Data Sheet

894
Atmel | SMART SAM D21 [DATASHEET]
Atmel-42181G–SAM-D21_Datasheet–09/2015
33.7.4 Sleep Mode Operation
The Run in Standby bit in the Control A register (CTRLA.RUNSTDBY) controls the behavior of the AC during standby
sleep mode. When the bit is zero, the comparator pair is disabled during sleep, but maintains its current configuration.
When the bit is one, the comparator pair continues to operate during sleep. Note that when RUNSTDBY is zero, the
analog blocks are powered off for the lowest power consumption. This necessitates a start-up time delay when the
system returns from sleep.
When RUNSTDBY is one, any enabled AC interrupt source can wake up the CPU. While the CPU is sleeping, single-
shot comparisons are only triggerable by events. The AC can also be used during sleep modes where the clock used by
the AC is disabled, provided that the AC is still powered (not in shutdown). In this case, the behavior is slightly different
and depends on the measurement mode, as listed in Table 33-1.
Table 33-1. Sleep Mode Operation
33.7.4.1 Continuous Measurement during Sleep
When a comparator is enabled in continuous measurement mode and GCLK_AC_DIG is disabled during sleep, the
comparator will remain continuously enabled and will function asynchronously. The current state of the comparator is
asynchronously monitored for changes. If an edge matching the interrupt condition is found, GCLK_AC_DIG is started to
register the interrupt condition and generate events. If the interrupt is enabled in the Interrupt Enable registers
(INTENCLR/SET), the AC can wake up the device; otherwise GCLK_AC_DIG is disabled until the next edge detection.
Filtering is not possible with this configuration.
Figure 33-9. Continuous Mode SleepWalking
33.7.4.2 Single-Shot Measurement during Sleep
For low-power operation, event-triggered measurements can be performed during sleep modes. When the event occurs,
the Power Manager will start GCLK_AC_DIG. The comparator is enabled, and after the start-up time has passed, a
comparison is done, with filtering if desired, and the appropriate peripheral events and interrupts are also generated, as
shown in Figure 33-10 The comparator and GCLK_AC_DIG are then disabled again automatically, unless configured to
wake the system from sleep. Filtering is allowed with this configuration.
Figure 33-10.Single-Shot SleepWalking
COMPCTRLx.MODE RUNSTDBY=0 RUNSTDBY=1
0 (Continuous) COMPx disabled GCLK_AC_DIG stopped, COMPx enabled
1 (Single-shot) COMPx disabled
GCLK_AC_DIG stopped, COMPx enabled only
when triggered by an input event
GCLK_AC
Comparator
Output or Event
Comparator State
GCLK_AC
Comparator
Output or Event
Input Event
t
STARTUP
t
STARTUP