Datasheet

Electrical Characteristics on page 359
17.2. Ports as General Digital I/O
The ports are bi-directional I/O ports with optional internal pull-ups. The following figure shows a
functional description of one I/O-port pin, here generically called Pxn.
Figure 17-2. General Digital I/O
(1)
clk
RPx
RRx
RDx
WDx
PUD
SYNCHRONIZER
WDx: WRITE DDRx
RRx: READ PORTx REGISTER
RPx: READ PORTx PIN
PUD: PULLUP DISABLE
clk
I/O
: I/O CLOCK
RDx: READ DDRx
D
L
Q
Q
RESET
RESET
Q
QD
Q
Q D
CLR
PORTxn
Q
Q D
CLR
DDxn
PINxn
DATA BUS
SLEEP
SLEEP: SLEEP CONTROL
Pxn
I/O
WPx
WPx: WRITE PINx REGISTER
Note: 1. WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clk
I/O
, SLEEP,
and PUD are common to all ports
17.2.1. Configuring the Pin
Each port pin consists of three register bits: DDxn, PORTxn, and PINxn. As shown in Register
Description, the DDxn bits are accessed at the DDRx I/O address, the PORTxn bits at the PORTx I/O
address, and the PINxn bits at the PINx I/O address.
The DDxn bit in the DDRx Register selects the direction of this pin. If DDxn is written logic one, Pxn is
configured as an output pin. If DDxn is written logic zero, Pxn is configured as an input pin.
If PORTxn is written logic one when the pin is configured as an input pin, the pull-up resistor is activated.
To switch the pull-up resistor off, PORTxn has to be written logic zero or the pin has to be configured as
an output pin. The port pins are tri-stated when reset condition becomes active, even if no clocks are
running.
If PORTxn is written logic one when the pin is configured as an output pin, the port pin is driven high
(one). If PORTxn is written logic zero when the pin is configured as an output pin, the port pin is driven
low (zero).
When switching between tri-state ({DDxn, PORTxn} = 0b00) and output high ({DDxn, PORTxn} = 0b11),
an intermediate state with either pull-up enabled ({DDxn, PORTxn} = 0b01) or output low ({DDxn,
Atmel ATmega32A [DATASHEET]
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