11.3.4 Energy Modes
The availability of oscillators and system clocks depends on the chosen energy mode. Default the high frequency oscillators (HFRCO,
AUXHFRCO, and HFXO) and high frequency clocks (HFSRCLK, HFCLK, HFCORECLK, HFBUSCLK, HFPERCLK, HFRADIOCLK,
HFCLKLE) are available downto EM1 Sleep. From EM2 Deep Sleep onwards these oscillators and clocks are normally off, although
special cases exist as summarized in
Table 11.5 Oscillator and Clock Availability in Energy Modes on page 303
Energy Mode Overview on page 215
. The CMU overview figure in
Figure 11.1 CMU Overview - High Frequency Portion on page 280
and
Figure 11.2 CMU Overview - Low Frequency Portion on page 281
also indicate which oscillators and clocks can be used in what
energy modes.
The low frequency oscillators (LFRCO and LFXO) are available in all energy modes except in EM3 Stop when they are off by definition.
Default these oscillators are also off in EM4 Hibernate and EM4 Shutoff, but they can be retained on in these states as well if needed.
The ultra low frequency oscillator (ULFRCO) is default on in all energy modes, except for EM4 Shutoff, but it can be retained on in that
mode as well if needed. The low frequency clocks (LFACLK, LFBCLK, LFECLK, WDOGnCLK, RFSENSECLK, and CRYOCLK) are in
various power domains and therefore their availability not only depends on the chosen clock source, but also on the chosen energy
mode as indicated in
Table 11.5 Oscillator and Clock Availability in Energy Modes on page 303
Table 11.5. Oscillator and Clock Availability in Energy Modes
EM0 Active/EM1
Sleep
EM2 Deep Sleep
EM3 Stop
EM4 Hibernate
EM4 Shutoff
HFRCO
Off
Off
Off
Off
HFXO
Off
Off
Off
Off
AUXHFRCO
Off
Off
LFRCO, LFXO
Off
ULFRCO
On
On
On
On
HFSRCLK, HFCLK,
HFCORECLK,
HFBUSCLK,
HFPERCLK, HFRA-
DIOCLK, HFCLKLE
Off
Off
Off
Off
AUXCLK
Off
Off
ADCnCLK
Off
Off
LFACLK, LFBCLK
Off
Off
LFECLK
Off
WDOGnCLK
Off
Off
CRYOCLK
1
Under software control.
2
Default off, but kept active if used by the ADC.
3
Default off, but can be retained on.
4
Will be kept on if AUXHFRCO is selected as clock source.
5
On only if ULFRCO is used as clock source.
Reference Manual
CMU - Clock Management Unit
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