MC68HC908AS60ACFN FREESCALE [Freescale Semiconductor, Inc], MC68HC908AS60ACFN Datasheet - Page 134

• Manufacturer Part Number: MC68HC908AS60ACFN
• Description: M68HC08 Microcontrollers
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

Clock Generator Module (CGM)
factor L is programmed to a 0. This value would set up a condition inconsistent with the operation of the
PLL, so that the PLL would be disabled and the crystal clock would be forced as the source of the base
clock.
10.3.4 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 10-3
actual circuitry. The oscillator configuration uses five components:
The series resistor (R
crystals. Refer to the crystal manufacturer’s data for more information.
Figure 10-3
Routing should be done with great care to minimize signal cross talk and noise. (See
Acquisition/Lock Time Specifications
value and its effects on PLL performance).
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Crystal, X
Fixed capacitor, C
Tuning capacitor, C
Feedback resistor, R
Series resistor, R
Bypass capacitor, C
Filter capacitor, C
shows only the logical representation of the internal components and may not represent
also shows the external components for the PLL:
*R
S
can be 0 (shorted) when used with higher-frequency crystals. Refer to manufacturer’s data.
1
SIMOSCEN
MC68HC908AZ60A • MC68HC908AS60A • MC68HC908AS60E Data Sheet, Rev. 6
S
) may not be required for all ranges of operation, especially with high-frequency
C
S
F
1
1
(optional)
2
BYP
B
(can also be a fixed capacitor)
R
X
1
B
Figure 10-3. CGM External Connections
for routing information and more information on the filter capacitor’s
R
C
S
2
*
CGMXCLK
C
F
Freescale Semiconductor
10.9
C
BYP
V
DD
Figure
10-3.