46
ATtiny26(L)
1477G–AVR–03/05
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
pullup. In this case, the pullup will be disabled during reset. If low power consumption
during reset is important, it is recommended to use an external pullup or pulldown. Con-
necting 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.
Alternate Port Functions Most port pins have alternate functions in addition to being general digital I/Os. Figure
35 shows how the port pin control signals from the simplified Figure 32 can be overrid-
den 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 micro-
controller family.
Figure 35. Alternate Port Functions
(1)
Note: 1. WPx, WDx, RLx, RPx, and RDx are common to all pins within the same port. clk
I/O
,
SLEEP, and PUD are common to all ports. All other signals are unique for each pin.
clk
RPx
RRx
WPx
RDx
WDx
PUD
SYNCHRONIZER
WDx: WRITE DDRx
WPx: WRITE PORTx
RRx: READ PORTx REGISTER
RPx: READ PORTx PIN
PUD: PULLUP DISABLE
clk
I/O
: I/O CLOCK
RDx: READ DDRx
D
L
Q
Q
SET
CLR
0
1
0
1
0
1
DIxn
AIOxn
DIEOExn
PVOVxn
PVOExn
DDOVxn
DDOExn
PUOExn
PUOVxn
UOExn: Pxn PULL-UP OVERRIDE ENABLE
UOVxn: Pxn PULL-UP OVERRIDE VALUE
DOExn: Pxn DATA DIRECTION OVERRIDE ENABLE
DOVxn: Pxn DATA DIRECTION OVERRIDE VALUE
VOExn: Pxn PORT VALUE OVERRIDE ENABLE
VOVxn: Pxn PORT VALUE OVERRIDE VALUE
DIxn: DIGITAL INPUT PIN n ON PORTx
AIOxn: ANALOG INPUT/OUTPUT PIN n ON PORT
RESET
RESET
Q
Q
D
CLR
Q
Q
D
CLR
Q
Q
D
CLR
PINxn
PORTxn
DDxn
DATA BUS
0
1
DIEOVxn
SLEEP
IEOExn: Pxn DIGITAL INPUT-ENABLE OVERRIDE ENABLE
IEOVxn: Pxn DIGITAL INPUT-ENABLE OVERRIDE VALUE
LEEP: SLEEP CONTROL
Pxn
I/O
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