AT90SCR100 datasheet(75/433 Pages) ATMEL

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AT90SCR100

12. I/O Ports

12.1

Standard IO Ports

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 chang-

ing 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. The pin driver is strong enough to drive LED displays directly. All port pins have indi-

vidually 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 12-1. Refer to “Electrical Char-

acteristics” on page 409 for a complete list of parameters.

Figure 12-1.

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 reference 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 for I/O-Ports” on page 83.

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 correspond-

ing 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” on page

77. Most port pins are multiplexed with alternate functions for the peripheral features on the

device. To get a full description of the different pin configuration, refer to “Pin List Configuration”

on page 5.

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.

Logic

See Figure

"General Digital I/O" for

Details

Pxn

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