MC68HC08XL36 Datasheet, PDF (90/362 Pages) Freescale Semiconductor, Inc – HCMOS Microcontroller Unit

CGM
Freescale Semiconductor, Inc.
6. Using the value 4.9152 MHz for f_nom, calculate the VCO linear
range multiplier, L. The linear range multiplier controls the
frequency range of the PLL.
L = round_{f-f-n}-^v--_oc--_ml-^k--_
Example: L = _{4----.-9-3---1-2--5--M-2----H-M----z-H----z--} = 7
7. Calculate the VCO center-of-range frequency, f_vrs. The
center-of-range frequency is the midpoint between the minimum
and maximum frequencies attainable by the PLL.
f_vrs = L × f_nom
Example: f_vrs = 7 × 4.9152 MHz = 34.4 MHz
NOTE:
For proper operation,
f_vrs – f_vclk ≤ -^f--ⁿ--₂-^o----^m---
Exceeding the recommended maximum bus frequency or VCO
frequency can crash the MCU.
8. Program the PLL registers accordingly:
a. In the upper four bits of the PLL programming register (PPG),
program the binary equivalent of N.
b. In the lower four bits of the PLL programming register (PPG),
program the binary equivalent of L.
Special
Programming
Exceptions
The programming method described in Programming the PLL on
page 89 does not account for two possible exceptions. A value of 0
for N or L is meaningless when used in the equations given. To
account for these exceptions:
• A 0 value for N is interpreted the same as a value of 1.
• A 0 value for L disables the PLL and prevents its selection as the
source for the base clock. (See Base Clock Selector Circuit on
page 91.)
MC68HC08XL36
90
Clock Generator Module (CGM)
For More Information On This Product,
Go to: www.freescale.com
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