Datasheet

• External level interrupt on INT
• Pin change interrupt
Note: 1. Timer/Counter will only keep running in asynchronous mode.
Related Links
8-bit Timer/Counter2 with PWM and Asynchronous Operation on page 188
11.6. Power-Down Mode
When the SM[2:0] 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 2-wire Serial
Interface address watch, and the Watchdog continue operating (if enabled).
Only one of these events can wake up the MCU:
• External Reset
• Watchdog System Reset
• Watchdog Interrupt
• Brown-out Reset
• 2-wire Serial Interface address match
• External level interrupt on INT
• Pin change interrupt
This sleep mode basically halts all generated clocks, allowing operation of asynchronous modules only.
Note: If a level triggered interrupt is used for wake-up from Power-Down, the required level must be held
long enough for the MCU to complete the wake-up to trigger the level interrupt. If the level disappears
before the end of the Start-up Time, the MCU will still wake up, but no interrupt will be generated. The
start-up time is defined by the SUT and CKSEL Fuses.
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.
Related Links
Clock Sources on page 43
EXINT - External Interrupts on page 83
11.7. Power-Save Mode
When the SM[2:0] bits are written to 011, the SLEEP instruction makes the MCU enter Power-save mode.
This mode is identical to Power-down, except:
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
Timer/Counter2 is not using the asynchronous clock, the Timer/Counter Oscillator is stopped during
sleep. If Timer/Counter2 is not using the synchronous clock, the clock source is stopped during sleep.
Even if the synchronous clock is running in Power-save, this clock is only available for Timer/Counter2.
Atmel ATmega644A [DATASHEET]
Atmel-42716C-ATmega644A_Datasheet_Complete-10/2016
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