M68ICS08GR datasheet(100/408 Pages) FREESCALE

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Clock Generator Module (CGMC)

Technical Data

MC68HC908GR8 — Rev 4.0

100

Clock Generator Module (CGMC)

MOTOROLA

7.3 Features

Features of the CGMC include:

•

Phase-locked loop with output frequency in integer multiples of an

integer dividend of the crystal reference

•

Low-frequency crystal operation with low-power operation and

high-output frequency resolution

•

Programmable prescaler for power-of-two increases in frequency

•

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

•

Configuration register bit to allow oscillator operation during stop

mode

7.4 Functional Description

The CGMC 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.

•

Base clock selector circuit — This software-controlled circuit

selects either CGMXCLK divided by two or the VCO clock,

CGMVCLK, divided by two as the base clock, CGMOUT. The SIM

derives the system clocks from either CGMOUT or CGMXCLK.

Figure 7-1 shows the structure of the CGMC.

Freescale Semiconductor, Inc.

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