45
7734Q–AVR–02/12
AT90PWM81/161
6.
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.
6.1
Sleep Modes
distribution. The figure is helpful in selecting an appropriate sleep mode.
Table 6-1 shows the
different sleep modes, their wake up sources.
Notes:
1. Only recommended with external crystal or resonator selected as clock source.
2. Only level interrupt.
To enter any of the five sleep modes, the SE bit in SMCR must be written to logic one and a
SLEEP instruction must be executed. The SM2, SM1, and SM0 bits in the SMCR Register select
which sleep mode (Idle, ADC Noise Reduction, Power-down or Standby) will be activated by the
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.
6.2
Idle Mode
When the SM2..0 bits are written to 000, the SLEEP instruction makes the MCU enter Idle
mode, stopping the CPU but allowing SPI, Analog Comparator, ADC, Timer/Counters, Watch-
dog, and the interrupt system to continue operating. This sleep mode basically halt 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 interrupts. If wake-up from the Analog Comparator interrupt is not
required, the Analog Comparator can be powered down by clearing the ACnEN bit in the Analog
Comparator Control and Status Register – ACnCON. This will reduce power consumption in Idle
mode. If the ADC is enabled, a conversion starts automatically when this mode is entered.
Table 6-1.
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
cl
k
IO
clk
ADC
clk
PLL
Main
cloc
k
source
en
ab
le
d
IN
T
3
..0
PSC
SPM/EEPR
OM
ready
ADC
WDT
Ot
her/
O
Idle
X
ADC noise
reduction
XX
X
XX
X
Power-
down
X
X