Z8F1680SH020SG Datasheet, PDF (352/412 Pages) Zilog, Inc. – High-Performance 8-Bit Microcontrollers

Z8 Encore! XP^® F1680 Series
Product Specification
327
Chapter 26. Internal Precision Oscillator
The Internal Precision Oscillator (IPO) is designed for use without external components.
You can either manually trim the oscillator for a nonstandard frequency or use the auto-
matic factory-trimmed version to achieve a 0.0432–11.0592 MHz frequency. IPO features
include:
• On-chip RC oscillator that does not require external components
• Selectable output frequencies: 11.0592MHz, 5.5296MHz, 2.7648MHz, 1.3824MHz,
0.6912 MHz, 0.3456 MHz, 0.0864 MHz and 0.0432 MHz.
• Trimming possible through Flash-option bits with user override
• Elimination of crystals or ceramic resonators in applications where high timing accu-
racy is not required
• Accuracy: ± 4% over temperature and voltage
26.1. Operation
The internal oscillator is an RC relaxation oscillator that has its sensitivity to power supply
variation minimized. By using ratio tracking thresholds, the effect of power supply voltage
is cancelled out. The dominant source of oscillator error is the absolute variance of chip
level fabricated components, like capacitors. An 8-bit trimming register incorporated into
the design compensates for absolute variation of oscillator frequency. After it is trimmed,
the oscillator frequency is stable and does not require subsequent calibration. Trimming is
performed during manufacturing and is not necessary for you to repeat unless a frequency
other than one of the selectable frequencies is required. Power down this block for
minimum system power.
By default, the oscillator is configured through the Flash Option bits. However, the user
code can override these trim values as described in the Trim Bit Address Space section on
page 282.
Select one of the frequencies for the oscillator using the INTSEL bits in the the Oscillator
Control1 Register section on page 320.
PS025015-1212
PRELIMINARY
Internal Precision Oscillator