Z8F4822AR020SG Datasheet, PDF (218/323 Pages) Zilog, Inc. – High Performance 8-Bit Microcontrollers

Z8 Encore! XP^® F64xx Series
Product Specification
198
Oscillator Operation with an External RC Network
The External RC Oscillator mode is applicable to timing-insensitive applications.
Figure 41 displays a recommended configuration for connection with an external resistor-
capacitor (RC) network.
V_DD
R
X_IN
C
Figure 41. Connecting the On-Chip Oscillator to an External RC Network
An external resistance value of 45 kΩ is recommended for oscillator operation with an
external RC network. The minimum resistance value to ensure operation is 40 kΩThe
typical oscillator frequency can be estimated from the values of the resistor (R in kΩ) and
capacitor (C in pF) elements using the following equation:
Oscillator Frequency (kHz)
=
---------------------1----^---1---0---6----------------------
0.4  R  C + 4  C
Figure 42 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 kΩ external resistor. For
very small values of C, the parasitic capacitance of the oscillator X_IN pin and the printed
circuit board should 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.
PS019924-0113
P R E L I M I N A R Y Oscillator Operation with an External RC