s908az32ag2cfue Freescale Semiconductor, Inc, s908az32ag2cfue Datasheet - Page 96

• Manufacturer Part Number: s908az32ag2cfue
• Description: M68hc08 Microcontrollers 8-bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Clock Generator Module (CGM)
8.3.2.5 Special Programming Exceptions
The programming method described in
exceptions. A value of 0 for N or L is meaningless when used in the equations given. To account for these
exceptions:
96
4. Calculate the VCO frequency, f
5. Calculate the bus frequency, f
6. If the calculated f
7. Using the value 4.9152 MHz for f
8. Calculate the VCO center-of-range frequency, f
9. Program the PLL registers accordingly:
•
•
another f
multiplier controls the frequency range of the PLL.
midpoint between the minimum and maximum frequencies attainable by the PLL.
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
8.3.3 Base Clock Selector
a. In the upper four bits of the PLL programming register (PPG), program the binary equivalent
b. In the lower four bits of the PLL programming register (PPG), program the binary equivalent
f
Example: f
CGMVRS
of N.
of L.
For proper operation,
Exceeding the recommended maximum bus frequency or VCO frequency
can crash the MCU.
RCLK
= L
.
CGMVRS
bus
×
f
NOM
is not within the tolerance limits of your application, select another f
= 7 × 4.9152 MHz = 34.4 MHz
Example: f
Example:
Circuit.
Example:
MC68HC908AZ32A Data Sheet, Rev. 2
BUS
f
f
BUS
CGMVCLK
CGMVCLK
f
NOM
CGMVRS
8.3.2.4 Programming the
L
, and compare f
CGMVCLK
=
=
, calculate the VCO linear range multiplier, L. The linear range
f
BUS
round
f
----------------------- -
L
CGMVCLK
.
=
–
=
=
NOTE
f
4
------------------------------- -
4.9152 MHz
CGMVCLK
= 8 × 4 MHz = 32 MHz
32 MHz
------------------- -
N f
⎛
⎝
32 MHz
f
----------------------- -
CGMVCLK
×
CGMVRS
4
f
BUS
NOM
CGMRCLK
with f
=
≤
. The center-of-range frequency is the
f
--------------- -
⎞
⎠
8 MHz
NOM
=
2
PLL, does not account for two possible
BUSDES
7
.
.
Freescale Semiconductor
BUSDES
or