W254B Datasheet, PDF (11/16 Pages) SpectraLinear Inc – 133MHz Spread Spectrum FTG for Mobile Pentium® III Platforms

W254B
Byte 4: Control Register (1 = Enable, 0 = Disable)
Bit
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Pin#
19
-
-
-
-
-
-
Name
VCH_CLK SSC Mode
0 = 48 MHz non-SSC (default)
1 = 66 MHz SSC
Reserved Drive to ’0’
Reserved Drive to ’0’
Reserved Drive to ’0’
Reserved Drive to ’0’
Reserved Drive to ’0’
Reserved Drive to ’0’
Reserved Drive to ’0’
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
Bit 7
Bit 6
Bit 5
Bit 4
Pin#
-
-
-
-
Name
Pin Description
Reserved Drive to ‘0’
(Active/Inactive)
Spread Spectrum and Overclocking Mode (Active/Inactive)
Select. See Table 11
(Active/Inactive)
Reserved Drive to ’0’
(Active/Inactive)
Bit 3
Bit 2
Bit 1
Bit 0
-
Reserved Drive to ’0’
-
Reserved Drive to ’0’
Reserved Drive to ‘0’
-
Reserved Drive to ‘0’
(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%
overclocking upon power up, with either 0% or –0.5% spread
spectrum. (Spread spectrum ON/OFF remains under Byte 0,
bit 3 control). Note that 10% and 15% overclocking can only
be enabled with Spread Spectrum turned OFF.
Table 11.Spread Spectrum and Overclocking Mode Select
Byte 0
Byte 5
Bit 3
Bit 5 Bit 6
SS % Overclock %
Description and Comments
0
Spread
0
Spectrum
ON
1
1
0
–0.5%
0%
No overclocking (Default)
1
±0.5%
0%
No overclocking
0
–0.5%
5% ^[10]
1
±0.5%
5% ^[10]
0
0
Spread
0
1
Spectrum
OFF
1
0
1
1
-
0%
No overclocking
-
10% ^[10]
-
5% ^[10]
-
15% ^[10]
Note:
10. Overclocking not tested; characterized at room temperature only. Base Frequency determined through hardware select pins, FS0 & FS1.
Rev 1.0, November 20, 2006
Page 11 of 16