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| Z8F042ASJ020EG2156 Datasheet, PDF (216/280 Pages) Zilog, Inc. – High-Performance 8-Bit Microcontrollers | |||
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Z8 Encore! XP® F082A Series
Product Specification
201
Oscillator Operation with an External RC Network
Figure 28 displays a recommended configuration for connection with an external resistor-
capacitor (RC) network.
VDD
R
XIN
C
Figure 28. Connecting the On-Chip Oscillator to an External RC Network
An external resistance value of 45 kï is recommended for oscillator operation with an
external RC network. The minimum resistance value to ensure operation is 40 kïï®ï The
typical oscillator frequency can be estimated from the values of the resistor (R in kï) and
capacitor (C in pF) elements using the following equation:
Oscillator Frequency (kHz)
=
----------------------1---ï´--1---0--6----------------------
ï¨0.4 ï´ R ï´ Cï© + ï¨4 ï´ Cï©
Figure 29 displays the typical (3.3 V and 25°C) oscillator frequency as a function of the
capacitor (C, in pF) employed in the RC network assuming a 45 Kï external resistor. For
very small values of C, the parasitic capacitance of the oscillator XIN pin and the printed
circuit board must be included in the estimation of the oscillator frequency.
It is possible to operate the RC oscillator using only the parasitic capacitance of the pack-
age and printed circuit board. To minimize sensitivity to external parasitics, external
capacitance values in excess of 20 pF are recommended.
PS022828-0413
P R E L I M I N A R Y Oscillator Operation with an External RC
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