Freescale Semiconductor MC68HC08KH12 - Manual (Page 89)

MC68HC(7)08KH12 — Rev. 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.