MC68HC908AS60MFN MOTOROLA [Motorola, Inc], MC68HC908AS60MFN Datasheet - Page 157

• Manufacturer Part Number: MC68HC908AS60MFN
• Description: HCMOS Microcontroller Unit
• Manufacturer: MOTOROLA [Motorola, Inc]

10.4 Functional Description
10.4.1 Crystal Oscillator Circuit
MC68HC908AS60 — Rev. 1.0
MOTOROLA
The CGM consists of three major submodules:
Figure 10-1
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 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 percent 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.
1. Crystal oscillator circuit — The crystal oscillator circuit generates
2. Phase-locked loop (PLL) — The PLL generates the
3. Base clock selector circuit — This software-controlled circuit
Freescale Semiconductor, Inc.
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the constant crystal frequency clock, CGMXCLK.
programmable VCO frequency clock CGMVCLK.
selects either CGMXCLK divided by two or the VCO clock,
CGMVCLK, divided by two as the base clock, CGMOUT. The
system clocks are derived from CGMOUT.
Clock Generator Module (CGM)
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shows the structure of the CGM.
Clock Generator Module (CGM)
Functional Description
Technical Data
157