mc68hc08qa24 Freescale Semiconductor, Inc, mc68hc08qa24 Datasheet - Page 113

• Manufacturer Part Number: mc68hc08qa24
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

9.4.2.4 Programming the PLL
MC68HC08QA24
Freescale Semiconductor
NOTE:
Use this procedure to program the PLL:
The round function means that the result is rounded to the nearest
integer.
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
•
•
•
Software must wait a given time, t
before selecting the PLL as the clock source to CGMOUT
(BCS = 1).
The LOCK bit is disabled.
CPU interrupts from the CGM are disabled.
calculate the VCO frequency multiplier, N.
Clock Generator Module (CGM)
Example: f
Example: f
Example:
Example: f
f
N
VCLKDES
VCLKDES
f
=
VCLK
VC
round
=
LK
32 MHz
------------------- -
= 8 × 4 MHz = 32 MHz
BUSDES
4 MHz
= 4 × f
= 4 × 8 MHz = 32 MHz
=
XCLK



f
-------------------------- -
N f
VCLK
VCLKDES
f x
×
AL
BUSDES
, equal to the crystal frequency,
= 8 MHz
CLK
=
, after entering tracking mode
x
.
BUSDES
CLK
8 MHz
Clock Generator Module (CGM)
VCLKDES



.
.
Technical Data
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