MC68HC708XL36 FREESCALE [Freescale Semiconductor, Inc], MC68HC708XL36 Datasheet - Page 89

• Manufacturer Part Number: MC68HC708XL36
• Description: HCMOS Microcontroller Unit
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

7-cgm1m_a
MOTOROLA
The operating range of the VCO is programmable for a wide range of
frequencies and for maximum immunity to external noise, including
supply and CGMXFC noise. The VCO frequency is bound to a range
from roughly one-half to twice the center-of-range frequency, f
Modulating the voltage on the CGMXFC pin changes the frequency
within this range. By design, f
frequency, f
CGMRCLK is the PLL reference clock, a buffered version of CGMXCLK.
CGMRCLK runs at a frequency, f
buffer. The buffer output is the final reference clock, CGMRDV, running
at a frequency f
The VCO’s output clock, CGMVCLK, running at a frequency f
back through a programmable modulo divider. The modulo divider
reduces the VCO clock by a factor, N. The divider’s output is the VCO
feedback clock, CGMVDV, running at a frequency f
Programming the PLL
The phase detector then compares the VCO feedback clock, CGMVDV,
with the final reference clock, CGMRDV. 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
CGMXFC based on the width and direction of the correction pulse. The
filter can make fast or slow corrections depending on its mode,
described in
of the external capacitor and the reference frequency determines the
speed of the corrections and the stability of the PLL.
The lock detector compares the frequencies of the VCO feedback clock,
CGMVDV, and the final reference clock, CGMRDV. Therefore, the
speed of the lock detector is directly proportional to the final reference
frequency f
condition based on this comparison.
Freescale Semiconductor, Inc.
For More Information On This Product,
rdv
nom
Go to: www.freescale.com
Acquisition and Tracking Modes
. The circuit determines the mode of the PLL and the lock
, (4.9152 MHz) times a linear factor L, or (L)f
rdv
= f
rclk
CGM
.
on page 92 for more information.)
vrs
is equal to the nominal center-of-range
rclk
, and is fed to the PLL through a
on page 90. The value
vdv
Functional Description
= f
MC68HC708XL36
vclk
nom
/N. (See
vclk
vrs
.
, is fed
.
CGM
89