Datasheet

ATmega164A/PA/324A/PA/644A/PA/1284/P
 2018 Microchip Technology Inc. Data Sheet Complete DS40002070A-page 52
10.6 Power-down mode
When the SM2..0 bits are written to 010, the SLEEP instruction makes the MCU enter Power-down mode. In
this mode, the external Oscillator is stopped, while the external interrupts, the two-wire Serial Interface, and the
Watchdog continue operating (if enabled). Only an External Reset, a Watchdog Reset, a Brown-out Reset, two-
wire Serial Interface address match, an external interrupt on INT2:0, or a pin change interrupt can wake up the
MCU. This sleep mode basically halts all generated clocks, allowing operation of asynchronous modules only.
Note that if a level triggered interrupt is used for wake-up from Power-down mode, the changed level must be
held for some time to wake up the MCU. Refer to ”External Interrupts” on page 75 for details.
When waking up from Power-down mode, there is a delay from the wake-up condition occurs until the wake-up
becomes effective. This allows the clock to restart and become stable after having been stopped. The wake-up
period is defined by the same CKSEL Fuses that define the Reset Time-out period, as described in ”Clock
Sources” on page 39.
10.7 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 is enabled, it 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.
If Timer/Counter2 is not running, Power-down mode is recommended instead of Power-save mode.
The Timer/Counter2 can be clocked both synchronously and asynchronously in Power-save mode. If the
Timer/Counter2 is not using the asynchronous clock, the Timer/Counter Oscillator is stopped during sleep. If the
Timer/Counter2 is not 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 Timer/Counter2.
10.8 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.33
10.9 Extended Standby mode
When the SM2..0 bits are 111 and an external crystal/resonator clock option is selected, the SLEEP instruction
makes the MCU enter Extended Standby mode. This mode is identical to Power-save mode with the exception
that the Oscillator is kept running. From Extended Standby mode, the device wakes up in six clock cycles.