MC68HC08AZ16 Datasheet, PDF (107/527 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Clock Generator Module (CGM)
CGM external
connections
In its typical configuration, the CGM requires seven external
components. Five of these are for the crystal oscillator and two are for
the PLL.
The crystal oscillator is normally connected in a Pierce oscillator
configuration, as shown in Figure 3. This figure shows only the logical
representation of the internal components and may not represent actual
circuitry. The oscillator configuration uses five components:
• Crystal, X₁
• Fixed capacitor, C₁
• Tuning capacitor, C₂ (can also be a fixed capacitor)
• Feedback resistor, R_B
• Series resistor, R_S (optional)
The series resistor (R_S) is included in the diagram to follow strict Pierce
oscillator guidelines and may not be required for all ranges of operation,
especially with high frequency crystals. Refer to the crystal
manufacturer’s data for more information.
Figure 3 also shows the external components for the PLL:
• Bypass capacitor, C_BYP
• Filter capacitor, C_F
Care should be taken with routing in order to minimize signal cross talk
and noise. See Acquisition/lock time specifications on page 119 for
routing information and more information on the filter capacitor’s value
and its effects on PLL performance.
MC68HC08AZ32
106
Clock Generator Module (CGM)
12-cgm
MOTOROLA