
32
8154B–AVR–07/09
ATmega16A
9.
Power Management and Sleep Modes
9.1
Overview
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.
9.2
Sleep Modes
bution. The figure is helpful in selecting an appropriate sleep mode.
Table 9-1 shows the
different sleep modes and their wake-up sources.
Notes:
1. External Crystal or resonator selected as clock source.
2. If AS
2 bit in ASSR is set.
3. Only INT2 or level interrupt INT1 and INT0.
To enter any of the six sleep modes, the SE bit in MCUCR must be written to logic one and a
SLEEP instruction must be executed. The SM2, SM1, and SM0 bits in the MCUCR 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
Table 9-2 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, it 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 9-1.
Active Clock Domains and Wake Up Sources in the Different Sleep Modes
Active Clock domains
Oscillators
Wake-up Sources
Sleep Mode
clk
CP
U
clk
FLA
SH
cl
k
IO
clk
AD
C
clk
AS
Y
Main
C
loc
k
Sour
ce
Enab
led
Tim
e
rOs
c.
Enab
led
INT
2
,INT
1
,INT
0
T
W
IAd
dress
Matc
h
Tim
e
r2
SPM
/
EEPR
O
M
R
ead
y
ADC
Oth
e
rI/O
Idle
X
XXXX
X
ADC NRM
X
XXX
X
Power Down
X
Power Save
X
Extended