Atmel XMEGA-A1 Xplained Evaluation Board ATAVRXPLAIN ATAVRXPLAIN Data Sheet
Product codes
ATAVRXPLAIN
AVR1010
5
8267B-AVR-12/10
Minimize power consumption by switching clock sources rather than relying on
prescaling alone for reducing clock rates.
prescaling alone for reducing clock rates.
2.6 Wake-Up Delays
When the device wakes up from sleep modes deeper than IDLE (with the exception
of the two STANDBY-modes), the system clock source must stabilize before the CPU
starts to operate. This introduces a short delay which depends on the selected clock
source. If an internal RC oscillator or external clock is used, the start-up delay is 6
cycles. This is in addition to the RC oscillator start-up time. If the XTAL oscillator is
used, the start-up delay is configurable. If frequency stability is wanted, it is
recommended with start-up delays of 1,000 cycles for ceramic resonators and
16,000cycles for quartz crystals respectively. This is in addition to the oscillator start-
up time, which will depend on the resonator and load capacitances.
of the two STANDBY-modes), the system clock source must stabilize before the CPU
starts to operate. This introduces a short delay which depends on the selected clock
source. If an internal RC oscillator or external clock is used, the start-up delay is 6
cycles. This is in addition to the RC oscillator start-up time. If the XTAL oscillator is
used, the start-up delay is configurable. If frequency stability is wanted, it is
recommended with start-up delays of 1,000 cycles for ceramic resonators and
16,000cycles for quartz crystals respectively. This is in addition to the oscillator start-
up time, which will depend on the resonator and load capacitances.
In addition, there is a 13 cycle minimum delay before an Interrupt Service Routine
(ISR) starts executing after wake-up. This is due to, e.g. the program counter being
pushed on stack and the jump to the ISR.
(ISR) starts executing after wake-up. This is due to, e.g. the program counter being
pushed on stack and the jump to the ISR.
During the start-up delay the power consumption is close to the power consumption in
IDLE, and thus represents “inefficient” power. If possible, it is therefore recommended
to wake up as seldom as possible and rather “do more” every time the device wakes
up.
IDLE, and thus represents “inefficient” power. If possible, it is therefore recommended
to wake up as seldom as possible and rather “do more” every time the device wakes
up.
To minimize the wake-up delay and conserve power, use an RC oscillator or external
clock source, and wake up as seldom as possible.
clock source, and wake up as seldom as possible.
2.7 Power Reduction Registers
Most peripherals and internal modules can be individually stopped to avoid that these
draw power in ACTIVE mode and in IDLE sleep. This is done by setting their
respective bits in the Power Reduction Registers (PRR), which causes them to be
disconnected from the peripheral clock domain. It is required to disable modules and
peripherals via their respective control registers before setting their PRR bit, for the
Power Reduction to be effective. Some modules must be reinitialized after clearing
their PRR bit. Please refer to the sections about the individual PRR-bits in the
datasheet manual for more information.
draw power in ACTIVE mode and in IDLE sleep. This is done by setting their
respective bits in the Power Reduction Registers (PRR), which causes them to be
disconnected from the peripheral clock domain. It is required to disable modules and
peripherals via their respective control registers before setting their PRR bit, for the
Power Reduction to be effective. Some modules must be reinitialized after clearing
their PRR bit. Please refer to the sections about the individual PRR-bits in the
datasheet manual for more information.
In POWER-SAVE and POWER-DOWN the modules are stopped regardless of the
PRRs, since the peripheral clock domain is disabled.
PRRs, since the peripheral clock domain is disabled.
To minimize power consumption, use the PRRs to disable peripherals and modules
that are not used.
that are not used.
2.8 RTC Clock Source
One of the reasons for using IDLE, POWER-SAVE and EXTENDED STANDBY is
that the RTC and its clock are active in these sleep modes. The RTC is commonly
used to wake the device up at timed intervals.
that the RTC and its clock are active in these sleep modes. The RTC is commonly
used to wake the device up at timed intervals.
For most Atmel
®
AVR
®
XMEGA-families, three different oscillators can be used to
clock the RTC: An external 32kHz crystal, the internal 32kHz RC oscillator and the
internal 32kHz Ultra Low Power (ULP) oscillator. In all cases, a prescaled 1kHz clock
signal is available and should be used for reduced power consumption. For the
external 32kHz crystal oscillator, a special low power mode is also available
(X32KLPM).
internal 32kHz Ultra Low Power (ULP) oscillator. In all cases, a prescaled 1kHz clock
signal is available and should be used for reduced power consumption. For the
external 32kHz crystal oscillator, a special low power mode is also available
(X32KLPM).