11.3.2.1 Enabling and Disabling
The different oscillators can typically be enabled and disabled via both hardware and software mechanisms. Enabling via software is
done by setting the corresponding enable bit in the CMU_OSCENCMD register. Disabling via software is done by setting the
corresponding disable bit in CMU_OSCENCMD. Enabling via hardware can be performed by various peripherals and varies per oscilla-
tor. Disabling via hardware is typically performed on entry of low energy modes. The enable and disable mechanisms for each of the
oscillators are summarized in
Table 11.1 Software Based and Hardware Based Enabling and Disabling of Oscillators on page 285
and
described in more detail below.
Table 11.1. Software Based and Hardware Based Enabling and Disabling of Oscillators
Oscillator
SW Enable
SW Disable
HW Enable
HW Disable
ULFRCO
-
-
Enabled when in
EM0/EM1/EM2/EM3/
EM4H.
EM4S entry depending
on configuration in
EMU_EM4CTRL.
LFRCO
Via LFRCOEN in
CMU_OSCENCMD.
Via LFRCODIS in
CMU_OSCENCMD.
Via WDOGn if it is config-
ured to use LFRCO as its
clock source via the
CLKSEL bitfield in
WDOGn_CTRL while
SWOSCBLOCK is set.
EM3 entry. EM4 entry de-
pending on configuration
in EMU_EM4CTRL.
LFXO
Via LFXOEN in
CMU_OSCENCMD.
Via LFXODIS in
CMU_OSCENCMD.
Via WDOGn if it is config-
ured to use LFXO as its
clock source via the
CLKSEL bitfield in
WDOGn_CTRL while
SWOSCBLOCK is set.
EM3 entry. EM4 entry de-
pending on configuration
in EMU_EM4CTRL.
HFRCO
Via HFRCOEN in
CMU_OSCENCMD.
Via HFRCODIS in
CMU_OSCENCMD.
Reset exit. EM2/EM3 ex-
it. Automatic control by
LEUART RX/TX DMA
wake-up as configured in
LEUARTn_CTRL.
EM2/EM3/EM4 entry. Au-
tomatic control by
LEUART RX/TX DMA
wake-up as configured in
LEUARTn_CTRL. Auto-
matic start and selection
of HFXO causes HFRCO
disable.
AUXHFRCO
Via AUXHFRCOEN in
CMU_OSCENCMD.
Via AUXHFRCODIS in
CMU_OSCENCMD.
Automatic control by
ADC and LESENSE.
EM2/EM3/EM4 entry. Au-
tomatic control by ADC
and LESENSE even in
EM2/EM3.
HFXO
Via HFXOEN in
CMU_OSCENCMD.
Via HFXODIS in
CMU_OSCENCMD.
Automatic start by Radio
Controller (RAC) or
EM0/EM1 entry as con-
figured in
CMU_HFXOCTRL.
EM2/EM3/EM4 entry.
Reference Manual
CMU - Clock Management Unit
silabs.com
| Building a more connected world.
Rev. 1.1 | 285