Motorola MC68HC908GP32 Technical Data Manual page 116

Clock Generator Module (CGMC)
Technical Data
114
Freescale Semiconductor, Inc.
P, the power of two multiplier, and N, the range multiplier, are
integers.
In cases where desired bus frequency has some tolerance,
choose f to a value determined either by other module
RCLK
requirements (such as modules which are clocked by CGMXCLK),
cost requirements, or ideally, as high as the specified range
allows. See Section 23. Electrical
reference divider, R = 1. After choosing N and P, the actual bus
frequency can be determined using equation in 2 above.
When the tolerance on the bus frequency is tight, choose f
an integer divisor of f
requirement, use the following equation to solve for R with
practical choices of f
lowest R.
R = round R
MAX
4. Select a VCO frequency multiplier, N.
N
Reduce N/R to the lowest possible R.
5. If N is < N , use P = 0. If N > N
max
N max
N max
N max
Then recalculate N:
Clock Generator Module (CGMC)
For More Information On This Product,
Go to: www.freescale.com
Specifications. Choose the
, and R = 1. If f
BUSDES
, and choose the f
RCLK
 

f
VCLKDES
×
  –
 ------------------------- -
integer
f
 

RCLK
×
 
R f
VCLKDES
 
------------------------------------ -
= round
 f 
RCLK
, choose P using this table:
max
Current N Value
≤
0 < N N max
≤ ×
< N N max 2
× ≤ ×
2 < N N max 4
× ≤ ×
4 < N N max 8
×

R f
VCLKDES

N = round ------------------------------------ -
P

×
f 2
RCLK
MC68HC908GP32
RCLK
cannot meet this
RCLK
that gives the
RCLK
 

f
VCLKDES
 
------------------------- - 
f
 

RCLK
P
0
1
2
3



MC68HC08GP32 Rev. 6
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