ATMEGA6450_14 Datasheet, PDF (60/362 Pages) ATMEL Corporation – High Endurance Non-volatile Memory Segments

ATmega325/3250/645/6450
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 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. Port B has a higher pin driver strength than the other ports, but all the pin drivers are
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 14-1. Refer to “Electrical Characteristics” on page 297 for
a complete list of parameters. If exceeding the pin voltage “Absolute Maximum Ratings”, result-
ing currents can harm the device if not limited accordingly. For segment pins used as general
I/O, the same situation can also influence the LCD voltage level.
Figure 14-1. I/O Pin Equivalent Schematic
2570N–AVR–05/11
Pxn
C_pin
R_pu
Logic
See Figure
"General Digital I/O" for
Details
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. For example,
PORTB3 for bit no. 3 in Port B, here documented generally as PORTxn. The physical I/O Regis-
ters and bit locations are listed in “Register Description” on page 81.
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 Register, will result in a toggle in the correspond-
ing 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
61. 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
60