MC68HC08AS32A Datasheet, PDF (103/296 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Clock Generator Module (CGM)
Functional Description
NOTE:
3. Using a reference frequency, f_RCLK, equal to the crystal frequency, calculate
the VCO frequency multiplier, N.
The round function means that the result is rounded to the nearest integer.
N
=
r
o
u
n
d



f--_{V----fC--R--L--C-K--L-D--K--E----S- }
Example: N = ^{3----2-----M-----H----z--} = 8
4 MHz
4. Calculate the VCO frequency, f_VCLK.
f_VCLK = N × f_RCLK
Example: f_VCLK = 8 × 4 MHz = 32 MHz
5. Calculate the bus frequency, f_BUS, and compare f_BUS with f_BUSDES. If the
calculated f_BUS is not within the tolerance limits of your application, select
another f_BUSDES or another f_RCLK.
f_BUS
=
f---_{V---C---L---K-}
4
Example:
f_BUS
=
3----2-----M-----H----z--
4
=
8 MHz
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
=
r
ou

nd

f-f-_{V-N---C-O---L-M--K- }
Example: L = ------3----2-----M-----H----z------- = 7
4.9152 MHz
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: Exceeding the recommended maximum bus frequency or VCO frequency can
crash the MCU.
MC68HC08AS32A — Rev. 1
MOTOROLA
Clock Generator Module (CGM)
For More Information On This Product,
Go to: www.freescale.com
Data Sheet
103