Z8F1601 Datasheet, PDF (183/246 Pages) Zilog, Inc. – Z8 Encore Microcontrollers with Flash Memory and 10-Bit A/D Converter

Z8F640x/Z8F480x/Z8F320x/Z8F240x/Z8F160x
Z8 Encore!^®
165
On-Chip Oscillator
The Z8F640x family devices feature an on-chip oscillator for use with an external 1-
20MHz crystal. This oscillator generates the primary system clock for the internal eZ8
CPU and the majority of the on-chip peripherals. Alternatively, the X_IN input pin can also
accept a CMOS-level clock input signal (32kHz-20MHz). If an external clock generator is
used, the X_OUT pin must be left unconnected. The Z8F640x family device does not con-
tain in internal clock divider. The frequency of the signal on the X_IN input pin determines
the frequency of the system clock. The Z8F640x family device on-chip oscillator does not
support external RC networks or ceramic resonators.
20MHz Crystal Oscillator Operation
Figure 90 illustrates a recommended configuration for connection with an external
20MHz, fundamental-mode, parallel-resonant crystal. Recommended crystal specifica-
tions are provided in Table 99. Resistor R₁ limits total power dissipation by the crystal.
Printed circuit board layout should add no more than 4pF of stray capacitance to either the
X_IN or X_OUT pins. If oscillation does not occur, reduce the values of capacitors C₁ and C₂
to decrease loading.
PS017610-0404
On-Chip Oscillator