C9630 Datasheet, PDF (8/18 Pages) Cypress Semiconductor – PC133 Clock Generator for SiS630/Pentium III & SiS540/Socket7 Applications

APPROVED PRODUCT
C9630
PC133 Clock Generator for SiS630/Pentium^®III & SiS540/Socket7 Applications
Dial-a-Frequency^™ Feature
SMBus Dial-a-frequency^™ feature is available in this device via byte7, and byte 8
These bytes allow the user to enter the N and R values that will allow them to program any CPU frequency
desired following the formula:
Fcpu = ^{P × N}
R
Where N and R values are programmed in binary into byte 7 for N and byte 8 for R. See table below for min and max
allowed values.
R
Min N Max N
42
44
87
43
45
90
44
46
92
45
47
94
46
48
96
47
49
98
48
50
100
49
51
102
50
52
104
51
53
107
P is a large value PLL constant that depends on the last frequency selection achieved through the hardware selectors
(S3, S2, S1, S0) or through the software selectors (byte0 , bits 7,6,5,4,2). P value may be determined from the following
table:
S(4:0)
00001, 00010, 00111, 01101, 10001,
10010, 10111, 11010, 11011, 11100,
11101, 11110, 11111
00000, 00011, 00110, 01010, 10000,
10101
00100, 00101, 01000, 01001, 01011,
01100, 01110, 01111, 10011, 10100,
10110, 11000, 11001
P
96016000
64010667
48008000
Therefore, if a 145MHz (use 145x10⁶ )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):
145X10⁶ = 96016000 X N
47
=> N = 70.97775371
Cypress Semiconductor Corporation
525 Los Coches St.
Milpitas, CA 95035. Tel: [phone], Fax: [phone]
http://www.cypress.com
Document#: 38-07035 Rev. **
05/02/2001
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