Advance Information MC68HC908MR16/MC68HC908MR32 — Rev. 4.0
120 Clock Generator Module (CGM) MOTOROLA
Clock Generator Module (CGM)
The crystal oscillator is normally connected in a Pierce oscillator
configuration, as shown in Figure 8-3. Figure 8 -3 shows only the logical
representation of the internal components and may not represe nt actual
circuitry.
Figure 8-3. CGM External Connections
The oscillator configuration uses five components:
1. Crystal, X1
2. Fixed capacitor, C1
3. Tuning capacitor, C2 (can also be a fixed capacitor)
4. Feedback resistor, RB
5. Series resistor, RS (optional)
The series resistor (RS) is included in the diagram to follow strict Pierce
oscillator guidelines and may not be requir ed for all ranges of o peration,
especially with high-frequency crystals. Refer to the crystal
manufacturer’s data for more information.
C1 C2
CF
SIMOSCEN CGMXCLK
RB
X1
RS*CBYP
OSC1 OSC2 VSS CGMXFC VDDA
*RS can be 0 (shorted) when used with higher-frequency crystals.
VDD
Refer to manufacturer’s data.