Z8F1680SH020SG Datasheet, PDF (346/412 Pages) Zilog, Inc. – High-Performance 8-Bit Microcontrollers

Z8 Encore! XP^® F1680 Series
Product Specification
321
Chapter 25. Crystal Oscillator
The products in the Z8 Encore! XP F1680 Series contain a primary on-chip crystal oscilla-
tor for use with external crystals with 1 MHz to 20 MHz frequencies, plus a secondary 32 K
crystal oscillator. In addition, the external oscillator supports external RC networks with
oscillation frequencies up to 4 MHz. The 32 K secondary crystal oscillator does not feature
an external RC oscillator mode. 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 peripher-
als. Additionally, the secondary 32 K crystal oscillator can only be used to generate a clock
for three timers.
Alternatively, the X_IN and X2_IN input pins can also accept a CMOS-level clock input sig-
nal (for X_IN, the frequency range is 32 kHz–20 MHz; for X2_IN, the range is below 4 MHz).
If an external clock generator is used, the X_OUT or X2_OUT pin must remain unconnected.
The Z8 Encore! XP F1680 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;
the frequency of the signal on the X2_IN determines the frequency of the timers.
Note:
Although the X_IN pin can be used as a primary system clock input for an external clock
generator, the CLKIN pin is better suited for such use. For details, see the System Clock
Selection section on page 315.
25.1. Operating Modes
The primary on-chip crystal oscillator supports three oscillator modes:
• Medium power for use with medium frequency crystals or ceramic resonators (1MHz
to 8 MHz)
• Maximum power for use with high-frequency crystals (8MHz to 20MHz)
• On-chip oscillator configured for use with external RC networks or external clock input
(< 4 MHz)
The primary on-chip crystal oscillator mode is selected using user-programmable Flash
option bits. For information, see the Flash Option Bits section on page 276. The secondary
32 kHz crystal oscillator supports two oscillator modes:
• NORMAL Mode for use with 32kHz crystals
• On-chip oscillator configured for use with external clock input
PS025015-1212
PRELIMINARY
Crystal Oscillator