mc68hc908jb16 Freescale Semiconductor, Inc, mc68hc908jb16 Datasheet - Page 251

• Manufacturer Part Number: mc68hc908jb16
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

13.3.3 Reference Divider
13.3.4 VCO Frequency Divider
13.3.5 Phase Detector
13.3.6 Phase Detector Filter
13.3.7 Lock Detector
MC68HC908JB16
Freescale Semiconductor
—
Rev. 1.1
The crystal oscillator frequency (OSCXCLK) is fed to the phase detector
through a 10-bit programmable divider module R. The divider output
(CGMRCLK) is equal to CGMXCLK divided by R and is used as the final
reference signal for the phase detector.
The VCO output clock (CGMVCLK) is fed to the phase detector through
another 12-bit programmable divider module N. The divider output
(CGMFCLK) is equal to CGMVCLK divided by N and it is the feedback
signal for the phase detector.
The phase detector compares the VCO feedback clock with the final
reference clock. A correction pulse is generated based on the phase
difference between the two signals. The loop filter then slightly alters the
DC voltage on the external capacitor connected to pin CGMXFC base
on the width and direction of the correction pulse.
The loop filter controls the dynamic characteristics of the PLL. The loop
filter can make fast or low corrections depending on whether the phase
detector is unlocked or stable.
The lock detector compares the frequencies of the VCO feedback clock,
CGMFCLK, and the final reference clock, CGMRCLK. Therefore, the
speed of the lock detector is directly proportional to the final reference
clock, CGMRCLK.
Clock Generator Module (CGM)
Clock Generator Module (CGM)
Technical Data
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