...the world's most energy friendly microcontrollers
2014-07-02 - Gecko Family - d0001_Rev1.30
95
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11 CMU - Clock Management Unit
0 1 2 3
4
Oscillat ors
CMU
WDOG clock
LETIMER clock
LCD clock
Peripheral A clock
Peripheral B clock
Peripheral C clock
Peripheral D clock
CPU clock
Quick Facts
What?
The CMU controls oscillators and clocks.
EFM32G supports five different oscillators
with minimized power consumption and short
start-up time. An additional separate RC
oscillator is used for flash programming and
debug trace. The CMU also has HW support
for calibration of RC oscillators.
Why?
Oscillators 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 the prescaler
for the different clocks. The short oscillator
start-up times makes duty-cycling between
active mode and the different low energy
modes (EM2-EM4) very efficient. The
calibration feature ensures high accuracy RC
oscillators. Several interrupts are available to
avoid CPU polling of flags.
11.1 Introduction
The Clock Management Unit (CMU) is responsible for controlling the oscillators and clocks on-board
the EFM32G. 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 and configure the available oscillators. The high degree
of flexibility enables software to minimize energy consumption in any specific application by not wasting
power on peripherals and oscillators that are inactive.
11.2 Features
• Multiple clock sources available:
• 1-28 MHz High Frequency RC Oscillator (HFRCO)
• 4-32 MHz High Frequency Crystal Oscillator (HFXO)
• 32.768 Hz Low Frequency RC Oscillator (LFRCO)
• 32.768 Hz Low Frequency Crystal Oscillator (LFXO)
• 1 kHz Ultra Low Frequency RC Oscillator (ULFRCO)
• Low power oscillators
• Low start-up times
• Separate prescaler for High Frequency Core Clocks (HFCORECLK) and Peripheral Clocks
(HFPERCLK)
• Individual clock prescaler selection for each Low Energy Peripheral
Summary of Contents for EFM32G
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