MC68HC908LJ12 Datasheet, PDF (105/413 Pages) Freescale Semiconductor, Inc – 8-bit microcontroller units

Clock Generator Module (CGM)
8.4.1 Oscillator Module
The oscillator module provides two clock outputs CGMXCLK and
CGMRCLK to the CGM module. CGMXCLK or CGMXCLK divide-by-two
can be selected to drive the SIM module to generate the system bus
clocks. CGMRCLK is the reference clock for the phase-lock-loop, to
generate a higher frequency clock. The oscillator module also provides
the reference clock for the real time clock (RTC) module.
See Section 7. Oscillator (OSC) for detailed description on oscillator
module. See Section 12. Real Time Clock (RTC) for detailed
description on RTC.
8.4.2 Phase-Locked Loop Circuit (PLL)
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.
8.4.3 PLL Circuits
The PLL consists of these circuits:
• Voltage-controlled oscillator (VCO)
• Reference divider
• Frequency pre-scaler
• Modulo VCO frequency divider
• Phase detector
• Loop filter
• Lock detector
Technical Data
106
Clock Generator Module (CGM)
MC68HC908LJ12 — Rev. 2.1
Freescale Semiconductor