Z8F021ASH020SC datasheet(204/276 Pages) ZILOG

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PS022815-0206

Crystal Oscillator

Z8 Encore! XP® 4K Series

Product Specification

185

Crystal Oscillator

Overview

The products in the Z8 Encore! XP® 4K Series contain an on-chip crystal oscillator for use

with external crystals with 32 KHz to 20 MHz frequencies. In addition, the oscillator sup-

ports external RC networks with oscillation frequencies up to 4 MHz or ceramic resona-

tors with frequencies up to 8MHz. The on-chip crystal oscillator can be used to generate

the primary system clock for the internal eZ8 CPU and the majority of the on-chip periph-

erals. Alternatively, the XIN input pin can also accept a CMOS-level clock input signal (32

KHz–20 MHz). If an external clock generator is used, the XOUT pin must be left uncon-

nected. The Z8 Encore! XP® 4K Series products do not contain an internal clock divider.

The frequency of the signal on the XIN input pin determines the frequency of the system

clock.

Although the XIN pin can be used as an input for an external clock generator, the CLKIN

pin is better suited for such use (See System Clock Selection on page 180.)

Operating Modes

The Z8 Encore! XP® 4K Series products support four oscillator modes:

• Minimum power for use with very low frequency crystals (32 KHz–1 MHz)

• Medium power for use with medium frequency crystals or ceramic resonators

(0.5 MHz to 8 MHz)

• Maximum power for use with high frequency crystals (8 MHz to 20 MHz)

• On-chip oscillator configured for use with external RC networks (<4 MHz)

The oscillator mode is selected using user-programmable Flash Option Bits. Please refer

to the chapter Flash Option Bits on page 148 for information.

Crystal Oscillator Operation

The Flash Option bit XTLDIS controls whether the crystal oscillator is enabled during

reset. The crystal may later be disabled after reset if a new oscillator has been selected as

the system clock. If the crystal is manually enabled after reset through the OSCCTL regis-

ter, the user code must wait at least 1000 crystal oscillator cycles for the crystal to stabi-

lize. After this, the crystal oscillator may be selected as the system clock.

Note:

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