Datasheet

35
2586N–AVR–04/11
ATtiny25/45/85
7. Power Management and Sleep Modes
The high performance and industry leading code efficiency makes the AVR microcontrollers an
ideal choise for low power applications. In addition, sleep modes enable the application to shut
down unused modules in the MCU, thereby saving power. The AVR provides various sleep
modes allowing the user to tailor the power consumption to the application’s requirements.
7.1 Sleep Modes
Figure 6-1 on page 23 presents the different clock systems and their distribution in
ATtiny25/45/85. The figure is helpful in selecting an appropriate sleep mode. Table 7-1 shows
the different sleep modes and their wake up sources.
Note: 1. For INT0, only level interrupt.
To enter any of the three sleep modes, the SE bit in MCUCR must be written to logic one and a
SLEEP instruction must be executed. The SM[1:0] bits in the MCUCR Register select which
sleep mode (Idle, ADC Noise Reduction or Power-down) will be activated by the SLEEP instruc-
tion. See Table 7-2 for a summary.
If an enabled interrupt occurs while the MCU is in a sleep mode, the MCU wakes up. The MCU
is then halted for four cycles in addition to the start-up time, executes the interrupt routine, and
resumes execution from the instruction following SLEEP. The contents of the Register File and
SRAM are unaltered when the device wakes up from sleep. If a reset occurs during sleep mode,
the MCU wakes up and executes from the Reset Vector.
Note that if a level triggered interrupt is used for wake-up the changed level must be held for
some time to wake up the MCU (and for the MCU to enter the interrupt service routine). See
“External Interrupts” on page 51 for details.
7.1.1 Idle Mode
When the SM[1:0] bits are written to 00, the SLEEP instruction makes the MCU enter Idle mode,
stopping the CPU but allowing Analog Comparator, ADC, USI, Timer/Counter, Watchdog, and
the interrupt system to continue operating. This sleep mode basically halts clk
CPU
and clk
FLASH
,
while allowing the other clocks to run.
Idle mode enables the MCU to wake up from external triggered interrupts as well as internal
ones like the Timer Overflow. If wake-up from the Analog Comparator interrupt is not required,
Table 7-1. 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
PCK
Main Clock Source Enabled INT0 and Pin Change SPM/EEPROM Ready USI Start Condition ADC Other I/O Watchdog Interrupt
Idle XXX X XXXXXX
ADC Noise
Reduction
XXX
(1)
XXX X
Power-down X
(1)
XX