Clamping Diode logic option

A logic option that turns on the clamping diode of a pin.

This option is useful for limiting the overshoot voltage for a pin in an input operation. The clamping diode is turned on by default for the 3.0-V PCI and 3.0-V PCI-X I/O standards. The clamping diode is turned off by default for 3.3-V LVTTL and 3.3-V LVCMOS I/O standards.

This option is ignored if it is applied to anything other than a pin or a top-level design entity. This option is available for supported device (Arria^® II, Stratix^® III, and Stratix^® IV) families.