Freescale Semiconductor MC68HC08KH12 Benutzerhandbuch

MC68HC(7)08KH12

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Rev. 1.1

Advance Information

Freescale Semiconductor

89

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

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.

 shows the structure of the CGM.