Z8F1680SH020SG Datasheet, PDF (340/412 Pages) Zilog, Inc. – High-Performance 8-Bit Microcontrollers

Z8 Encore! XP^® F1680 Series
Product Specification
315
Chapter 24. Oscillator Control
The Z8 Encore! XP F1680 Series devices use five possible clocking schemes, each user-
selectable:
• On-chip precision trimmed RC oscillator
• On-chip oscillator using off-chip crystal or resonator
• On-chip oscillator using external RC network
• External clock drive
• On-chip low-precision Watchdog Timer oscillator
In addition, Z8 Encore! XP F1680 Series devices contain:
• A clock failure detection and recovery circuitry allowing continued operation despite a
failure of the primary oscillator
• A peripheral clock that allows timers to be clocked directly from an external 32kHz
watch crystal
24.1. Operation
This chapter discusses the logic used to select the system clock and handle primary
oscillator failures. Descriptions of the specific operations of each oscillator are outlined
elsewhere in this document. A detailed description of the Watchdog Timer oscillator starts
on page 140, the Internal Precision Oscillator description starts on page 327 and the
chapter outlining the Crystal Oscillator begins on page 321.
24.1.1. System Clock Selection
The oscillator control block is selected from the available clocks. Table 168 details each
clock source and its usage.
PS025015-1212
PRELIMINARY
Oscillator Control