Freescale Semiconductor HCS08 Series, Reference Manual

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MC9S08JS16 MCU Series Reference Manual, Rev. 4
Freescale Semiconductor 115
Chapter 9
Multi-Purpose Clock Generator (S08MCGV1)
9.1 Introduction
The multi-purpose clock generator (MCG) module provides several clock source choices for the MCU.
The module contains a frequency-locked loop (FLL) and a phase-locked loop (PLL) that are controllable
by an internal or an external reference clock. The module can select either of the FLL or PLL clocks, and
either of the internal or external reference clocks as a source for the MCU system clock. Whichever clock
source is chosen, it is passed through a reduced bus divider which allows a lower output clock frequency
to be derived. The MCG also controls an external oscillator (XOSC) for the use of a crystal or resonator
as the external reference clock.
For USB operation on the MC9S08JS16 series, the MCG must be configured for PLL engaged external
(PEE) mode using a crystal to achieve an MCGOUT frequency of 48 MHz.