Alternate Port Functions - Atmel ATtiny25 Manual

10.2.6 Unconnected Pins
10.3

Alternate Port Functions

ATtiny25/45/85
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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 or GND is not recommended, since this may cause excessive currents if the pin is
CC
accidentally configured as an output.
Most port pins have alternate functions in addition to being general digital I/Os.
shows how the port pin control signals from the simplified
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
Pxn
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
DIEOExn: Pxn DIGITAL INPUT-ENABLE OVERRIDE ENABLE
DIEOVxn: Pxn DIGITAL INPUT-ENABLE OVERRIDE VALUE
SLEEP: SLEEP CONTROL
PTOExn: Pxn, PORT TOGGLE OVERRIDE ENABLE
(1)
PUOExn
PUOVxn
1
0
DDOExn
DDOVxn
1
0
PVOExn
PVOVxn
1
0
PORTxn
DIEOExn
DIEOVxn RESET
1
SLEEP
0
SYNCHRONIZER
SET
D Q
D Q
PINxn
L Q Q
CLR CLR
PUD:
WDx:
RDx:
RRx:
WRx:
RPx:
WPx:
clk :
I/O
DIxn:
AIOxn:
Figure 10-2 can be overridden by
PUD
Q D
DDxn
Q
CLR
WDx
RESET
RDx
1
Q D
0
PTOExn
Q
CLR
WRx
RRx
RPx
clk
I/O
DIxn
AIOxn
PULLUP DISABLE
WRITE DDRx
READ DDRx
READ PORTx REGISTER
WRITE PORTx
READ PORTx PIN
WRITE PINx
I/O CLOCK
DIGITAL INPUT PIN n ON PORTx
ANALOG INPUT/OUTPUT PIN n ON PORTx
Figure 10-5
WPx
7598H–AVR–07/09