65
ATmega165A/PA/325A/PA/3250A/PA/645A/P/6450A/P [DATASHEET]
8285E–AVR–02/2013
Note:
1. For the assembly program, two temporary registers are used to minimize the time from pull-ups are set on pins 0,
1, 6, and 7, until the direction bits are correctly set, defining bit 2 and 3 as low and redefining bits 0 and 1 as strong
high drivers.
14.2.5
Digital Input Enable and Sleep modes
As shown in
Figure 14-2, the digital input signal can be clamped to ground at the input of the Schmidt 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
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.
14.2.6
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.
14.3
Alternate port functions
Most port pins have alternate functions in addition to being general digital I/Os.
Figure 14-5 on page 66 shows how
the port pin control signals from the simplified
Figure 14-2 on page 62 can be overridden by alternate functions.
The overriding signals may not be present in all port pins, but the figure serves as a generic description applicable
to all port pins in the AVR microcontroller family.