
Advance Information
MC68HC908AS60
156
Clock Generator Module (CGM)
MOTOROLA
Clock Generator Module (CGM)
10.2 Introduction
The clock generator module (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 8-MHz
crystals or ceramic resonators. The PLL can generate an 8-MHz bus
frequency without using a 32-MHz crystal.
10.3 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
CPU interrupt on entry or exit from locked condition