Clock Management Unit

CMU - Clock Management Unit

Quick Facts

EFM32 Clock Management

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