AT90PWM2 datasheet(40/361 Pages) ATMEL

40 / 361 page

4317J–AVR–08/10

AT90PWM2/3/2B/3B

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 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, Power-save, or Standby) will be

activated by the SLEEP instruction. See Table 8-1 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 exe-

cutes from the Reset Vector.

Figure 7-1 on page 28 presents the different clock systems in the AT90PWM2/2B/3/3B, and their

distribution. The figure is helpful in selecting an appropriate sleep mode.

8.1

Sleep Mode Control Register – SMCR

The Sleep Mode Control Register contains control bits for power management.

• Bits 3..1 – SM2..0: Sleep Mode Select Bits 2, 1, and 0

These bits select between the five available sleep modes as shown in Table 8-1.

Note:

1. Standby mode is only recommended for use with external crystals or resonators.

• Bit 1 – 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 programmer’s

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.

8.2

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, USART, Analog Comparator, ADC, Timer/Counters,

Bit

76543210

–

SM2

SM1

SM0

SMCR

Read/Write

RRRR

R/W

Initial Value

00000000

Table 8-1.

Sleep Mode Select

SM2

SM1

SM0

Sleep Mode

000

Idle

ADC Noise Reduction

010

Power-down

011

Reserved

100

Reserved

101

Reserved

110

Standby(1)

111

Reserved

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