+/+…when timing is critical
C9819
133 MHz I2C Clock Generator for Mobile Pentium®III / Rambus Systems
Preliminary
Spread Spectrum Clock Generation (SSCG)(Cont.)
In this device Spread Spectrum is enabled By I2C, byte0, bit0. At power up, this byte0, bit0 defaults to a high (Spread
Spectrum disabled), therefore, in order to enable the Spread Spectrum feature, byte0, bit0 must be programmed to a
low.
In Down Spread mode the center frequency is shifted down from its rested (non-spread) value by -0.25%. (ex.:
assuming the center frequency is 100MHz in non-spread mode; when down spread is enabled, the center frequency
shifts to 99.75MHz.).
In Center Spread mode, the Center frequency remains the same as in the non-spread mode.
Spread Spectrum effects only CPU, 3V66(0:2), PCI(_F,0:6), and IOAPIC(0:1) outputs.
Down Spread
Center Spread
Fig.6A
Fig.6B
Spread Spectrum Bandwidth Selection Table.
SST2 SST1 SST0
Bandwidth
+/- 0.625%
+/- 0.5%
+/-0.35%
+/-0.25%
-2.5%
Direction
Center
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
Center
Center
Center
Down
-1%
Down
- 0.7%
Down
- 0.5%
Down (default)
Table 4.
INTERNATIONAL MICROCIRCUITS, INC 525 LOS COCHES ST.
MILPITAS, CA 95035, USA TEL: 408-263-6300 FAX 408-263-6571
Rev 1.0
11/1/1999
Page 8 of 17
http://www.imicorp.com
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