Rainbow Electronics ATmega8HVD - Manual (Page 61)

61
8052B–AVR–09/08
ATmega4HVD/8HVD
14. Low Voltage I/O-Ports
14.1 Overview
All low voltage 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 uninten-
tionally 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). All low voltage 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 14-1 . Refer to ”Electrical Characteristics” on page 142
for a complete list of parameters.
Figure 14-1. Low Voltage I/O Pin Equivalent Schematic
Note: See Figure 14-2 on page 62 for details.
All registers and bit references in this section are written in general form. A lower case “x” rep-
resents 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 70 .
Three I/O memory address locations are allocated for each low voltage 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 Regis-
ter 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 low voltage pins in all ports when set.
Using the I/O port as General Digital I/O is described in ”Low Voltage Ports as General Digital
I/O” on page 62 . Many low voltage 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 66 . Refer to the individual module sections for
a full description of the alternate functions.
C
pin
Logic
R
pu
Pxn