Clock Management Unit

CMU - Clock Management Unit

Quick Facts

What?

The CMU controls oscillators and clocks. EFM32 supports four different oscillators with minimized power consumption and short start-up time. Two RC oscillators with HW support for calibration ensures high accuracy:

HFRC (7-28MHz) => IHFRC = 20-100 µA

LFRC (32kHz) => ILFRC = < 100 nA

Additionally, a 32 kHz and 4-32 MHz crystal oscillator is available with current consumption of typical 100 nA and less than 200 µA respectively.

Why?

Oscillator and clocks contribute significantly to the power consumption of the MCU. With the low power oscillators combined with the flexible clock control scheme, it is possible to minimize the energy consumption in any given application.

How?

The CMU can configure different clock sources, enable/disable clocks to peripherals on an individual basis and set-up prescaling to the different clock domains. The short oscillator start-up times make duty cycling between active mode and the different low energy modes painless.

Features

The Clock Management Unit (CMU) is responsible for controlling the oscillators and clocks on-board the EFM32. The CMU provides the capability to turn on and off the clock on an individual basis to all peripheral modules in addition to enable/disable the available oscillators. The CMU provides the necessary flexibility such that the SW can minimize the energy consumption in any specific application by not wasting power on peripherals and modules that are inactive.

Multiple clock sources available (integratedRC and Crystal Oscillators)
Current starved oscillators ensures low energy operation
Low start-up times
Dynamic system clock division
Clock prescaler selection for 32 kHz peripheral modules
Clock Gating

A digital clock output is available on an output pin, selectable from different clock sources