Temperature Sensing - Compaq EN Series Technical Reference Manual

4.8.5

TEMPERATURE SENSING

This system is designed to support Deschutes-generation Pentium II processors, which employ a
diode (internal to the SEC cartridge) for detecting the caution level. The diode is part of sensing
logic that provides input to a System Security ASIC.
NOTE: A Celeron processor with compatible packaging and heatsinking can be
installed in this system.
The sensing logic is set to trip when 179.6 °F (82 °C) is reached. At that time the System
Security ASIC can generate an SMI (if so configured, see registers below) resulting in a warning
to the user. Two general purpose input ports of the 82371south bridge monitor status of the
Thermal Caution circuitry. They are listed below with their default values:
1. 82371 GPI #20 – Thermal Caution event status (0 = caution event has not occurred)
2. 82371 GPI #21 – Thermal sensor connection status (0 = connected)
The Pentium II processor contains a sensor utilized to detect a deadly condition. When the
processor temperature reaches 275 °F (135 °C) the THERMTRIP- signal is asserted and
recorded in the System Security ASIC (see following registers). Assertion of THERMTRIP- also
results in turning off the system's clock generator, effectively shutting down the system. The
Deadly condition is indicated by the power LED blinking a 4-Hz rate.
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: Bit 1 is 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
Compaq Deskpro EN Series o Personal Computers
Net PC and Small Form Factor Models
First Edition - June 1998
Technical Reference Guide
4-53