32
2466T–AVR–07/10
ATmega16(L)
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.
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 13 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.
tion. The figure is helpful in selecting an appropriate sleep mode.
MCU Control Register
– MCUCR
The MCU Control Register contains control bits for power management.
Bits 7, 5, 4 – SM2..0: Sleep Mode Select Bits 2, 1, and 0
These bits select between the six available sleep modes as shown in
Table 13.Note:
1. Standby mode and Extended Standby mode are only available with external crystals or
resonators.
Bit 6 – SE: Sleep Enable
The SE bit must be written to logic one to make the MCU enter the sleep mode when the SLEEP
instruction is executed. To avoid the MCU entering the sleep mode unless it is the programmers
purpose, it is recommended to write the Sleep Enable (SE) bit to one just before the execution of
the SLEEP instruction and to clear it immediately after waking up.
Bit
765
4321
0
SM2
SE
SM1
SM0
ISC11
ISC10
ISC01
ISC00
MCUCR
Read/Write
R/W
Initial Value
000
0000
0
Table 13. Sleep Mode Select
SM2
SM1
SM0
Sleep Mode
000
Idle
0
1
ADC Noise Reduction
010
Power-down
011
Power-save
100
Reserved
101
Reserved
110
1