Z8F0830HH020SG Datasheet, PDF (175/257 Pages) Zilog, Inc. – High-Performance 8-Bit Microcontrollers

Z8 Encore!^® F0830 Series
Product Specification
157
Crystal Oscillator
The products in the Z8 Encore! F0830 Series contain an on-chip crystal oscillator for use
with external crystals with 32 kHz to 20 MHz frequencies. In addition, the oscillator sup-
ports external RC networks with oscillation frequencies up to 4 MHz or ceramic resonators
with frequencies up to 8 MHz. The on-chip crystal oscillator can be used to generate the
primary system clock for the internal eZ8 CPU and the majority of its 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 remain unconnected.
The on-chip crystal oscillator also contains a clock filter function. To see the settings for
this clock filter, see Table 90 on page 133. By default, however, this clock filter is dis-
abled; therefore, no divide to the input clock (namely, the frequency of the signal on the
X_IN input pin) can determine the frequency of the system clock when using the default set-
tings.
Note:
Although the X_IN pin can be used as an input for an external clock generator, the CLKIN
pin is better suited for such use. See the System Clock Selection section on page 151 for
more information.
Operating Modes
The Z8 Encore! F0830 Series products support the following four OSCILLATOR Modes:
• Minimum power for use with very low frequency crystals (32kHz to 1MHz)
• Medium power for use with medium frequency crystals or ceramic resonators (0.5MHz
to 8 MHz)
• Maximum power for use with high frequency crystals (8MHz to 20MHz)
• On-chip oscillator configured for use with external RC networks (<4MHz)
The OSCILLATOR Mode is selected using user-programmable Flash option bits. See the
Flash Option Bits chapter on page 124 for more information.
Crystal Oscillator Operation
The XTLDIS Flash option bit controls whether the crystal oscillator is enabled during
reset. The crystal may later be disabled after reset if a new oscillator has been selected as
the system clock. If the crystal is manually enabled after reset through the OSCCTL Reg-
PS025113-1212
Crystal Oscillator