XC908AS60ACFU Motorola Semiconductor Products, XC908AS60ACFU Datasheet - Page 177

• Manufacturer Part Number: XC908AS60ACFU
• Description: MC68HC908AZ60A, MC68HC908AS60A Hcmos Microcontroller Unit Technical Data
• Manufacturer: Motorola Semiconductor Products

10.4.2.4 Programming the PLL
MC68HC908AZ60A — Rev 2.0
MOTOROLA
Use this 9-step procedure to program the PLL. The table below lists the
variables used and their meaning (Please also reference
page 172).
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
f
f
f
f
CGMRCLK
CGMVCLK
f
VCLKDES
Example: f
Example: f
calculate the VCO frequency multiplier, N. Round the result to the
nearest integer.
Variable
CGMVRS
BUSDES
f
f
NOM
BUS
Example: f
Clock Generator Module (CGM)
Example:
f
f
BUSDES
VCLKDES
VCLKDES
CGMVCLK
Table 10-2. Variable Definitions
CGMVCLK
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
N
= 8 MHz
N
= 4 × f
= 4 × 8 MHz = 32 MHz
=
=
=
= 8 × 4 MHz = 32 MHz
N f
-------------------------
f
f
CGMRCLK
32 MHz
------------------- -
VCLKDES
4 MHz
×
BUSDES
CGMRCLK
RCLK
CGMVCLK
, equal to the crystal frequency,
=
Definition
BUSDES
8
Clock Generator Module (CGM)
VCLKDES
.
.
Functional Description
.
Figure 10-1
Technical Data
177
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