mc68hc708mp16 Freescale Semiconductor, Inc, mc68hc708mp16 Datasheet - Page 111

• Manufacturer Part Number: mc68hc708mp16
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

8.4.2.4 Programming the PLL
MC68HC708MP16
Freescale Semiconductor
NOTE:
—
Rev. 3.1
The following procedure shows how to program the PLL.
The round function in the following equations means that the real
number should be rounded to the nearest integer number.
1. Choose the desired bus frequency, f
2. Calculate the desired VCO frequency (four times the desired bus
3. Choose a practical PLL reference frequency, f
4. Select a VCO frequency multiplier, N.
5. Calculate and verify the adequacy of the VCO and bus
6. Select a VCO linear range multiplier, L.
7. Calculate and verify the adequacy of the VCO programmed
8. Verify the choice of N and L by comparing f
frequency).
frequencies f
where f
center-of-range frequency f
f
application’s tolerance of f
possible to f
VCLKDES
Clock Generator Module (CGM)
NOM
. For proper operation, f
VCLK
= 4.9152 MHz
VCLK
.
f
VCLKDES
and f
N
L
f
f
VCLK
BUS
=
f
=
VRS
BUS
round
round
=
VCLKDES
=
.
=
VRS
= (L)f
(
N f
f
4 f
VCLK


.


×
f
--------------------- -
×
VCLKDES
f
------------ -
NOM
f
VCLK
VCLK
f
NOM
RCLK
RCLK
BUSDES
, and f
)
BUSDES
4 ⁄


must be within the
Clock Generator Module (CGM)


VRS
VCLK
.
must be as close as
RCLK
to f
.
VRS
Technical Data
and
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