EFM32WG Datasheet, PDF (128/834 Pages) List of Unclassifed Manufacturers – The EFM32WG Wonder Gecko is the ideal choice for demanding 8-, 16-, and 32-bit energy sensitive applications.

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Each Low Energy Peripheral that is clocked by LFACLK has its own prescaler setting and enable bit.
The prescaler settings are configured using CMU_LFAPRESC0 and the clock enable bits can be found
in CMU_LFACLKEN0. Notice that the LCD has an additional high resolution prescaler for Frame Rate
Control, configured by FDIV in CMU_LCDCTRL. When operating in oversampling mode, the pulse
counters are clocked by LFACLK. This is configured for each pulse counter (n) individually by setting
PCNTnCLKSEL in CMU_PCNTCTRL.
11.3.1.5 LFBCLK - Low Frequency B Clock
LFBCLK is the selected clock for the Low Energy B Peripherals. There are four selectable sources for
LFBCLK: LFRCO, LFXO, HFCORECLK/2 and ULFRCO. In addition, the LFBCLK can be disabled. From
reset, the LFBCLK source is set to LFRCO. However, note that the LFRCO is disabled from reset. The
selection is configured using the LFB field in CMU_LFCLKSEL. The HFCORECLK/2 setting allows the
Low Energy B Peripherals to be used as high-frequency peripherals.
Note
If HFCORECLK/2 is selected as LFBCLK, the clock will stop in EM2/3.
Each Low Energy Peripheral that is clocked by LFBCLK has its own prescaler setting and enable bit.
The prescaler settings are configured using CMU_LFBPRESC0 and the clock enable bits can be found
in CMU_LFBCLKEN0.
11.3.1.6 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.
11.3.1.7 WDOGCLK - Watchdog Timer Clock
The Watchdog Timer (WDOG) can be configured to use one of three different clock sources: LFRCO,
LFXO or ULFRCO. ULFRCO (Ultra Low Frequency RC Oscillator) is a separate 1 kHz RC oscillator
that also runs in EM3.
11.3.1.8 AUXCLK - Auxiliary Clock
AUXCLK is a 1-28 MHz clock driven by a separate RC oscillator, AUXHFRCO. This clock is used for
flash programming, and Serial Wire Output (SWO), and LESENSE operation. During flash programming,
or if needed by LESENSE, this clock will be active. If the AUXHFRCO has not been enabled explicitly by
software, the MSC or LESENSE module will automatically start and stop it. The AUXHFRCO is enabled
by writing a 1 to AUXHFRCOEN in CMU_OSCENCMD. This explicit enabling is required when SWO
is used.
11.3.2 Oscillator Selection
11.3.2.1 Start-up Time
The different oscillators have different start-up times. For the RC oscillators, the start-up time is fixed,
but both the LFXO and the HFXO have configurable start-up time. At the end of the start-up time a ready
flag is set to indicated that the start-up time has exceeded and that the clock is available. The low start-
up time values can be used for an external clock source of already high quality, while the higher start-up
times should be used when the clock signal is coming directly from a crystal. The startup time for HFXO
and LFXO can be set by configuring the HFXOTIMEOUT and LFXOTIMEOUT bitfields, respectively.
Both bitfields are located in CMU_CTRL. For HFXO it is also possible to enable a glitch detection filter
by setting HFXOGLITCHDETEN in CMU_CTRL. The glitch detector will reset the start-up counter if a
glitch is detected, making the start-up process start over again.
2013-05-08 - Wonder Gecko Family - d0233_Rev0.50
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