The exact clamping voltage isn’t specified in the public datasheet, as it depends on process variation. Typically, the internal ESD diodes start conducting around 0.3 V below GND and 0.3 V above VCCIO. When clamping diodes are disabled, external protection (like TVS diodes) should keep the I/O voltage within that same range to prevent damage. For precise limits, refer to the “Absolute Maximum Ratings” section in the Cyclone V Device Datasheet.
