ATMEGA8U2_14 Datasheet, PDF (72/310 Pages) ATMEL Corporation – 125 Powerful Instructions – Most Single Clock Cycle Execution

ATmega8U2/16U2/32U2
12.2.6
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 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.
12.3
Alternate Port Functions
Most port pins have alternate functions in addition to being general digital I/Os. Figure 12-5
shows how the port pin control signals from the simplified Figure 12-2 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 12-5. Alternate Port Functions⁽¹⁾
PUOExn
PUOVxn
1
0
PUD
DDOExn
DDOVxn
1
0
PVOExn
PVOVxn
QD
DDxn
Q CLR
RESET
WDx
RDx
1
Pxn
0
1
QD
0
PORTxn
PTOExn
DIEOExn
Q CLR
DIEOVxn
1
0
SLEEP
RESET
RRx
WRx
WPx
SYNCHRONIZER
D ^SET Q
L CLR Q
DQ
PINxn
CLR Q
RPx
clk _I/O
DIxn
PUOExn:
PUOVxn:
DDOExn:
DDOVxn:
PVOExn:
PVOVxn:
DIEOExn:
DIEOVxn:
SLEEP:
PTOExn:
Pxn PULL-UP OVERRIDE ENABLE
Pxn PULL-UP OVERRIDE VALUE
Pxn DATA DIRECTION OVERRIDE ENABLE
Pxn DATA DIRECTION OVERRIDE VALUE
Pxn PORT VALUE OVERRIDE ENABLE
Pxn PORT VALUE OVERRIDE VALUE
Pxn DIGITAL INPUT-ENABLE OVERRIDE ENABLE
Pxn DIGITAL INPUT-ENABLE OVERRIDE VALUE
SLEEP CONTROL
Pxn, PORT TOGGLE OVERRIDE ENABLE
PUD:
WDx:
RDx:
RRx:
WRx:
RPx:
WPx:
clk_I/O:
DIxn:
AIOxn:
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
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