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 XIN input pin can also
accept a CMOS-level clock input signal (32kHz-20MHz). If an external clock generator is
used, the XOUT pin must be left unconnected. The Z8F640x family device does not con-
tain in internal clock divider. The frequency of the signal on the XIN 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
XIN or XOUT pins. If oscillation does not occur, reduce the values of capacitors C1 and C2
to decrease loading.
PS017610-0404
On-Chip Oscillator
ZILOG [ ZILOG, INC. ]
