MC68HC908AZ60 Datasheet, PDF (130/480 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Clock Generator Module (CGM)
Parametric Influences on Reaction Time . . . . . . . . . . . . . . . . . . . 150
Choosing a Filter Capacitor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
Reaction Time Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
Introduction
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 clocks are derived. 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 1-MHz to 16-MHz crystals or ceramic
resonators. The PLL can generate an 8-MHz bus frequency without
using high frequency crystals.
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
• CPU Interrupt on Entry or Exit from Locked Condition
MC68HC908AZ60 — Rev 2.0
128
Clock Generator Module (CGM)
2-cgm
MOTOROLA