EFM32PG22 Gecko MCU Family Data Sheet
System Overview
3.3 Clocking
3.3.1 Clock Management Unit (CMU)
The Clock Management Unit controls oscillators and clocks in the EFM32PG22. Individual enabling and disabling of clocks to all periph-
eral modules is performed by the CMU. The CMU also controls enabling and configuration of the oscillators. A high degree of flexibility
allows software to optimize energy consumption in any specific application by minimizing power dissipation in unused peripherals and
oscillators.
3.3.2 Internal and External Oscillators
The EFM32PG22 supports two crystal oscillators and fully integrates four RC oscillators, listed below.
• A high frequency crystal oscillator (HFXO) with integrated load capacitors, tunable in small steps, provides a precise timing refer-
ence for the MCU. The HFXO can also support an external clock source such as a TCXO for applications that require an extremely
accurate clock frequency over temperature.
• A 32.768 kHz crystal oscillator (LFXO) provides an accurate timing reference for low energy modes.
• An integrated high frequency RC oscillator (HFRCO) is available for the MCU system, when crystal accuracy is not required. The
HFRCO employs fast start-up at minimal energy consumption combined with a wide frequency range, from 1 MHz to 76.8 MHz.
• An integrated fast start-up RC oscillator (FSRCO) that runs at a fixed 20 MHz
• An integrated low frequency 32.768 kHz RC oscillator (LFRCO) for low power operation without an external crystal. Precision mode
enables periodic recalibration against the 38.4 MHz HFXO crystal to improve accuracy to +/- 500 ppm.
• An integrated ultra-low frequency 1 kHz RC oscillator (ULFRCO) is available to provide a timing reference at the lowest energy con-
sumption in low energy modes.
3.4 Counters/Timers and PWM
3.4.1 Timer/Counter (TIMER)
TIMER peripherals keep track of timing, count events, generate PWM outputs and trigger timed actions in other peripherals through the
Peripheral Reflex System (PRS). The core of each TIMER is a 16-bit or 32-bit counter with up to 3 compare/capture channels. Each
channel is configurable in one of three modes. In capture mode, the counter state is stored in a buffer at a selected input event. In
compare mode, the channel output reflects the comparison of the counter to a programmed threshold value. In PWM mode, the TIMER
supports generation of pulse-width modulation (PWM) outputs of arbitrary waveforms defined by the sequence of values written to the
compare registers. In addition some timers offer dead-time insertion.
See 3.12 Configuration Summary for information on the feature set of each timer.
3.4.2 Low Energy Timer (LETIMER)
The unique LETIMER is a 24-bit timer that is available in energy mode EM0 Active, EM1 Sleep, EM2 Deep Sleep, and EM3 Stop. This
allows it to be used for timing and output generation when most of the device is powered down, allowing simple tasks to be performed
while the power consumption of the system is kept at an absolute minimum. The LETIMER can be used to output a variety of wave-
forms with minimal software intervention. The LETIMER is connected to the Peripheral Reflex System (PRS), and can be configured to
start counting on compare matches from other peripherals such as the Real Time Clock.
3.4.3 Real Time Clock with Capture (RTCC)
The Real Time Clock with Capture (RTCC) is a 32-bit counter providing timekeeping down to EM3. The RTCC can be clocked by any of
the on-board low-frequency oscillators, and it is capable of providing system wake-up at user defined intervals.
3.4.4 Back-Up Real Time Counter (BURTC)
The Back-Up Real Time Counter (BURTC) is a 32-bit counter providing timekeeping in all energy modes, including EM4. The BURTC
can be clocked by any of the on-board low-frequency oscillators, and it is capable of providing system wake-up at user-defined inter-
vals.
3.4.5 Watchdog Timer (WDOG)
The watchdog timer can act both as an independent watchdog or as a watchdog synchronous with the CPU clock. It has windowed
monitoring capabilities, and can generate a reset or different interrupts depending on the failure mode of the system. The watchdog can
also monitor autonomous systems driven by the Peripheral Reflex System (PRS).
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