ATmega88 datasheet(70/340 Pages) ATMEL

70 / 340 page

7530H–AVR–02/09

ATmega48/88/168 Automotive

10.3.1

MCU Control Register – MCUCR

• Bit 4 – PUD: Pull-up Disable

When this bit is written to one, the pull-ups in the I/O ports are disabled even if the DDxn and

PORTxn Registers are configured to enable the pull-ups ({DDxn, PORTxn} = 0b01). See “Con-

figuring the Pin” on page 64 for more details about this feature.

10.3.2

Alternate Functions of Port B

The Port B pins with alternate functions are shown in Table 10-3.

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.

Bit

–

–PUD

–

IVSEL

IVCE

MCUCR

Read/Write

R/W

Initial Value

Table 10-3.

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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