Datasheet

Port Pin Alternate Functions

PB5 SCK (SPI Bus Master clock Input)

PB4 MISO (SPI Bus Master Input/Slave Output)

PB3 MOSI (SPI Bus Master Output/Slave Input)

OC2 (Timer/Counter2 Output Compare Match Output)

PB2 SS (SPI Bus Master Slave select)

OC1B (Timer/Counter1 Output Compare Match B Output)

PB1 OC1A (Timer/Counter1 Output Compare Match A Output)

PB0 ICP1 (Timer/Counter1 Input Capture Pin)

The alternate pin configuration is as follows:

• XTAL2/TOSC2 – Port B, Bit 7

XTAL2: Chip clock Oscillator pin 2. Used as clock pin for crystal Oscillator or Low-frequency crystal

Oscillator. When used as a clock pin, the pin can not be used as an I/O pin.

TOSC2: Timer Oscillator pin 2. Used only if internal calibrated RC Oscillator is selected as chip clock

source, and the asynchronous timer is enabled by the correct setting in ASSR. When the AS2 bit in

ASSR is set (one) to enable asynchronous clocking of Timer/Counter2, pin PB7 is disconnected from the

port, and becomes the inverting output of the Oscillator amplifier. In this mode, a crystal Oscillator is

connected to this pin, and the pin cannot be used as an I/O pin

If PB7 is used as a clock pin, DDB7, PORTB7 and PINB7 will all read 0.

• XTAL1/TOSC1 – Port B, Bit 6

XTAL1: Chip clock Oscillator pin 1. Used for all chip clock sources except internal calibrated RC

Oscillator. When used as a clock pin, the pin can not be used as an I/O pin.

TOSC1: Timer Oscillator pin 1. Used only if internal calibrated RC Oscillator is selected as chip clock

source, and the asynchronous timer is enabled by the correct setting in ASSR. When the AS2 bit in

ASSR is set (one) to enable asynchronous clocking of Timer/Counter2, pin PB6 is disconnected from the

port, and becomes the input of the inverting Oscillator amplifier. In this mode, a crystal Oscillator is

connected to this pin, and the pin can not be used as an I/O pin.

If PB6 is used as a clock pin, DDB6, PORTB6 and PINB6 will all read 0.

• SCK – Port B, Bit 5

SCK: Master Clock output, Slave Clock input pin for SPI channel. When the SPI is enabled as a Slave,

this pin is configured as an input regardless of the setting of DDB5. When the SPI is enabled as a Master,

the data direction of this pin is controlled by DDB5. When the pin is forced by the SPI to be an input, the

pull-up can still be controlled by the PORTB5 bit.

• MISO – Port B, Bit 4

MISO: Master Data input, Slave Data output pin for SPI channel. When the SPI is enabled as a Master,

this pin is configured as an input regardless of the setting of DDB4. When the SPI is enabled as a Slave,

the data direction of this pin is controlled by DDB4. When the pin is forced by the SPI to be an input, the

pull-up can still be controlled by the PORTB4 bit.

• MOSI/OC2 – Port B, Bit 3

AVR 8-Bit Microcontroller

I/O Ports

Datasheet Complete

40001974A-page 87