56F8335 datasheet(32/160 Pages) FREESCALE

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56F8335 Technical Data, Rev. 1

Freescale Semiconductor

Preliminary

Part 3 On-Chip Clock Synthesis (OCCS)

3.1 Introduction

Refer to the OCCS chapter of the 56F8300 Peripheral User Manual for a full description of the OCCS.

The material contained here identifies the specific features of the OCCS design. Figure 3-1 shows the

specific OCCS block diagram to reference in the OCCS chapter of the 56F8300 Peripheral User Manual.

Figure 3-1 OCCS Block Diagram

3.2 External Clock Operation

The system clock can be derived from an external crystal, ceramic resonator, or an external system clock

signal. To generate a reference frequency using the internal oscillator, a reference crystal or ceramic

resonator must be connected between the EXTAL and XTAL pins.

3.2.1

Crystal Oscillator

The internal oscillator is designed to interface with a parallel-resonant crystal resonator in the frequency

range specified for the external crystal in Table 10-15. A recommended crystal oscillator circuit is shown

in Figure 3-2. Follow the crystal supplier’s recommendations when selecting a crystal, since crystal

parameters determine the component values required to provide maximum stability and reliable start-up.

The crystal and associated components should be mounted as near as possible to the EXTAL and XTAL

pins to minimize output distortion and start-up stabilization time.

EXTAL

XTAL

LCK

Prescaler CLK

Postscaler CLK

FOUT/2

Crystal

OSC

Loss of

Reference

Clock

Detector

Lock

Detector

ZSRC

Bus Interface & Control

FOUT

PLLDB

PLLCOD

PLLCID

Bus

Interface

Loss of Reference

Clock Interrupt

SYS_CLK2

Source to SIM

CLKMODE

÷2

Prescaler

÷ (1,2,4,8)

Postscaler

÷ (1,2,4,8)

PLL

x (1 to 128)

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