ATmega16 datasheet(50/357 Pages) ATMEL

50 / 357 page

2466S–AVR–05/09

ATmega16(L)

I/O Ports

Introduction

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 unintentionally changing

the direction of any other pin with the SBI and CBI instructions. The same applies when chang-

ing 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 high sink and source

capability. The pin driver is strong enough to drive LED displays directly. All port pins have indi-

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

protection diodes to both V

CC and Ground as indicated in Figure 22. Refer to “Electrical Charac-

teristics” on page 291 for a complete list of parameters.

Figure 22. I/O Pin Equivalent Schematic

All registers and bit references in this section are written in general form. A lower case “x” repre-

sents 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. i.e., PORTB3

for bit no. 3 in Port B, here documented generally as PORTxn. The physical I/O Registers and

bit locations are listed in “Register Description for I/O Ports” on page 66.

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

– PORTx, Data Direction Register – DDRx, and the Port Input Pins – PINx. The Port Input Pins

I/O location is read only, while the Data Register and the Data Direction Register are read/write.

In addition, the Pull-up Disable – PUD bit in SFIOR 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

50. 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 55. Refer to the individual module sections for a full description of the alter-

nate 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.

Ports as General

Digital I/O

The ports are bi-directional I/O ports with optional internal pull-ups. Figure 23 shows a functional

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

Logic

See Figure 23

"General Digital I/O" for

Details

Pxn

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