M68ICS08GR datasheet(99/408 Pages) FREESCALE

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MC68HC908GR8 — Rev 4.0

Technical Data

MOTOROLA

Clock Generator Module (CGMC)

Technical Data — MC68HC908GR8

Section 7. Clock Generator Module (CGMC)

7.1 Contents

7.2

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

7.3

Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

7.4

Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

7.5

I/O Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

7.6

CGMC Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114

7.7

Interrupts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

7.8

Special Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

7.9

Acquisition/Lock Time Specifications . . . . . . . . . . . . . . . . . . .125

7.2 Introduction

This section describes the clock generator module. The CGMC

generates the crystal clock signal, CGMXCLK, which operates at the

frequency of the crystal. The CGMC also generates the base clock

signal, CGMOUT, which is based on either the crystal clock divided by

two or the phase-locked loop (PLL) clock, CGMVCLK, divided by two. In

user mode, CGMOUT is the clock from which the SIM derives the

system clocks, including the bus clock, which is at a frequency of

CGMOUT/2. In monitor mode, PTC3 determines the bus clock. The PLL

is a fully functional frequency generator designed for use with crystals or

ceramic resonators. The PLL can generate an 8-MHz bus frequency

using a 32-kHz crystal.

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