ATMEGA8_08 Datasheet, PDF (35/308 Pages) ATMEL Corporation – 8-bit with 8K Bytes In-System Programmable Flash

ATmega8(L)
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 6 clock cycles.
Table 14. Active Clock Domains and Wake-up Sources in the Different Sleep Modes
Active Clock Domains
Oscillators
Wake-up Sources
Sleep
Mode
Idle
clk_CPU
clk_FLASH
clk_IO
X
clk_ADC
X
clk_ASY
X
Main Clock
Source Enabled
X
Timer Osc.
Enabled
X⁽²⁾
INT1
INT0
X
TWI
Address
Match
X
Timer
2
X
SPM/
EEPROM
Ready
X
ADC
X
Other
I/O
X
ADC Noise
Reduction
X
X
X
X⁽²⁾
X⁽³⁾
X
X
X
X
Power
Down
X⁽³⁾
X
Power
Save
X⁽²⁾
Standby⁽¹⁾
X
Notes: 1. External Crystal or resonator selected as clock source.
2. If AS2 bit in ASSR is set.
3. Only level interrupt INT1 and INT0.
X⁽²⁾
X⁽³⁾
X
X⁽²⁾
X⁽³⁾
X
Minimizing Power
Consumption
There are several issues to consider when trying to minimize the power consumption in an AVR
controlled system. In general, sleep modes should be used as much as possible, and the sleep
mode should be selected so that as few as possible of the device’s functions are operating. All
functions not needed should be disabled. In particular, the following modules may need special
consideration when trying to achieve the lowest possible power consumption.
Analog-to-Digital
Converter (ADC)
If enabled, the ADC will be enabled in all sleep modes. To save power, the ADC should be dis-
abled before entering any sleep mode. When the ADC is turned off and on again, the next
conversion will be an extended conversion. Refer to “Analog-to-Digital Converter” on page 196
for details on ADC operation.
Analog Comparator
When entering Idle mode, the Analog Comparator should be disabled if not used. When entering
ADC Noise Reduction mode, the Analog Comparator should be disabled. In the other sleep
modes, the Analog Comparator is automatically disabled. However, if the Analog Comparator is
set up to use the Internal Voltage Reference as input, the Analog Comparator should be dis-
abled in all sleep modes. Otherwise, the Internal Voltage Reference will be enabled,
independent of sleep mode. Refer to “Analog Comparator” on page 193 for details on how to
configure the Analog Comparator.
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2486T–AVR–05/08