MC68HC908AS60ACFN FREESCALE [Freescale Semiconductor, Inc], MC68HC908AS60ACFN Datasheet - Page 132

• Manufacturer Part Number: MC68HC908AS60ACFN
• Description: M68HC08 Microcontrollers
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

Clock Generator Module (CGM)
10.3.2.4 Programming the PLL
Use this 9-step procedure to program the PLL.
(Please also reference
132
1. Choose the desired bus frequency, f
2. Calculate the desired VCO frequency, f
3. Using a reference frequency, f
4. Calculate the VCO frequency, f
5. Calculate the bus frequency, f
6. If the calculated f
multiplier, N. Round the result to the nearest integer.
another f
Example:
Example:
Example: f
RCLK
MC68HC908AZ60A • MC68HC908AS60A • MC68HC908AS60E Data Sheet, Rev. 6
.
CGMVCLK
f
f
f
BUSDES
VCLKDES
VCLKDES
Figure
bus
f
f
Variable
f
f
CGMRCLK
CGMVCLK
f
VCLKDES
CGMVRS
BUSDES
is not within the tolerance limits of your application, select another f
f
f
NOM
BUS
10-1).
= 8 × 4 MHz = 32 MHz
= 8 MHz
= 4 × f
= 4 × 8 MHz = 32 MHz
Example:
Table 10-2. Variable Definitions
BUS
f
Example:
RCLK
f
BUS
Desired Bus Clock Frequency
Desired VCO Clock Frequency
Chosen Reference Crystal Frequency
Calculated VCO Clock Frequency
Calculated Bus Clock Frequency
Nominal VCO Center Frequency
Shifted VCO Center Frequency
CGMVCLK
CGMVCLK
BUSDES
, and compare f
N
, equal to the crystal frequency, calculate the VCO frequency
=
BUSDES
f
=
BUS
f
----------------------- -
VCLKDES
CGMVCLK
-------------------------
f
.
Table 10-2
f
N
CGMRCLK
VCLKDES
=
=
4
=
.
32 MHz
------------------- -
N f
32 MHz
------------------- -
4 MHz
×
.
4
Definition
BUS
CGMRCLK
lists the variables used and their meaning
with f
=
=
8 MHz
8
BUSDES
.
Freescale Semiconductor
BUSDES
or