ATtiny25 datasheet(52/196 Pages) ATMEL

52 / 196 page

7598H–AVR–07/09

ATtiny25/45/85

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, 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.

10.3

Alternate Port Functions

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

shows how the port pin control signals from the simplified Figure 10-2 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.

Figure 10-5. Alternate Port Functions

(1)

clk

RPx

RRx

WRx

RDx

WDx

PUD

SYNCHRONIZER

WDx:

WRITE DDRx

WRx:

WRITE PORTx

RRx:

READ PORTx REGISTER

RPx:

READ PORTx PIN

PUD:

PULLUP DISABLE

clk

I/O:

I/O CLOCK

RDx:

READ DDRx

SET

CLR

DIxn

AIOxn

DIEOExn

PVOVxn

PVOExn

DDOVxn

DDOExn

PUOExn

PUOVxn

PUOExn:

Pxn PULL-UP OVERRIDE ENABLE

PUOVxn:

Pxn PULL-UP OVERRIDE VALUE

DDOExn:

Pxn DATA DIRECTION OVERRIDE ENABLE

DDOVxn:

Pxn DATA DIRECTION OVERRIDE VALUE

PVOExn:

Pxn PORT VALUE OVERRIDE ENABLE

PVOVxn:

Pxn PORT VALUE OVERRIDE VALUE

DIxn:

DIGITAL INPUT PIN n ON PORTx

AIOxn:

ANALOG INPUT/OUTPUT PIN n ON PORTx

RESET

CLR

PINxn

PORTxn

DDxn

DIEOVxn

SLEEP

DIEOExn:

Pxn DIGITAL INPUT-ENABLE OVERRIDE ENABLE

DIEOVxn:

Pxn DIGITAL INPUT-ENABLE OVERRIDE VALUE

SLEEP:

SLEEP CONTROL

Pxn

I/O

PTOExn

PTOExn:

Pxn, PORT TOGGLE OVERRIDE ENABLE

WPx:

WRITE PINx

WPx

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