9.
I/O-Ports
9.1
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/disabling of pull-up resistors
(if configured as input). Each output buffer has symmetrical drive characteristics with both high sink and source capability. All
port pins have individually selectable pull-up resistors with a supply-voltage invariant resistance. All I/O pins have protection
diodes to both VCC and ground as indicated in Figure 9-1. Refer to Section 26. “Electrical Characteristics” on page 273 for a
complete list of parameters.
Figure 9-1. I/O Pin Equivalent Schematic
Rpu
Pxn
Logic
See Figure
”General Digital I/O”
for Details
Cpin
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. The
physical I/O registers and bit locations are listed in “Register Description for I/O-Ports”.
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
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”. 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 Section 9.3 “Alternate Port Functions” on page 55. 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.
ATmega16/32/64/M1/C1 [DATASHEET]
51
7647O–AVR–01/15
MICROCHIP [ MICROCHIP ]
