Datasheet

67
ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]
2549Q–AVR–02/2014
13. I/O-Ports
13.1 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 changing drive value (if configured as output) or enabling/dis-
abling 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
CC
and Ground as indicated in Figure 13-1. Refer to “Electrical Characteristics” on page 355 for a
complete list of parameters.
Figure 13-1. I/O Pin Equivalent Schematic
All registers and bit references in this section are written in general form. A lower case “x” represents the number-
ing 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 docu-
mented generally as PORTxn. The physical I/O Registers and bit locations are listed in “Table 13-34 and Table 13-
35 relates the alternate functions of Port L to the overriding signals shown in Figure 13-5 on page 73.” on page 95.
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. However, writing a logic one to a bit in the PINx Reg-
ister, 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 “Ports as General Digital I/O” on page 68. Most port pins
are multiplexed with alternate functions for the peripheral features on the device. How each alternate function inter-
feres with the port pin is described in “Alternate Port Functions” on page 72. 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.
C
pin
Logic
R
pu
See Figure
"General Digital I/O" for
Details
Pxn