40
8271D–AVR–05/11
ATmega48A/PA/88A/PA/168A/PA/328/P
10. 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.
See
10.1
Sleep Modes
F i g u r e 9 - 1 o n p a g e 2 7
p r e s e n t s t h e d i f f e r e n t c l o c k s y s t e m s i n t h e
ATmega48A/PA/88A/PA/168A/PA/328/P, and their distribution. The figure is helpful in selecting
an appropriate sleep mode.
shows the different sleep modes, their wake up sources
Note:
1. BOD disable is only available for ATmega48PA/88PA/168PA/328P.
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.
To enter any of the six 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, Power-save, Standby, or Extended
Standby) will be activated by the SLEEP instruction. See
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 10-1.
Active Clock Domains and Wake-up Sources in the Different Sleep Modes.
Active Clock Domains
Oscillators
Wake-up Sources
Softw
a
re
BOD Disa
b
le
Sleep Mode
clk
CP
U
clk
FLASH
clk
IO
clk
AD
C
clk
AS
Y
Ma
in Clo
c
k
Source Enab
led
T
imer
Os
cillator
Enab
le
d
INT
1
, INT
0
and
Pin Chan
ge
TW
I Addre
s
s
Ma
tc
h
Time
r2
SP
M/EEPR
OM
Read
y
ADC
WDT
Other I/O
Idle
X
X
X
X
X
X
X
X
X
X
X
X
ADC Noise
Reduction
X
X
X
X
X
X
X
X
X
Power-down
X
X
X
X
Power-save
X
X
X
X
X
X
X
Standby
X
X
X
X
X
Extended
Standby
X
X
X
X
X
X
X
X