MC68HC908MR8 Datasheet, PDF (112/372 Pages) Motorola, Inc – Microcontrollers

Clock Generator Module (CGM)
8.11.3 Choosing a Filter Capacitor . . . . . . . . . . . . . . . . . . . . . .136
8.11.4 Reaction Time Calculation . . . . . . . . . . . . . . . . . . . . . . .137
8.2 Introduction
This section describes the clock generator module (CGM, version A).
The CGM generates the crystal clock signal, CGMXCLK, which operates
at the frequency of the crystal. The CGM also generates the base clock
signal, CGMOUT, from which the system integration module (SIM)
derives the system clocks.
CGMOUT is based on either the crystal clock divided by two or the
phase-locked loop (PLL) clock, CGMVCLK, divided by two. The PLL is
a frequency generator designed for use with crystals or ceramic
resonators. The PLL can generate an 8-MHz bus frequency without
using a 32-MHz crystal.
8.3 Features
Features of the CGM include:
• Phase-locked loop with output frequency in integer multiples of the
crystal reference
• Programmable hardware voltage-controlled oscillator (VCO) for
low-jitter operation
• Automatic bandwidth control mode for low-jitter operation
• Automatic frequency lock detector
• Central processor unit (CPU) interrupt on entry or exit from locked
condition
Technical Data
112
Clock Generator Module (CGM)
MC68HC908MR8 — Rev 4.1
Freescale Semiconductor