ATTINY26L8SU SL383 Atmel, ATTINY26L8SU SL383 Datasheet - Page 44

• Manufacturer Part Number: ATTINY26L8SU SL383
• Description: MCU 8-Bit ATtiny AVR RISC 2KB Flash 3.3V/5V 20-Pin SOIC T/R
• Manufacturer: Atmel

Ports as General Digital
I/O
Configuring the Pin
44
ATtiny26(L)
The ports are bi-directional I/O ports with optional internal pull-ups. Figure 32 shows a
functional description of one I/O-port pin, here generically called Pxn.
Figure 32. General Digital I/O
Note:
Each port pin consists of 3 Register bits: DDxn, PORTxn, and PINxn. As shown in “Reg-
ister Description for I/O Ports” on page 58, 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 config-
ured 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 a
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 out-
put 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, PORTxn} = 0b10) must occur. Normally, the pull-up
enabled state is fully acceptable, as a high-impedant environment will not notice the
Pxn
1. WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clk
SLEEP, and PUD are common to all ports.
PUD:
SLEEP:
clk
I/O
:
PULLUP DISABLE
SLEEP CONTROL
I/O CLOCK
(1)
SLEEP
SYNCHRONIZER
WDx:
RDx:
WPx:
RRx:
RPx:
D
L
Q
Q
D
PINxn
WRITE DDRx
READ DDRx
WRITE PORTx
READ PORTx REGISTER
READ PORTx PIN
Q
Q
RESET
RESET
PORTxn
Q
Q
Q
Q
DDxn
CLR
CLR
D
D
PUD
WDx
RDx
WPx
RRx
RPx
clk
I/O
1477J–AVR–06/07
I/O
,