Datasheet

/* Insert nop for synchronization*/
__no_operation();
/* Read port pins */
i = PINB;
...
18.2.5 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.
18.2.6 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.
18.3 Alternate Port Functions
Most port pins have alternate functions in addition to being general digital I/Os. The following figure
shows how the port pin control signals from the simplified Figure 18-2 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.
ATmega48PA/88PA/168PA
I/O-Ports
© 2018 Microchip Technology Inc.
Datasheet Complete
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