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| MC68HC908AB32 Datasheet, PDF (141/392 Pages) Motorola, Inc – HCMOS Microcontroller Unit | |||
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Clock Generator Module (CGM)
⢠Crystal, X1
⢠Fixed capacitor, C1
⢠Tuning capacitor, C2 (can also be a fixed capacitor)
⢠Feedback resistor, RB
⢠Series resistor, RS (optional)
The series resistor (RS) 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
manufacturerâs data for more information.
Figure 9-3 also shows the external components for the PLL:
⢠Bypass capacitor, CBYP
⢠Filter capacitor, CF
Care should be taken with routing in order to minimize signal cross talk
and noise. (See 9.10 Acquisition/Lock Time Specifications for routing
information and more information on the filter capacitorâs value and its
effects on PLL performance).
SIMOSCEN
OSC1
RB
X1
C1
CGMXCLK
OSC2
VSSA
RS*
C2
CGMXFC
CF
VDDA
VDD
CBYP
*RS can be zero (shorted) when used with higher-frequency crystals. Refer to manufacturerâs data.
Figure 9-3. CGM External Connections
MC68HC908AB32 â Rev. 1.1
Freescale Semiconductor
Clock Generator Module (CGM)
Technical Data
141
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