17.2.5 Digital Input Enable and Sleep Modes

As shown in the figure of General Digital I/O, the digital input signal can be clamped to ground at the input of the Schmitt Trigger. The signal denoted SLEEP in the figure, is set by the MCU sleep controller in Power-Down mode and Standby mode to avoid high power consumption if some input signals are left floating, or have an analog signal level close to V_CC/2.

SLEEP is overridden for port pins enabled as external interrupt pins. If the external interrupt request is not enabled, SLEEP is active for these pins. SLEEP is also overridden by various other alternate functions as described in Alternate Port Functions section in this chapter.

If a logic high level is present on an asynchronous external interrupt pin configured as “Interrupt on Rising Edge, Falling Edge, or Any Logic Change on Pin” while the external interrupt is not enabled, the corresponding external interrupt flag will be set when resuming from the above mentioned Sleep mode, as the clamping in these sleep mode produces the requested logic change.