W254B Datasheet, PDF (10/17 Pages) SpectraLinear Inc – 133MHz Spread Spectrum FTG for Mobile Pentium® III Platforms

W254B
Byte 3: Control Register (1 = Enable, 0 = Disable)
Bit
Pin#
Name
Bit 7
-
Reserved Drive to ’0’
Bit 6
13
PCI6
Bit 5
12
PCI5
Bit 4
11
PCI4
Bit 3
10
PCI3
Bit 2
8
PCI2
Bit 1
7
PCI1/FS1
Bit 0
--
SDRAM 133-MHz Mode Enable
Byte 4: Control Register (1 = Enable, 0 = Disable)
Bit
Pin#
Name
Bit 7
19
VCH_CLK SSC Mode
0 = 48 MHz non-SSC (default)
1 = 66 MHz SSC
Bit 6
-
Reserved Drive to ’0’
Bit 5
-
Reserved Drive to ’0’
Bit 4
-
Reserved Drive to ’0’
Bit 3
-
Reserved Drive to ’0’
Bit 2
-
Reserved Drive to ’0’
Bit 1
Reserved Drive to ’0’
Bit 0
-
Reserved Drive to ’0’
Pin Description
(Active/Inactive)
(Disabled/Enabled)
(Disabled/Enabled)
(Disabled/Enabled)
(Disabled/Enabled)
(Disabled/Enabled)
(Disabled/Enabled)
Default is Disabled = ‘0’, Enabled = ’1’
Pin Description
(Disabled/Enabled)
(Active/Inactive)
(Active/Inactive)
(Active/Inactive)
(Active/Inactive)
(Active/Inactive)
(Active/Inactive)
(Active/Inactive)
Byte 5: Control Register (1 = Enable, 0 = Disable)
Bit
Pin#
Name
Bit 7
-
Reserved Drive to ‘0’
Bit 6
-
Spread Spectrum and Overclocking
Bit 5
-
Mode Select. See Table 9
Bit 4
-
Reserved Drive to ’0’
Bit 3
-
Reserved Drive to ’0’
Bit 2
-
Reserved Drive to ’0’
Bit 1
Reserved Drive to ‘0’
Bit 0
-
Reserved Drive to ‘0’
Pin Description
(Active/Inactive)
(Active/Inactive)
(Active/Inactive)
(Active/Inactive)
(Active/Inactive)
(Active/Inactive)
(Active/Inactive)
(Active/Inactive)
Byte 5 has been provided as an optional register to enable a
greater degree of spread spectrum and overclocking perfor-
mance for all PLL1 outputs. (CPU, SDRAM, DCLK, APIC, PCI,
3V66 and VCH_CLK)
By enabling Byte 5, (bits 5 and 6) spread spectrum can be
increased to +0.5% and /or overclocking of either 5%, 10% or
15% can be enabled.
It is not necessary to access Byte 5 if these additional features
are not implemented. All outputs will default to 0% overclock-
ing upon power up, with either 0% or –0.5% spread spectrum.
Document #: 38-07233 Rev. *A
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