Rainbow Electronics ATmega8515L - Manual (Page 40)

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ATmega8515(L)
2512A–AVR–04/02
Standby Mode When the SM2..0 bits are written to 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.
Notes: 1. External Crystal or resonator selected as clock source
2. Only INT2 or level interrupt INT1 and INT0
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 possi-
ble, 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 Comparator When entering Idle mode, the Analog Comparator should be disabled if not needed. 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 disabled in all sleep modes. Otherwise, the Internal Volt-
age Reference will be enabled, independent of sleep mode. Refer to “Analog
Comparator” on page 160 for details on how to configure the Analog Comparator.
Brown-out Detector If the Brown-out Detector is not needed in the application, this module should be turned
off. If the Brown-out Detector is enabled by the BODEN Fuse, it will be enabled in all
sleep modes, and hence, always consume power. In the deeper sleep modes, this will
contribute significantly to the total current consumption. Refer to “Brown-out Detection”
on page 45 for details on how to configure the Brown-out Detector.
Internal Voltage Reference The Internal Voltage Reference will be enabled when needed by the Brown-out Detector
or the Analog Comparator. If these modules are disabled as described in the sections
above, the internal voltage reference will be disabled and it will not be consuming
power. When turned on again, the user must allow the reference to start up before the
output is used. If the reference is kept on in sleep mode, the output can be used imme-
diately. Refer to “Internal Voltage Reference” on page 47 for details on the start-up time.
Watchdog Timer If the Watchdog Timer is not needed in the application, this module should be turned off.
If the Watchdog Timer is enabled, it will be enabled in all sleep modes, and hence,
always consume power. In the deeper sleep modes, this will contribute significantly to
the total current consumption. Refer to page 50 for details on how to configure the
Watchdog Timer.
Table 17. Active Clock Domains and Wake-up Sources in the Different Sleep Modes
Active Clock domains Oscillators Wake-up Sources
Sleep Mode clk
CPU
clk
FLASH
clk
IO
Main Clock
Source Enabled
INT2
INT1
INT0 SPM/
EEPROM
Ready Other I/O
Idle X X X X X
Power-down X (2)
Standby (1) X X (2)