Datasheet

42
7728G–AVR–06/10
ATtiny87/ATtiny167
5. Power Management and Sleep Modes
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 consump-
tion to the application’s requirements.
When enabled, the Brown-out Detector (BOD) actively monitors the power supply voltage dur-
ing the sleep periods. To further save power, it is possible to disable the BOD in some sleep
modes. See “BOD Disable” on page 43 for more details.
5.1 Sleep Modes
Figure 4-1 on page 24 presents the different clock systems in the ATtiny87/167, and their dis-
tribution. The figure is helpful in selecting an appropriate sleep mode. Table 5-1 shows the
different sleep modes, their wake up sources and BOD disable ability.
Note: 1. For INT1 and INT0, only level interrupt.
To enter any of the four sleep modes, the SE bit in SMCR must be written to logic one and a
SLEEP instruction must be executed. The SM1, and SM0 bits in the SMCR Register select
which sleep mode (Idle, ADC Noise Reduction, Power-down, or Power-save) will be activated
by the SLEEP instruction. See Table 5-2 on page 47 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.
Table 5-1. Active Clock Domains and Wake-up Sources in the Different Sleep Modes
Active Clock Domains Oscillators Wake-up Sources
Software BOD Disable
Sleep Mode
clk
CPU
clk
FLASH
clk
IO
clk
ADC
clk
ASY
Main Clock Source Enabled Timer0 Osc. Enable INT1, INT0 and Pin Change SPM/EEPROM Ready ADC WDT USI Start Condition Timer0 Other I/O
Idle X X X X X X X XXXXX
ADC Noise
Reduction
XX X X X
(1)
X XXXX
Power-down X
(1)
XX X
Power-Save X X X
(1)
XXX X