56F8322 datasheet(28/136 Pages) FREESCALE

28 / 136 page

56F8322 Techncial Data, Rev. 16

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.

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 3-1. 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.

Figure 3-1 Connecting to a Crystal Oscillator

Note:

The OCCS_COHL bit should be set to 1 when a crystal oscillator is used. The reset condition on the

OCCS_COHL bit is 0. Please see the COHL bit in the Oscillator Control (OSCTL) register, discussed

in the 56F8300 Peripheral User Manual.

Sample External Crystal Parameters:

Rz = 750 KΩ

Note: If the operating temperature range is limited to

below 85oC (105oC junction), then Rz = 10 Meg Ω

CLKMODE = 0

EXTAL XTAL

CL1

CL2

Crystal Frequency = 4 - 8MHz (optimized for 8MHz)

EXTAL XTAL

56F8322 bảng dữ liệu(PDF) 28 Page - Freescale Semiconductor, Inc