
69
ATmega64A [DATASHEET]
8160D–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.
14.2.3
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 Schmitt Trigger. The
signal denoted SLEEP in the figure, is set by the MCU Sleep Controller in Power-down mode, Power-save mode,
Standby mode, and Extended Standby mode to avoid high power consumption if some input signals are left float-
ing, 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
If a logic high level (“one”) is present on an asynchronous External Interrupt pin configured as “Interrupt on 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 modes, as the clamping in these sleep modes produces the
requested logic change.
14.2.4
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 VCC 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 shows how the port pin
control signals from the simplified
Figure 14-2 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.