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4.8.5
TEMPERATURE SENSING
This system employs two sensors for monitoring the temperature inside the chassis. A thermister
attached to the heat sink of the Pentium II SEC cartridge is used to detect the caution level. This
thermister, connected to the system board through header P15, is part of sensing logic that
provides input to a Compaq ASIC. The sensing logic is set to trip when 179.6 F (82 C) is
reached. At that time the Compaq ASIC can generate an SMI (if so configured, see registers
below) resulting in a warning to the user and/or the FAN being turned on.
The Pentium II processor contains a sensor utilized to detect a deadly condition. This sensor will
activate when 135 C is reached. At that time the processor will produce the THERMTRIP-
signal. The assertion of THERMPTRIP- is recorded in a Compaq ASIC (see following registers)
and also results in turning off the system's clock generator, effectively shutting down the system.
The following two indexed registers are used by BIOS and available to software for controlling
the temperature sense function.
I/O Port C51.02h, Temperature Status/Clear Register
Bit
Function
7..2
Reserved
1
Temperature Deadly (RO)
0 = Normal
1 = Critical temperature detected
0
Reserved
NOTE: Bits 1,0 are cleared when read but will be instantly reset if condition remains.
I/O Port C51.03h, Temperature Interrupt/SMI Enable Register
Bit
Function
7..3
Reserved
2
Temperature Deadly Shutdown Disable:
0 = Initiate shutdown w/deadly condition.
1 = Do not initiate shutdown.
1,0
Reserved
4.8.6
COVER LOCK
The chassis cover can be locked to prevent unauthorized personnel from removing the cover and
changing the system hardware. The locking mechanism consists of a solenoid controlled by the
GPOC register of CM logic in the Compaq ASIC.
Compaq Deskpro 4000 and 6000 Personal Computers
featuring the Pentium II Processor
First Edition–- October 1997
Technical Reference Guide
4-49
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