Z8F082ASH020SC Datasheet, PDF (187/244 Pages) Zilog, Inc. – Z8 Encore XP-R F08xA Series with eXtended Peripherals

Z8 Encore! XP^® F08xA Series
Product Specification
169
Internal Precision Oscillator
Overview
The Internal Precision Oscillator (IPO) is designed for use without external components.
The user can either manually trim the oscillator for a non-standard frequency or use the
automatic factory-trimmed version to achieve a 5.53MHz frequency. IPO features include:
• On-chip RC oscillator that does not require external components
• Output frequency of either 5.53MHz or 32.8KHz (contains both a fast and a slow mode)
• Trimming possible through Flash option bits with user override
• Elimination of crystals or ceramic resonators in applications where high timing accuracy
is not required.
Operation
The internal oscillator is an RC relaxation oscillator that has had 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, such as capacitors. An 8-bit trimming register, incorpo-
rated into the design, compensates for absolute variation of oscillator frequency. Once
trimmed the oscillator frequency is stable and does not require subsequent calibration.
Trimming was performed during manufacturing and is not necessary for the user to repeat
unless a frequency other than 5.53MHz (fast mode) or 32.8kHz (slow mode) 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 “Trim Bit Address Space” on
page 142.
Select one of two frequencies for the oscillator: 5.53MHz and 32.8KHz, using the OSC-
SEL bits in the “Oscillator Control” on page 160.
PS024705-0405
PRELIMINARY
Internal Precision Oscillator