Clock Generator Module (CGMC)
Functional Description
MC68HC908GP32
•
MC68HC08GP32
—
Rev. 6
Technical Data
MOTOROLA
Clock Generator Module (CGMC)
115
6. Calculate and verify the adequacy of the VCO and bus
frequencies f
VCLK
and f
BUS
.
7. Select the VCO’s power-of-two range multiplier E, according to
this table:
8. Select a VCO linear range multiplier, L, where f
NOM
= 38.4 kHz
9. Calculate and verify the adequacy of the VCO programmed
center-of-range frequency, f
VRS
. The center-of-range frequency is
the midpoint between the minimum and maximum frequencies
attainable by the PLL.
For proper operation,
10. Verify the choice of P, R, N, E, and L by comparing f
VCLK
to f
VRS
and f
VCLKDES
. For proper operation, f
VCLK
must be within the
application’s tolerance of f
VCLKDES
, and f
VRS
must be as close as
possible to f
VCLK
.
NOTE:
Exceeding the recommended maximum bus frequency or VCO
frequency can crash the MCU.
Frequency Range
E
0 < f
VCLK
< 9,830,400
0
9,830,400
≤
f
VCLK
< 19,660,800
1
19,660,800
≤
f
VCLK
< 39,321,600
2
NOTE: Do not program E to a value of 3.
f
VCL K
2
P
N R
⁄
×
(
)
f
RCL K
×
=
f
BU S
f
VC LK
(
)
4
⁄
=
L
round
f
VCLK
2
E
f
NOM
×
--------------------------
=
f
VRS
L
2
E
×
(
)
f
NOM
=
f
VRS
f
VCLK
–
f
N OM
2
E
×
2
--------------------------
≤
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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