Chapter 24Multipurpose Clock Generator (MCG)24.1 IntroductionNOTEFor the chip-specific implementation details of this module'sinstances see the chip configuration information.The multipurpose clock generator (MCG) module provides several clock source choicesfor the MCU. The module contains a frequency-locked loop (FLL) and a phase-lockedloop (PLL). The FLL is controllable by either an internal or an external reference clock.The PLL is controllable by the external reference clock. The module can select either ofthe FLL or PLL output clocks, or either of the internal or external reference clocks as asource for the MCU system clock. The MCG operates in conjuction with a crystaloscillator, which allows an external crystal, ceramic resonator, or another external clocksource to produce the external reference clock.24.1.1 FeaturesKey features of the MCG module are:• Frequency-locked loop (FLL):• Digitally-controlled oscillator (DCO)• DCO frequency range is programmable for up to four different frequency ranges.• Option to program and maximize DCO output frequency for a low frequencyexternal reference clock source.• Option to prevent FLL from resetting its current locked frequency whenswitching clock modes if FLL reference frequency is not changed.KL25 Sub-Family Reference Manual, Rev. 3, September 2012Freescale Semiconductor, Inc. 367
