XC68HC08KH12 Motorola, XC68HC08KH12 Datasheet - Page 91

• Manufacturer Part Number: XC68HC08KH12
• Description: MICROCONTROLLER
• Manufacturer: Motorola

8.4.1 Crystal Oscillator Circuit
8.4.2 Phase-Locked Loop Circuit (PLL)
8.4.3 PLL Circuits
MC68HC(7)08KH12
MOTOROLA
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Rev. 1.0
The crystal oscillator circuit consists of an inverting amplifier and an
external crystal. The OSC1 pin is the input to the amplifier and the OSC2
pin is the output. The SIMOSCEN signal from the system integration
module (SIM) enables the crystal oscillator circuit.
The CGMXCLK signal is the output of the crystal oscillator circuit and
runs at a rate equal to the crystal frequency. CGMXCLK is then buffered
to produce CGMRCLK, the PLL reference clock.
CGMXCLK can be used by other modules which require precise timing
for operation. The duty cycle of CGMXCLK is not guaranteed to be 50%
and depends on external factors, including the crystal and related
external components. An externally generated clock also can feed the
OSC1 pin of the crystal oscillator circuit. Connect the external clock to
the OSC1 pin and let the OSC2 pin float.
The PLL is a frequency generator that can operate in either acquisition
mode or tracking mode, depending on the accuracy of the output
frequency. The PLL can change between acquisition and tracking
modes either automatically or manually.
The PLL consists of these circuits:
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Voltage-controlled oscillator (VCO)
Reference divider
Frequency prescaler
Modulo VCO frequency divider
Phase detector
Loop filter
Lock detector
Clock Generator Module (CGM)
Clock Generator Module (CGM)
Functional Description
Advance Information
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