11.3.1.9 LFECLK - Low Frequency E Clock
LFECLK is the selected clock for the Low Energy E Peripherals. There are several selectable sources for LFECLK: LFRCO, LFXO and
ULFRCO. In addition, the LFECLK can be disabled, which is the default setting. The selection is configured using the LFE field in
CMU_LFECLKSEL.
The bus interface to the Low Energy E Peripherals is clocked by HFBUSCLK
LE
and this clock therefore needs to be enabled when
programming a LE peripheral.
Note:
LFECLK is in a different power domain than LFACLK and LFBCLK, which makes it available all the way down to EM4 Hibernate.
Each Low Energy Peripheral that is clocked by LFECLK has its own prescaler setting and enable bit. The prescaler settings are config-
ured using CMU_LFEPRESC0 and the clock enable bits can be found in CMU_LFECLKEN0.
11.3.1.10 PCNTnCLK - Pulse Counter N Clock
Each available pulse counter is driven by its own clock, PCNTnCLK where n is the pulse counter instance number. Each pulse counter
can be configured to use an external pin (PCNTn_S0) or LFACLK as PCNTnCLK.
11.3.1.11 WDOGnCLK - Watchdog Timer Clock
The Watchdog Timer (WDOGn) can be configured to use one of many different clock sources. Refer to CLKSEL field in WDOGn_CTRL
for a complete list.
11.3.1.12 CRYOCLK - Cryotimer Clock
The Cryotimer clock can be configured to use one of many different clock sources. Refer to OSCSEL field in CRYOTIMER_CTRL for a
complete list. The Cryotimer can also run in EM4 Hibernate/Shutoff provided that its selected clock is kept enabled as configured in
EMU_EM4CTRL.
11.3.1.13 RFSENSECLK - RFSENSE Clock
The RFSENSE clock can be configured to use one of four different clock sources: LFRCO, LFXO, ULFRCO or the RF Detector Clock.
The RFSENSE module can also run in EM4 Hibernate/Shutoff provided that its selected clock is kept enabled as configured in
EMU_EM4CTRL.
11.3.1.14 AUXCLK - Auxiliary Clock
AUXCLK is a 1 MHz - 38 MHz clock driven by a separate RC oscillator, the AUXHFRCO. This clock can be used for ADC operation,
LESENSE operation and Serial Wire Output (SWO). When the AUXHFRCO is selected as the ADCn clock via the ADCnCLKSEL bit-
field in the CMU_ADCCTRL register, or if needed by LESENSE, this clock will become active automatically when needed. Even if the
AUXHFRCO has not been enabled explicitly by software, the ADC or LESENSE can automatically start and stop it. The AUXHFRCO is
explicitly enabled by writing a 1 to AUXHFRCOEN in CMU_OSCENCMD. This explicit enabling is required when selecting the AUXCLK
for SWO operation.
11.3.1.15 Debug Trace Clock
The CMU selects the clock used for debug trace via the DBGCLKSEL register. The user can useAUXHFRCO or the HFCLK. The selec-
ted debug trace clock will be used to run the Cortex-M4 trace logic.
Note:
When using AUXHFRCO as the debug trace clock, it must be stopped before entering EM2 or EM3.
11.3.2 Oscillators
Reference Manual
CMU - Clock Management Unit
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