Datasheet

35
ATmega48/88/168 Automotive [DATASHEET]
7530K–AVR–07/14
7.6 Standby Mode
When the SM2..0 bits are 110 and an external crystal/resonator clock option is selected, the SLEEP instruction makes the
MCU enter standby mode. This mode is identical to power-down with the exception that the oscillator is kept running. From
standby mode, the device wakes up in six clock cycles.
7.7 Power Reduction Register
The power reduction register, PRR, provides a method to stop the clock to individual peripherals to reduce power
consumption. The current state of the peripheral is frozen and the I/O registers can not be read or written. Resources used
by the peripheral when stopping the clock will remain occupied, hence the peripheral should in most cases be disabled
before stopping the clock. Waking up a module, which is done by clearing the bit in PRR, puts the module in the same state
as before shutdown.
Module shutdown can be used in idle mode and active mode to significantly reduce the overall power consumption. See
Section 28.1.1 “Power-Down Supply Current” on page 271 for examples. In all other sleep modes, the clock is already
stopped.
7.7.1 Power Reduction Register - PRR
• Bit 7 - PRTWI: Power Reduction TWI
Writing a logic one to this bit shuts down the TWI by stopping the clock to the module. When waking up the TWI again, the
TWI should be re-initialized to ensure proper operation.
• Bit 6 - PRTIM2: Power Reduction Timer/Counter2
Writing a logic one to this bit shuts down the Timer/Counter2 module in synchronous mode (AS2 is 0). When the
Timer/Counter2 is enabled, operation will continue like before the shutdown.
Table 7-2. Active Clock Domains and Wake-up Sources in the Different Sleep Modes.
Active Clock Domains Oscillators Wake-up Sources
Sleep Mode
clk
CPU
clk
FLASH
clk
IO
clk
ADC
clk
ASY
Main Clock
Source Enabled
Timer Oscillator
Enabled
INT1, INT0 and
Pin Change
TWI Address
Match
Timer2
SPM/EEPROM
Ready
ADC
WDT
OtherI/O
Idle X X X X X
(2)
X X X X X X X
ADC noise
reduction
X X X X
(2)
X
(3)
X X X X X
Power-down X
(3)
X X
Power-save X X X
(3)
X X X
Standby
(1)
X X
(3)
X X
Notes: 1. Only recommended with external crystal or resonator selected as clock source.
2. If Timer/Counter2 is running in asynchronous mode.
3. For INT1 and INT0, only level interrupt.
Bit 765432 1 0
PRTWI PRTIM2 PRTIM0 – PRTIM1 PRSPI PRUSART0 PRADC PRR
Read/Write R/W R/W R/W R R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0