Datasheet

134
ATmega323(L)
1457E–11/01
I/O Ports All AVR ports have true Read-Modify-Write functionality when used as general digital
I/O ports. This means that the direction of one port pin can be changed without uninten-
tionally changing the direction of any other pin with the SBI and CBI instructions. The
same applies for changing drive value (if configured as output) or enabling/disabling of
pull-up resistors (if configured as input).
Port A Port A is an 8-bit bi-directional I/O port with optional internal pull-ups.
Three I/O memory address locations are allocated for Port A, one each for the Data
Register – PORTA, $1B($3B), Data Direction Register – DDRA, $1A($3A) and the Port
A Input Pins
– PINA, $19($39). The Port A Input Pins address is read only, while the
Data Register and the Data Direction Register are read/write.
All port pins have individually selectable pull-up resistors. The Port A output buffers can
sink 20 mA and thus drive LED displays directly. When pins PA0 to PA7 are used as
inputs and are externally pulled low, they will source current if the internal pull-up resis-
tors are activated.
Port A has an alternate function as analog inputs for the ADC. If some Port A pins are
configured as outputs, it is essential that these do not switch when a conversion is in
progress. This might corrupt the result of the conversion.
During power-down mode, the schmitt trigger of the digital input is disconnected. This
allows analog signals that are close to V
CC
/2 to be present during power-down without
causing excessive power consumption.
The Port A Data Register –
PORTA
The Port A Data Direction
Register – DDRA
The Port A Input Pins Address
– PINA
The Port A Input Pins address
– PINA – is not a register, and this address enables
access to the physical value on each Port A pin. When reading PORTA the Port A Data
Latch is read, and when reading PINA, the logical values present on the pins are read.
Port A as General Digital I/O All 8-bits in Port A are equal when used as digital I/O pins.
PAn, General I/O pin: The DDAn bit in the DDRA register selects the direction of this
pin, if DDAn is set (one), PAn is configured as an output pin. If DDAn is cleared (zero),
PAn is configured as an input pin. If PORTAn is set (one) when the pin configured as an
input pin, the MOS pull up resistor is activated. To switch the pull up resistor off, the
PORTAn has to be cleared (zero), the pin has to be configured as an output pin, or the
Bit 76543210
$1B ($3B)
PORTA7 PORTA6 PORTA5 PORTA4 PORTA3 PORTA2 PORTA1 PORTA0 PORTA
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Bit 76543210
$1A ($3A)
DDA7 DDA6 DDA5 DDA4 DDA3 DDA2 DDA1 DDA0 DDRA
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
Bit 76543210
$19 ($39)
PINA7 PINA6 PINA5 PINA4 PINA3 PINA2 PINA1 PINA0 PINA
Read/WriteRRRRRRRR
Initial Value N/A N/A N/A N/A N/A N/A N/A N/A