70
7530J–AVR–03/12
Atmel 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-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
7
6
5
4
3
2
1
0
–
–PUD
–
IVSEL
IVCE
MCUCR
Read/Write
R
R/W
R
R/W
Initial Value
0
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)