+/+…when timing is critical
C9829B
Low EMI Clock Generator for Intel 133MHz/3DIMM Chipset Systems
Approved Product
Dial-a-Frequency™ Feature (Cont.)
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, bits7, 6, 5, 4). P value may be determined from the following
table:
S(3:0)
P
0000
0001, 1100
32005333
48008000
64010666
96016000
0010, 0011, 0100, 1000, 1111
0110, 0111, 0101, 1001, 1010, 1011, 1101, 1110
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
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.
INTERNATIONAL MICROCIRCUITS, INC. 525 LOS COCHES ST.,
MILPITAS, CA 95035, USA. TEL: 408-263-6300, FAX 408-263-6571
http://www.imicorp.com
Rev 1.3
4/12/2000
Page 11 of 20
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