mc68hc708mp16 Freescale Semiconductor, Inc, mc68hc708mp16 Datasheet - Page 113

• Manufacturer Part Number: mc68hc708mp16
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

8.4.4 CGM External Connections
MC68HC708MP16
Freescale Semiconductor
—
Rev. 3.1
selection or deselection of the VCO clock. The VCO clock also cannot
be selected as the base clock source if the factor L is programmed to a
zero. 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.
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
representation of the internal components and may not represent actual
circuitry. The oscillator configuration uses five components:
The series resistor (R
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 8-3
Routing should be done with great care to minimize signal cross talk and
noise. (See
information and more information on the filter capacitor’s value and its
effects on PLL performance.)
•
•
•
•
•
•
•
Crystal, X
Fixed capacitor, C
Tuning capacitor, C
Feedback resistor, R
Series resistor, R
Bypass capacitor, C
Filter capacitor, C
Clock Generator Module (CGM)
also shows the external components for the PLL:
8.10 Acquisition/Lock Time Specifications
1
S
) is included in the diagram to follow strict Pierce
S
F
1
(optional)
2
Figure
BYP
B
(can also be a fixed capacitor)
8-3.
Figure 8-3
Clock Generator Module (CGM)
shows only the logical
for routing
Technical Data
113