W254B Datasheet, PDF (9/17 Pages) SpectraLinear Inc – 133MHz Spread Spectrum FTG for Mobile Pentium® III Platforms

W254B
W254B Serial Configuration Map
1. The serial bits will be read by the clock driver in the following
order:
Byte 0 - Bits 7, 6, 5, 4, 3, 2, 1, 0
Byte 1 - Bits 7, 6, 5, 4, 3, 2, 1, 0
Byte N - Bits 7, 6, 5, 4, 3, 2, 1, 0
2. All unused register bits (reserved and N/A) should be writ-
ten to a “0” level.
3. All register bits labeled “Initialize to 0" must be written to
zero during initialization. Failure to do so may result in high-
er than normal operating current.
Byte 0: Control Register (1 = Enable, 0 = Disable)^[9]
Bit
Pin#
Name
Pin Description
Bit 7
19
VCH_CLK
(Active/Inactive)
Bit 6
--
Reserved Drive to ’0’
(Active/Inactive)
Bit 5
43
CPU_F
(Disabled/Enabled)
Bit 4
44
CPU
(Disabled/Enabled)
Bit 3
--
Spread Spectrum (1 = On; 0 = Off) (Active/Inactive)
Bit 2
22
DOT (48 MHz)
(Disabled/Enabled)
Bit 1
21
USB (48 MHz)
(Disabled/Enabled)
Bit 0
--
Reserved Drive to ’0’
(Active/Inactive)
Byte 1: Control Register (1 = Enable, 0 = Disable)^[9]
Bit
Pin#
Name
Bit 7
--
Reserved Drive to ’0’
Bit 6
--
Reserved Drive to ’0’
Bit 5
33
SDRAM5
Bit 4
34
SDRAM4
Bit 3
36
SDRAM3
Bit 2
37
SDRAM2
Bit 1
39
SDRAM1
Bit 0
40
SDRAM0
Pin Description
(Active/Inactive)
(Active/Inactive)
(Disabled/Enabled)
(Disabled/Enabled)
(Disabled/Enabled)
(Disabled/Enabled)
(Disabled/Enabled)
(Disabled/Enabled)
Byte 2: Control Register (1 = Enable, 0 = Disable)^[9]
Bit
Pin#
Name
Pin Description
Bit 7
17
3V66_AGP
(Disabled/Enabled)
Bit 6
16
3V66_1
(Disabled/Enabled)
Bit 5
15
3V66_0
(Disabled/Enabled)
Bit 4
--
Reserved Drive to ’0’
(Active/Inactive)
Bit 3
--
Reserved Drive to ’0’
(Active/Inactive)
Bit 2
--
Reserved Drive to ’0’
(Active/Inactive)
Bit 1
--
Reserved Drive to ’0’
(Active/Inactive)
Bit 0
--
Reserved Drive to ’0’
(Active/Inactive)
Note:
9. Inactive means outputs are held LOW and are disabled from switching. These outputs are designed to be configured at power-on and are not expected to be
configured during the normal modes of operation.
Document #: 38-07233 Rev. *A
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