General Description
1.7.2.1 Crystal Resonator
The circuit in Figure 1-8 shows a crystal oscillator circuit for an AT-cut,
parallel resonant crystal. Follow the crystal supplier’s recommendations,
because the crystal parameters determine the external component
values required to provide reliable startup and maximum stability. The
load capacitance values used in the oscillator circuit design should
account for all stray layout capacitances. To minimize output distortion,
mount the crystal and capacitors as close as possible to the pins.
MCU
OSC1
10 MΩ∗
OSC2
22 pF∗
XTAL
2 MHz
22 pF∗
∗Starting value only. Follow crystal supplier’s
recommendations regarding component
values that will provide reliable startup and
maximum stability.
Figure 1-8. Crystal Connections
NOTE:
Use an AT-cut crystal and not a strip or tuning fork crystal. The MCU
might overdrive or have the incorrect characteristic impedance for a strip
or tuning fork crystal.
1.7.2.2 Ceramic Resonator
To reduce cost, use a ceramic resonator instead of a crystal. Use the
circuit shown in Figure 1-9 for a 2-pin ceramic resonator or the circuit
shown in Figure 1-10 for a 3-pin ceramic resonator, and follow the
resonator manufacturer’s recommendations.
The external component values required for maximum stability and
reliable starting depend upon the resonator parameters. The load
capacitance values used in the oscillator circuit design should include all
Technical Data
30
MC68HC705C4A • MC68HSC705C4A — Rev. 3.0
General Description
MOTOROLA