Datasheet

14. I/O-Ports

14.1. Overview

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 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 high sink and source capability. 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 V

and Ground as

indicated in the following figure.

Figure 14-1. I/O Pin Equivalent Schematic

Logic

See Figure

"General Digital I/O" for

Details

Pxn

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

Port B, here documented generally as PORTxn.

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. However, writing '1' to a bit in the

PINx Register will result in a toggle in the corresponding bit in the Data Register. In addition, 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 next section. 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 section in this chapter. Refer to the individual module

sections for a full description of the alternate functions.

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.

Atmel ATmega16M1/32M1/64M1 [DATASHEET]

Atmel-8209F-ATmega16M1/32M1/64M1_Datasheet_Complete-10/2016