Rainbow-electronics ATmega128RFA1 Uživatelský manuál stáhnout pdf (Strana 186)

186

8266A-MCU Wireless-12/09

ATmega128RFA1

14 I/O-Ports

14.1 Introduction

All ATmega128RFA1 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 unintentionally changing the direction of any other pin with the SBI and CBI

instructions. The same applies when changing drive value (if configured as output) or

enabling/disabling of pull-up resistors (if configured as input). Each output buffer has

symmetrical drive characteristics with both configurable sink and source capability.

Every port is individually configurable in four different drive strengths. The pin driver is

strong enough to drive LED displays directly. All port pins have individually selectable

pull-up resistors with a supply-voltage invariant resistance. All I/O pins have protection

diodes to both DEVDD and DVSS as indicated in

Figure 14-1 below. Refer to "Electrical

Characteristics" on page 501 for a complete list of parameters.

Figure 14-1. I/O Pin Equivalent Schematic

All registers and bit references in this section are written in general form. A lower case

“x” represents the numbering letter for the port, and a lower case “n” represents the bit

number. However, when using the register or bit defines in a program, the precise form

must be used. For example, PORTB3 for bit no. 3 in Port B, here documented generally

as PORTxn.

Three I/O memory address locations are allocated for each port, one each for the Data

The Port Input Pins I/O location is read only, while the Data Register and the Data

Direction Register are read/write. However, writing a logic one to a bit in the PINx

the Pull-up Disable – PUD bit in MCUCR disables the pull-up function for all pins in all

ports when set.

Using the I/O port as General Digital I/O is described in "Ports as General Digital I/O"

on page 187. Most port pins are multiplexed with alternate functions for the peripheral

features on the device. How each alternate function interferes with the port pin is

described in "Alternate Port Functions" on page 191. Refer to the individual module

sections for a full description of the alternate functions.

Note that enabling the alternate function of some of the port pins does not affect the use

of the other pins in the port as general digital I/O.

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