitt Trigger (hysteresis).
• Applies to any input pad in the design.
Applies to CoolRunner-II devices only.
All input pads and pad nets
This constraint is a net or signal constraint. Any attachment to a macro, entity, or
module is illegal.
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.
Schematic Syntax
• Attach to a net
• Attribute Name
SCHMITT_TRIGGER
• Attribute Values
TRUE
FALSE
VHDL Syntax
Declare the VHDL constraint as follows:
attribute SCHMITT_TRIGGER: string;
Specify the VHDL constraint as follows:
attribute SCHMITT_TRIGGER of signal_name : signal is “{TRUE|FALSE}”;
For more information about basic VHDL syntax, see VHDL Attributes.
Verilog Syntax
Place the Verilog constraint immediately before the module or instantiation.
Specify the Verilog constraint as follows:
(* SCHMITT_TRIGGER = “{TRUE|FALSE}” *)
For more information about basic Verilog syntax, see Verilog Attributes.
Constraints Guide
260 www.xilinx.com UG625 (v. 13.2) July 6, 2011