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Processor Speed Selection
The Pentium II-based system board includes a six-position DIP switch (SW1), of which four
positions are used to select the bus-to-core frequency of the Pentium II. Table 3-2 shows the
possible switch configurations for this system and the resultant core (or processing) frequency.
Table 3–2. Pentium II Microprocessor Bus/Core Speed Switch Settings
Pentium II Microprocessor
Bus/Core Speed Switch Settings
DIP SW1 Settings
2 3 4 5 [1]
0 1 0 0
1 0 0 1
1 0 0 0
1 1 0 1
1 1 0 0
0 0 1 1
0 0 1 0
0 1 1 1
0 1 1 0
1 0 1 1
1 0 1 0
1 1 1 1
1 1 1 0
NOTES:
Shipping configurations are unshaded.
[1] 0 = Switch Closed (On), 1 = Switch Open (Off)
The status of SW1(2-4, 5) is readable through general-purpose I/O (GPIO) port 78h bits <3..0>,
allowing BIOS and/or diagnostic software to check an installed microprocessor with the switch
configuration. Table 3-3 shows the switch position-to-GPIO-to-I/O port 78h input wiring.
Table 3–3. SW2 Bus/Core Speed Positions to GPIO Assignments
SW1 Bus/Core Speed Positions
to GPIO Assignments
Switch Position
Signal Name
SW1-2
CFG_IGNNE
SW1-3
CFG_INTR
SW1-4
CFG_A20M
SW1-5
CFG_SPD60
Table 3-2.
Host Bus
Speed (MHz)
Core Speed (MHz)
66
60
66
60
66
60
66
60
66
60
66
60
66
Table 3-3.
GPIO Number
11
10
13
12
Compaq Deskpro 4000 and 6000 Personal Computers
featuring the Pentium II Processor
First Edition - October 1997
Technical Reference Guide
166
180
200
210
233
240
266
270
300
300
333
330
366
I/O Port 78h
bit <1>
bit <0>
bit <3>
bit <2>
3-5
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