MC68HC08AZ32A Datasheet, PDF (125/456 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Clock Generator Module (CGM)
Functional Description
8.4.2.4 Programming the PLL
Use this 9-step procedure to program the PLL. The table below lists the
variables used and their meaning (Please also reference Figure 8-1).
Variable
f_BUSDES
f_VCLKDES
f_CGMRCLK
f_CGMVCLK
f_BUS
f_NOM
f_CGMVRS
Table 8-2. Variable Definitions
Definition
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
1. Choose the desired bus frequency, f_BUSDES.
Example: f_BUSDES = 8 MHz
2. Calculate the desired VCO frequency, f_VCLKDES.
f_VCLKDES = 4 × f_BUSDES
Example: f_VCLKDES = 4 × 8 MHz = 32 MHz
3. Using a reference frequency, f_RCLK, equal to the crystal frequency,
calculate the VCO frequency multiplier, N. Round the result to the
nearest integer.
N = _f--fC--^V--_G-^C---_ML---^K-_R--^D-_C--^E--_L-^S-_K--
Example: N = ^{3--4--2---M--M---H--H---z-z--} = 8
4. Calculate the VCO frequency, f_CGMVCLK.
f_CGMVCLK = N × f_CGMRCLK
Example: f_CGMVCLK = 8 × 4 MHz = 32 MHz
MC68HC08AZ32A — Rev 1.0
MOTOROLA
Clock Generator Module (CGM)
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Technical Data
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