Technical Reference Guide
Compaq Deskpro EP Series of Personal Computers
First Edition - April 1998
3-11
3.3.1.2 Processor Changing/Upgrading
The slot 1 design allows for easy changing and/or upgrading of the microprocessor/cache
complex. The 100-MHz Slot 1 system board functionally supports all current Pentium II series
processors. The mounting (retention) consideration for the Celeron processor is the same as that
which is discussed in section 3.2.3. When changing the processor, two key areas should be
considered: thermal characteristics and operating speed.
Thermal Considerations
The SEC cartridge includes a passive heat sink. The Pentium II processor includes an internal
temperature sensor that will shut down the CPU if the cartridge overheats. When the cartridge
temperature reaches 135°C the processor will assert the THERMTRIP signal that system board
logic uses to shut down the clock generator. The THERMTRIP signal is also used to activate the
circuit that causes the power LED to blink, indicating the excessive heat condition. Upgrade
processors may include a fan-cooled heat sink.
Processor Speed Selection
Changing the processor may require re-configuration of the bus/core frequency ratio. The 100-
MHz slot 1 system board includes a six-position DIP switch (SW), of which four positions are
used to select the bus-to-core frequency ratio of the Pentium II. Table 3-5 shows the possible
switch configurations for this system and the resultant core (or processing) frequency, based on
the bus frequency.
Table 3–5.
Pentium II Microprocessor Bus/Core Speed Switch Settings
Table 3-5.
100-MHz Slot 1 System Board
Bus/Core Speed Switch Settings
DIP SW1 Settings
2 3 4 5 [1]
Bus/Core
Freq. Ratio 66-MHz Bus 100-MHz Bus
1 0 0 0 1/3 200 300
1 1 0 0 2/7 233 350
0 0 1 0 1/4 266 400
0 1 1 0 2/9 300 450
1 0 1 0 1/5 333 500
NOTES:
Shipping configurations are unshaded. Board tested @ 100 MHz only.
[1] 0 = Switch Closed (On), 1 = Switch Open (Off)
The processor sets the clock generator to the appropriate bus frequency. Software can determine
the operating speed by reading the bus-to-core frequency ratio and the bus speed from an MSR
register in the processor.
NOTE:
The DIP switch settings should be set to match the processor installed.
Configuring for a speed higher than that which the processor is designed could result in
unreliable operation and possible system damage.
Core Fre
uenc
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