ATtiny44 datasheet(58/236 Pages) ATMEL

58 / 236 page

8006H–AVR–10/09

ATtiny24/44/84

Note:

See “Code Examples” on page 6.

10.1.5

Digital Input Enable and Sleep Modes

As shown in Figure 10-2 on page 55, 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 and Standby modes 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 “Alternate Port Functions” on page 58.

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.

10.1.6

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, float-

ing 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 pulldown. 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.

10.2

Alternate Port Functions

Most port pins have alternate functions in addition to being general digital I/Os. In Figure 10-5

below is shown how the port pin control signals from the simplified Figure 10-2 on page 55 can

be overridden by alternate functions.

C Code Example

unsigned char

...

/* Define pull-ups and set outputs high */

/* Define directions for port pins */

PORTA = (1<<PA4)|(1<<PA1)|(1<<PA0);

DDRA = (1<<DDA3)|(1<<DDA2)|(1<<DDA1)|(1<<DDA0);

/* Insert nop for synchronization*/

_NOP();

/* Read port pins */

i = PINA;

...

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