ATmega328P datasheet(82/448 Pages) ATMEL

82 / 448 page

8161D–AVR–10/09

ATmega48PA/88PA/168PA/328P

13.3.1

Alternate Functions of Port B

The Port B pins with alternate functions are shown in Table 13-3.

The alternate pin configuration is as follows:

• XTAL2/TOSC2/PCINT7 – 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) and the EXCLK bit is cleared (zero) to enable asynchronous clock-

ing of Timer/Counter2 using the Crystal Oscillator, pin PB7 is disconnected from the port, and

becomes the inverting output of the Oscillator amplifier. In this mode, a crystal Oscillator is con-

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

PCINT7: Pin Change Interrupt source 7. The PB7 pin can serve as an external interrupt source.

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

• XTAL1/TOSC1/PCINT6 – 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

Table 13-3.

Port B Pins Alternate Functions

Port Pin

Alternate Functions

PB7

XTAL2 (

Chip Clock Oscillator pin 2)

TOSC2 (

Timer Oscillator pin 2)

PCINT7 (Pin Change Interrupt 7)

PB6

XTAL1 (

Chip Clock Oscillator pin 1 or External clock input)

TOSC1 (

Timer Oscillator pin 1)

PCINT6 (Pin Change Interrupt 6)

PB5

SCK (SPI Bus Master clock Input)

PCINT5 (Pin Change Interrupt 5)

PB4

MISO (SPI Bus Master Input/Slave Output)

PCINT4 (Pin Change Interrupt 4)

PB3

MOSI (SPI Bus Master Output/Slave Input)

OC2A (Timer/Counter2 Output Compare Match A Output)

PCINT3 (Pin Change Interrupt 3)

PB2

SS (SPI Bus Master Slave select)

OC1B (Timer/Counter1 Output Compare Match B Output)

PCINT2 (Pin Change Interrupt 2)

PB1

OC1A (Timer/Counter1 Output Compare Match A Output)

PCINT1 (Pin Change Interrupt 1)

PB0

ICP1 (Timer/Counter1 Input Capture Input)

CLKO (Divided System Clock Output)

PCINT0 (Pin Change Interrupt 0)

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