Z8F042ASJ020EG2156 Datasheet, PDF (213/280 Pages) Zilog, Inc. – High-Performance 8-Bit Microcontrollers

Z8 Encore! XP^® F082A Series
Product Specification
198
Crystal Oscillator
The products in the Z8 Encore! XP F082A Series contain an on-chip crystal oscillator for
use with external crystals with 32 kHz to 20 MHz frequencies. In addition, the oscillator
supports external RC networks with oscillation frequencies up to 4 MHz or ceramic reso-
nators with frequencies up to 8 MHz. 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 X_IN input pin can also accept a CMOS-level clock input signal
(32 kHz–20 MHz). If an external clock generator is used, the X_OUT pin must be left uncon-
nected. The Z8 Encore! XP F082A Series products do not contain an internal clock
divider. The frequency of the signal on the X_IN input pin determines the frequency of the
system clock.
Note: Although the X_IN pin can be used as an input for an external clock generator, the CLKIN
pin is better suited for such use (see the System Clock Selection section on page 193).
Operating Modes
The Z8 Encore! XP F082A Series products support four oscillator modes:
• Minimum power for use with very low frequency crystals (32kHz–1MHz)
• Medium power for use with medium frequency crystals or ceramic resonators (0.5MHz
to 8 MHz)
• Maximum power for use with high frequency crystals (8MHz to 20MHz)
• On-chip oscillator configured for use with external RC networks (<4MHz)
The oscillator mode is selected via user-programmable Flash option bits. See the Flash
Option Bits chapter on page 159 for information.
Crystal Oscillator Operation
The XTLDIS Flash option bit 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 Reg-
ister, 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.
PS022828-0413
PRELIMINARY
Crystal Oscillator