ATmega64A
9.3
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 address watch, and the Watchdog continue operating (if enabled).
Only an External Reset, a Watchdog Reset, a Brown-out Reset, a Two-wire Serial Interface
address match interrupt, an external level interrupt on INT7:4, or an External Interrupt on INT3:0
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 “8-bit Timer/Counter0 with PWM
and Asynchronous Operation” on page 92 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 38.
9.4
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/Counter0 is clocked asynchronously (i.e., the AS0 bit in ASSR is set), Timer/Counter0
will run during sleep. The device can wake up from either Timer Overflow or Output Compare
event from Timer/Counter0 if the corresponding Timer/Counter0 interrupt enable bits are set in
TIMSK, and the Global Interrupt Enable bit in SREG is set.
If the asynchronous timer is NOT clocked asynchronously, Power-down mode is recommended
instead of Power-save mode because the contents of the registers in the asynchronous timer
should be considered undefined after wake-up in Power-save mode if AS0 is 0.
This sleep mode basically halts all clocks except clkASY, allowing operation only of asynchronous
modules, including Timer/Counter0 if clocked asynchronously.
9.5
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.
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.
47
8160C–AVR–07/09
ATMEL [ ATMEL ]
