MC68HC908AZ32ACFU MOTOROLA [Motorola, Inc], MC68HC908AZ32ACFU Datasheet - Page 143

• Manufacturer Part Number: MC68HC908AZ32ACFU
• Description: Microcontrollers
• Manufacturer: MOTOROLA [Motorola, Inc]

8.4.2.4 Programming the PLL
68HC908AZ32A — Rev 0.0
MOTOROLA
Use this 9-step procedure to program the PLL. The table below lists the
variables used and their meaning (Please also reference
page 138).
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
Freescale Semiconductor, Inc.
•
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f
f
f
CGMRCLK
f
CGMVCLK
f
VCLKDES
CPU interrupts from the CGM are disabled.
Example: f
Example: f
calculate the VCO frequency multiplier, N. Round the result to the
nearest integer.
Variable
CGMVRS
BUSDES
f
f
NOM
BUS
Clock Generator Module (CGM)
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Example:
f
BUSDES
VCLKDES
VCLKDES
Table 8-2. Variable Definitions
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
= 4
=
=
-------------------------
f
f
CGMRCLK
32 MHz
------------------- -
VCLKDES
4 MHz
f
8 MHz = 32 MHz
BUSDES
RCLK
CGMVCLK
, equal to the crystal frequency,
=
Definition
BUSDES
8
Clock Generator Module (CGM)
VCLKDES
.
.
Functional Description
.
Advance Information
Figure 8-1
on
143