ATmega64A datasheet(47/392 Pages) ATMEL

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8160C–AVR–07/09

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 clk

ASY, allowing operation only of asynchronous

modules, including Timer/Counter0 if clocked asynchronously.

9.5

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.

9.6

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.

ATmega64A Datasheet(PDF) 47 Page - ATMEL Corporation

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