Rainbow-electronics ATmega8515L Bedienungsanleitung PDF herunterladen (Seite 57)

ATmega8515(L)

2512A–AVR–04/02

Ports as General Digital

I/O

The ports are bi-directionalI/Oportswith optional internalpull-ups. Figure29shows a

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

Figure 29. GeneralDigitalI/O

(1)

Note: 1. WPx, WDx, RRx, RPx, and RDx are commontoall pinswithin the same port. clk

I/O

SLEEP, and PUD are common to all ports.

Configuring the Pin Each port pin consists of three registerbits: DDxn, PORTxn, and PINxn. Asshownin

“RegisterDescription forI/O Ports”onpage 72, the DDxn bits areaccessed at the DDRx

I/O address, thePORTxn bits at thePORTxI/O address, and thePINxn bits at thePINx

I/O address.

The DDxn bit in the DDRx Registerselects the direction of thispin. If DDxniswritten

logic one, Pxnisconfigured as an output pin. If DDxniswritten logiczero, Pxnisconfig-

ured as an input pin.

If PORTxniswritten a logic one when the pin isconfigured as an input pin, the pull-up

resistor is activated.Toswitch the pull-upresistor off, PORTxn has to be written a logic

zeroor the pin has to be configured as an output pin. The port pins aretri-statedwhen a

reset condition becomes active, even if no clocks are running.

If PORTxniswritten a logic one when the pin isconfigured as an output pin, the port pin

isdriven high(one). If PORTxniswritten a logiczero when the pin isconfigured as an

output pin, the port pin isdriven low(zero).

When switching between tri-state ({DDxn, PORTxn}=0b00) and output high({DDxn,

PORTxn}=0b11), an intermediate state with eitherpull-up enabled ({DDxn, PORTxn}=

0b01) or output low({DDxn, PORTxn}=0b10) mustoccur. Normally, the pull-up

clk

RPx

RRx

WPx

RDx

WDx

PUD

SYNCHRONIZER

WDx: WRITE DDRx

WPx: 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

DATA BUS

SLEEP

SLEEP: SLEEP CONTROL

Pxn

I/O

1 2 ... 52 53 54 55 56 57 58 59 60 61 62 ... 222 223

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