ATmega16 datasheet(32/357 Pages) ATMEL

32 / 357 page

2466S–AVR–05/09

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.

Figure 11 on page 24 presents the different clock systems in the ATmega16, and their distribu-

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

SM2

SM1

SM0

ISC11

ISC10

ISC01

ISC00

MCUCR

Read/Write

R/W

Initial Value

000

0000

Table 13. Sleep Mode Select

SM2

SM1

SM0

Sleep Mode

000

Idle

ADC Noise Reduction

010

Power-down

011

Power-save

100

Reserved

101

Reserved

110

Standby(1)

Extended Standby(1)

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