36
8008H–AVR–04/11
ATtiny48/88
7.
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 during
the sleep periods. To further save power, it is possible to disable the BOD in some sleep modes.
7.1
Sleep Modes
tion. The figure is helpful in selecting an appropriate sleep mode.
Table 7-1 shows the different
sleep modes, their wake up sources and the BOD disable ability.
Notes:
1. For INT1 and INT0, only level interrupt
To enter any of the 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, or Power-down) will be activated by the SLEEP instruction.
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
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 the SPI, Analog Comparator, ADC, 2-wire Serial Interface,
Timer/Counters, Watchdog, and the interrupt system to continue operating. This sleep mode
basically halts clk
CPU and clkFLASH, while allowing the other clocks to run.
Table 7-1.
Active Clock Domains and Wake-up Sources in the Different Sleep Modes
Sleep Mode
Active Clock Domain
Oscillator
Wake-up Source
clk
CPU
clk
FL
AS
H
clk
IO
clk
ADC
Mai
n
Cloc
k
So
urce
En
ab
le
d
INT1,
INT0
and
Pi
n
C
hang
e
TWI
Address
Match
EEPR
OM
R
eady
ADC
WDT
Other
I/O
Idle
X
XX
X
ADC Noise Reduction
X
XX
Power-down
XX