General Description
Functional Pin Description
MC68HC05P1A — Rev. 3.0
General Release Specification
MOTOROLA
General Description
21
NON-DISCLOSURE
AGREEMENT
REQUIRED
NOTE:
The frequency, fosc, of the oscillator or external clock source is divided
by two to produce the internal PH2 bus clock operating frequency, fop.
1.5.2.1 Crystal
The circuit in Figure 1-4 (a) shows a typical oscillator circuit for an AT-
cut, parallel resonant crystal. Follow the crystal manufacturer’s
recommendations, as the crystal parameters determine the external
component values required to provide maximum stability and reliable
startup. The load capacitance values used in the oscillator circuit design
should include all stray capacitances. Mount the crystal and components
as closely as possible to the pins for startup stabilization and to minimize
output distortion.
1.5.2.2 Ceramic Resonator
In cost-sensitive applications, use a ceramic resonator in place of a
crystal. Use the circuit in Figure 1-4 (a) for a ceramic resonator and
follow the resonator manufacturer’s recommendations, as the resonator
parameters determine the external component values required for
maximum stability and reliable starting. The load capacitance values
used in the oscillator circuit design should include all stray capacitances.
Mount the resonator and components as closely as possible to the pins
for startup stabilization and to minimize output distortion.
1.5.2.3 RC Oscillator
The lowest cost oscillator uses the RC mask option and an external
resistor. With this option, a resistor is connected to the oscillator pins, as
shown in Figure 1-4 (b). The relationship between R and fop is shown in Figure 1-5. Consult the factory for tolerance limits and design
specifications.
1.5.2.4 External Clock
An external clock from another CMOS-compatible device can be
connected to the OSC1 input, with the OSC2 input not connected, as