ATtiny44 datasheet(55/236 Pages) ATMEL

55 / 236 page

8006H–AVR–10/09

ATtiny24/44/84

10.1

Ports as General Digital I/O

The ports are bi-directional I/O ports with optional internal pull-ups. Figure 10-2 shows a func-

tional description of one I/O-port pin, here generically called Pxn.

Figure 10-2. General Digital I/O

(1)

Note:

1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clkI/O,

SLEEP, and PUD are common to all ports.

10.1.1

Configuring the Pin

Each port pin consists of three register bits: DDxn, PORTxn, and PINxn. As shown in “Register

Description” on page 67, 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).

clk

RPx

RRx

RDx

WDx

PUD

SYNCHRONIZER

WDx:

WRITE DDRx

WRx:

WRITE PORTx

RRx:

READ PORTx REGISTER

RPx:

READ PORTx PIN

PUD:

PULLUP DISABLE

clk

I/O:

I/O CLOCK

RDx:

READ DDRx

RESET

CLR

PORTxn

CLR

DDxn

PINxn

SLEEP

SLEEP:

SLEEP CONTROL

Pxn

I/O

WPx

WRx

WPx:

WRITE PINx REGISTER

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