ATmega16HVB datasheet(67/273 Pages) ATMEL

67 / 273 page

8042A–AVR–07/09

ATmega16HVB/32HVB

15. Low Voltage I/O-Ports

15.1

Overview

All low voltage AVR ports have true Read-Modify-Write functionality when used as general digi-

tal 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). 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 V

REG and Ground

as indicated in Figure 15-1. Refer to ”Electrical Characteristics” on page 228 for a complete list

of parameters.

Figure 15-1. Low Voltage I/O Pin Equivalent Schematic

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 78.

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 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 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 68. 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 72. Refer to the individual module sections for a

full description of the alternate functions.

Logic

See Figure

"General Digital I/O" for

Details

Pxn

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