Datasheet

59
ATtiny828 [DATASHEET]
8371A–AVR–08/12
10. I/O Ports
10.1 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.
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 21 on page 59. See “Electrical Characteristics” on page 247 for a complete list of parameters.
Figure 21. I/O Pin Equivalent Schematic
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” on page 81.
Four I/O memory address locations are allocated for each port, one each for the Data Register – PORTx, Data Direction
Register – DDRx, Pull-up Enable Register – PUEx, and the Port Input Pins – PINx. The Port Input Pins I/O location is
read only, while the Data Register, the Data Direction Register, and the Pull-up Enable 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.
Using the I/O port as General Digital I/O is described in “Ports as General Digital I/O” on page 59. Most port pins are
multiplexed with alternative functions for the peripheral features on the device. How each alternative function interferes
with the port pin is described in “Alternative Port Functions” on page 63. Refer to the individual module sections for a full
description of the alternative functions.
Note that enabling the alternative function of some of the port pins does not affect the use of the other pins in the port as
general digital I/O.
10.2 Ports as General Digital I/O
The ports are bi-directional I/O ports with optional internal pull-ups. Figure 22 shows a functional description of one I/O-
port pin, here generically called Pxn.
C
pin
Logic
R
pu
See Figure
"General Digital I/O" for
Details
Pxn