Datasheet

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SAM3X / SAM3A [DATASHEET]
Atmel-11057C-ATARM-SAM3X-SAM3A-Datasheet_23-Mar-15
5.5 Active Mode
Active mode is the normal running mode with the core clock running from the fast RC oscillator, the main crystal
oscillator or the PLLA. The power management controller can be used to adapt the frequency and to disable the
peripheral clocks.
5.6 Low Power Modes
The SAM3X/A devices provide the following low-power modes: Backup, Wait, and Sleep.
5.6.1 Backup Mode
The purpose of backup mode is to achieve the lowest power consumption possible in a system which is performing
periodic wake-ups to perform tasks but not requiring fast startup time (< 0.5 ms).
The Supply Controller, zero-power power-on reset, RTT, RTC, backup registers and 32 kHz oscillator (RC or
crystal oscillator selected by software in the Supply Controller) are running. The regulator and the core supply are
off.
Backup mode is based on the Cortex-M3 deep-sleep mode with the voltage regulator disabled.
The SAM3X/A series can be awakened from this mode through the Force Wake-up pin (FWUP), and Wake-up
input pins WKUP0–15, Supply Monitor, RTT or RTC wake-up event. Current consumption is 2.5 µA typical on
VDDBU.
Backup mode can be entered by using the WFE instruction.
The procedure to enter Backup mode using the WFE instruction is the following:
1. Write a 1 to the SLEEPDEEP bit in the Cortex-M3 processor System Control Register (SCR) (refer to
Section 10.21.7 “System Control Register”).
2. Execute the WFE instruction of the processor.
Exit from Backup mode happens if one of the following enable wake-up events occurs:
 Low level, configurable debouncing on FWUP pin
 Level transition, configurable debouncing on pins WKUPEN0–15
 SM alarm
 RTC alarm
 RTT alarm
5.6.2 Wait Mode
The purpose of the wait mode is to achieve very low power consumption while maintaining the whole device in a
powered state for a startup time of less than 10 µs.
In this mode, the clocks of the core, peripherals and memories are stopped. However, the core, peripherals and
memories power supplies are still powered. From this mode, a fast start up is available.
This mode is entered via Wait for Event (WFE) instructions with LPM = 1 (Low Power Mode bit in PMC_FSMR).
The Cortex-M3 is able to handle external events or internal events in order to wake-up the core (WFE). This is
done by configuring the external lines WKUP0–15 as fast startup wake-up pins (refer to Section 5.8 “Fast
Startup”). RTC or RTT Alarm and USB wake-up events can be used to wake up the CPU (exit from WFE).
Current consumption in Wait mode is typically 23 µA for total current consumption if the internal voltage regulator
is used or 15 µA if an external regulator is used.
The procedure to enter Wait mode is the following:
1. Select the 4/8/12 MHz Fast RC Oscillator as Main Clock.
2. Set the LPM bit in the PMC Fast Startup Mode Register (PMC_FSMR).
3. Execute the WFE instruction of the processor.