Z8F4822AR020SG Datasheet, PDF (216/323 Pages) Zilog, Inc. – High Performance 8-Bit Microcontrollers

Z8 Encore! XP^® F64xx Series
Product Specification
196
On-Chip Oscillator
The products in the Z8 Encore! XP F64xx Series feature an on-chip oscillator for use with
external crystals with frequencies from 32 kHz to 20 MHz. In addition, the oscillator can
support external RC networks with oscillation frequencies up to 4 MHz or ceramic resona-
tors with oscillation frequencies up to 20 MHz. This oscillator generates the primary sys-
tem 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 (32 kHz–
20 MHz). If an external clock generator is used, the X_OUT pin must be left unconnected.
When configured for use with crystal oscillators or external clock drivers, the frequency of
the signal on the X_IN input pin determines the frequency of the system clock (that is, no
internal clock divider). In RC operation, the system clock is driven by a clock divider
(divide by 2) to ensure 50% duty cycle.
Operating Modes
The Z8 Encore! XP F64xx Series products support four different oscillator modes:
• On-chip oscillator configured for use with external RC networks (<4MHz)
• Minimum power for use with very low frequency crystals (32kHz to 1.0MHz)
• Medium power for use with medium frequency crystals or ceramic resonators (0.5MHz
to 10.0 MHz)
• Maximum power for use with high frequency crystals or ceramic resonators (8.0MHz
to 20.0 MHz)
The oscillator mode is selected through user-programmable option bits. For more informa-
tion, see the Option Bits chapter on page 180.
Crystal Oscillator Operation
Figure 40 displays a recommended configuration for connection with an external funda-
mental-mode, parallel-resonant crystal operating at 20 MHz. Recommended 20 MHz crys-
tal specifications are provided in Table 105. Resistor R1 is optional and limits total power
dissipation by the crystal. The printed circuit board layout must add no more than 4 pF 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.
PS019924-0113
PRELIMINARY
On-Chip Oscillator