Z8F6421PM020SC Datasheet, PDF (227/299 Pages) Zilog, Inc. – High Performance 8-Bit Microcontrollers Z8 Encore-R 64K Series

Z8 Encore!^® 64K Series
Product Specification
207
Oscillator Operation with an External RC Network
The External RC oscillator mode is applicable to timing insensitive applications.
Figure 41 illustrates a recommended configuration for connection with an external resis-
tor-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 45kΩ is recommended for oscillator operation with an
external RC network. The minimum resistance value to ensure operation is 40kΩ. 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 illustrates the typical (3.3V and 25⁰C) oscillator frequency as a function of the
capacitor (C in pF) employed in the RC network assuming a 45kΩ external resistor. For
very small values of C, the parasitic capacitance of the oscillator XIN 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 20pF are recommended.
PS019915-1005
On-Chip Oscillator