Datasheet

61
ATmega48/88/168 Automotive [DATASHEET]
7530K–AVR–07/14
10.2.5 Digital Input Enable and Sleep Modes
As shown in Figure 10-2 on page 58, 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, power-save 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 also for these pins. SLEEP is also overridden by various other alternate functions as described in
Section 10.3 “Alternate Port Functions” on page 62.
If a logic high level (“one”) 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.
10.2.6 Unconnected Pins
If some pins are unused, it is recommended to ensure that these pins have a defined level. Even though most of the digital
inputs are disabled in the deep sleep modes as described above, floating inputs should be avoided to reduce current
consumption in all other modes where the digital inputs are enabled (reset, active mode and idle mode).
The simplest method to ensure a defined level of an unused pin, is to enable the internal pull-up. In this case, the pull-up will
be disabled during reset. If low power consumption during reset is important, it is recommended to use an external pull-up or
pull-down. Connecting unused pins directly to V
CC
or GND is not recommended, since this may cause excessive currents if
the pin is accidentally configured as an output.