# Schmitt Trigger Input Hysteresis

GPIO and HSIO can be configured as a Schmitt Trigger input that, when enabled, exhibits a hysteresis that helps to filter out the noise at the receiver and prevents double-glitching caused by noisy input edges.

The following table lists the I/O standards that support the Schmitt Trigger feature. For more information about hysteresis values for different I/O standards when Schmitt Trigger mode is enabled, see respective PolarFire FPGA Datasheet or PolarFire SoC Advance Datasheet.

Table 1. Schmitt Trigger Control
I/O Standards Supported I/O Types Options
LVTTL

LVCMOS33

LVCMOS25

PCI

GPIO (input only) ON

OFF

LVCMOSI15

LVCMOSI18

HSIO (input only) ON

OFF

Schmitt Trigger mode is enabled by using the I/O attribute editor in Libero SoC or by using the following PDC command:

set_io -schmitt_trigger <value>

The value can be set as ON or OFF.