14 i/o-ports, 1 introduction – Rainbow Electronics ATmega128RFA1 User Manual
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8266A-MCU Wireless-12/09
ATmega128RFA1
14 I/O-Ports
14.1 Introduction
All ATmega128RFA1 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 configurable sink and source capability.
Every port is individually configurable in four different drive strengths. 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 DEVDD and DVSS as indicated in
. Refer to
for a complete list of parameters.
Figure 14-1. I/O Pin Equivalent Schematic
All registers and bit references in this section are written in general form. A lower case
“x” represents the 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.
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
"Alternate Port Functions" on page 191
. 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.