Freescale Semiconductor MC68HC08KH12 manual 1shows the structure of the CGM

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

8.4Functional Description

The CGM consists of three major submodules:

•Crystal oscillator circuit — The crystal osc illator circuit generates the constant crystal frequency clock, CGMXCLK.

•Phase-locked loop (PLL) — The P LL generates the programmable VCO frequency clock, CGMVCLK and CGMPCLK.

•Base clock selector circuit — Th is 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 8-1shows the structure of the CGM.

MC68HC(7)08KH12 — Rev. 1.1	Advance Information
Freescale Semiconductor	89