Freescale Semiconductor MC68HC08KH12 Manuel d'utilisateur Page 89

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MC68HC(7)08KH12Rev. 1.1 Advance Information
Freescale Semiconductor
89
8.3 Features
Features of the CGM include:
VCO Center-Of-Range Frequuency tuned to 48MHz for Low-Jitter
Clock Reference for USB Module
Low-Frequency Crystal Operation with Low-Power Operation and
High-Output Frequency Resolution
Programmable Reference Divider for Even Greater Resolution
Programmable Prescaler for Power-of-Two Increases in Bus
Frequency
Automatic Bandwidth Control Mode for Low-Jitter Operation
Automatic Frequency Lock Detector
CPU Interrupt on Entry or Exit from Locked Condition
8.4 Functional Description
The CGM consists of three major submodules:
Crystal oscillator circuit — The crystal oscillator circuit generates
the constant crystal frequency clock, CGMXCLK.
Phase-locked loop (PLL) — The PLL generates the
programmable VCO frequency clock, CGMVCLK and CGMPCLK.
Base clock selector circuit — This software-controlled circuit
selects either CGMXCLK divided by two or the PLL clock,
CGMPCLK, divided by two as the base clock, CGMOUT. The SIM
derives the system clocks from CGMOUT.
Figure 8-1 shows the structure of the CGM.
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