Atmel SAM4L Xplained Pro Starter Kit Atmel ATSAM4L-XSTK ATSAM4L-XSTK Data Sheet

42023ES–SAM–07/2013

The BACKUP mode allows achieving the lowest power consumption possible in a system which
is performing periodic wake-ups to perform tasks but not requiring fast startup time.

The Core domain is powered-off. The internal SRAM and register contents of the Core domain
are lost. The Backup domain is kept powered-on. The 32kHz clock (RC32K or OSC32K) is kept
running if enabled to feed modules that require clocking.

In BACKUP mode, the configuration of the I/O lines is preserved. Refer to 

 to have more details.

The Backup mode is entered by using the WFI instruction with the following settings:

• set the SCR.SLEEPDEEP bit to 1. (See the Power Management section in the ARM Cortex-

M4 Processor chapter).

• set the BPM.PSAVE.BKUP bit to 1.

Exit from BACKUP mode happens if a reset occurs or if an enabled wake up event occurs.

The reset sources are:

• BOD33 reset

• BOD18 reset

• WDT reset

• External reset in RESET_N pin

The wake up sources are:

• EIC lines (level transition only)

• BOD33 interrupt

• BOD18 interrupt

• AST alarm, periodic, overflow

• WDT interrupt

The RC32K or OSC32K should be used as clock source for modules if required. The
PMCON.CK32S is used to select one of these two 32kHz clock sources.

Exiting the BACKUP mode is triggered by:

• a reset source: an internal reset sequence is performed according to the reset source. Once 

VDDCORE

 

is stable and has the correct value according to RUN0 mode, the internal reset is 

released and program execution starts. The corresponding reset source is flagged in the 
Reset Cause register (RCAUSE) of the PM.

• a wake up source: the Backup domain is not reset. An internal reset is generated to the Core 

domain, and the system switches back to the previous RUN mode. Once VDDCORE

 

is stable 

and has the correct value, the internal reset in the Core domain is released and program 
execution starts. The BKUP bit is set in the Reset Cause register (RCAUSE) of the PM. It 
allows the user to discriminate between the reset cause and a wake up cause from the 
BACKUP mode. The wake up cause can be found in the Backup Wake up Cause register 
(BPM.BKUPWCAUSE).