APPROVED PRODUCT
C9806J
SMBUS Frequency Clock Generator for Advanced Mobile Pentium
®
III Applications.
Dial-a-Frequency Feature (Cont.)
R
42
43
44
45
46
47
48
49
50
51
Min N
44
45
46
47
48
49
50
51
52
53
Max N
87
90
92
94
96
98
100
102
104
107
™
P is a large value PLL constant that depends on the last frequency selection achieved through the hardware selectors
(S1, S0). P value may be determined from the following table:
S(1:0)
00,01
10,11
6
P
48008000
96016000
Therefore, if a 145MHz (use 145x10 )value is desired, then we should apply 145 into equation 1, and start by choosing
R to be 47 (assume the last frequency selection has the value P = 96016000):
145X10 = 96016000 X N
47
6
=> N = 70.97775371
Since this N number must be entered in Binary, it can only be an integer, so it must be rounded up or down. Here we
can rounded it up to 71, which will give us an exact CPU frequency of:
Fcpu = 96016000 X N = 145.045 MHz (accuracy + 310 ppm)
47
If the above frequency is not accurate enough, then you must choose another R value and start from the beginning. For
example choose R = 49 and this will yield an N = 73.99808365, which is rounded to 74. If the 74 is applied in the
formula 1, then Fcpu = 145.0038 MHz(accuracy + 26 ppm).
Other R values within the above limits may also be evaluated.
Cypress Semiconductor Corporation
525 Los Coches St.
Milpitas, CA 95035. Tel: 408-263-6300, Fax: 408-263-6571
http://www.cypress.com
Document#: 38-07051 Rev. **
5/23/2001
Page 7 of 16
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