mc68hc908as60 Freescale Semiconductor, Inc, mc68hc908as60 Datasheet - Page 163

• Manufacturer Part Number: mc68hc908as60
• Description: Mc68hc908as60 Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

10.4.2.4 Programming the PLL
MC68HC908AS60 — Rev. 1.0
Use this 9-step procedure to program the PLL.
variables used and their meaning.
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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Example: f
f
Example: f
calculate the VCO frequency multiplier, N. Round the result to the
nearest integer.
VCLKDES
Clock Generator Module (CGM)
f
Variable
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f
VCLKDES
BUSDES
f
f
f
f
f
RCLK
VCLK
NOM
BUS
VRS
= 4
Example: f
BUSDES
VCLKDES
Table 10-1. Variable Definitions
f
Example:
BUSDES
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
= 8 MHz
= 4
N
f
VCLK
VCLK
=
f
----------------------
8 MHz = 32 MHz
N
VCLKDES
= 8
f
=
RCLK
=
RCLK
N
32 MHz
------------------- -
4 MHz
VCLK
4 MHz = 32 MHz
Definition
f
RCLK
, equal to the crystal frequency,
.
BUSDES
Clock Generator Module (CGM)
VCLKDES
=
Table 10-1
8
.
Functional Description
.
lists the
Technical Data