MC68HC908LJ12 Datasheet, PDF (102/413 Pages) Freescale Semiconductor, Inc – 8-bit microcontroller units

Clock Generator Module (CGM)
8.3 Features
Features of the CGM include:
• Phase-locked loop with output frequency in integer multiples of an
integer dividend of the crystal reference
• Low-frequency crystal operation with low-power operation and
high-output frequency resolution
• Programmable prescaler for power-of-two increases in frequency
• Programmable hardware voltage-controlled oscillator (VCO) for
low-jitter operation
• Automatic bandwidth control mode for low-jitter operation
• Automatic frequency lock detector
• CPU interrupt on entry or exit from locked condition
• Configuration register bit to allow oscillator operation during stop
mode
8.4 Functional Description
The CGM consists of three major sub-modules:
• Oscillator module — The oscillator module generates the constant
reference frequency clock, CGMRCLK (buffered CGMXCLK).
• Phase-locked loop (PLL) — The PLL generates the
programmable VCO frequency clock, CGMVCLK, and the divided,
CGMPCLK. The CGMPCLK is one of the reference clocks to the
base clock selector circuit.
• Base clock selector circuit — This software-controlled circuit
selects the one of three clocks as the base clock, CGMOUT:
CGMXCLK, CGMXCLK divided by two, or CGMPCLK divided by
two.
Figure 8-1 shows the structure of the CGM.
Figure 8-2 is a summary of the CGM registers.
MC68HC908LJ12 — Rev. 2.1
Freescale Semiconductor
Clock Generator Module (CGM)
Technical Data
103