ATmega169P datasheet(42/393 Pages) ATMEL

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8018N–AVR–08/09

ATmega169P

9.5

Power-save Mode

When the SM2..0 bits are written to 011, the SLEEP instruction makes the MCU enter Power-

save mode. This mode is identical to Power-down, with one exception:

If Timer/Counter2 and/or the LCD controller are enabled, they will keep running during sleep.

The device can wake up from either Timer Overflow or Output Compare event from

Timer/Counter2 if the corresponding Timer/Counter2 interrupt enable bits are set in TIMSK2,

and the Global Interrupt Enable bit in SREG is set. It can also wake up from an LCD controller

interrupt.

If neither Timer/Counter2 nor the LCD controller is running, Power-down mode is recommended

instead of Power-save mode.

The LCD controller and Timer/Counter2 can be clocked both synchronously and asynchronously

in Power-save mode. The clock source for the two modules can be selected independent of

each other. If neither the LCD controller nor the Timer/Counter2 is using the asynchronous

clock, the Timer/Counter Oscillator is stopped during sleep. If neither the LCD controller nor the

Timer/Counter2 is using the synchronous clock, the clock source is stopped during sleep. Note

that even if the synchronous clock is running in Power-save, this clock is only available for the

LCD controller and Timer/Counter2.

9.6

Standby Mode

When the SM2..0 bits are 110 and an external crystal/resonator clock option is selected, the

SLEEP instruction makes the MCU enter Standby mode. This mode is identical to Power-down

with the exception that the Oscillator is kept running. From Standby mode, the device wakes up

in six clock cycles.

9.7

Power Reduction Register

The Power Reduction Register (PRR), see ”PRR – Power Reduction Register” on page 45, pro-

vides a method to stop the clock to individual peripherals to reduce power consumption. The

current state of the peripheral is frozen and the I/O registers can not be read or written.

Resources used by the peripheral when stopping the clock will remain occupied, hence the

peripheral should in most cases be disabled before stopping the clock. Waking up a module,

which is done by clearing the bit in PRR, puts the module in the same state as before shutdown.

Module shutdown can be used in Idle mode and Active mode to significantly reduce the overall

power consumption. See ”Supply Current of I/O modules” on page 341 for examples. In all other

sleep modes, the clock is already stopped.

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