Chapter 18:
Temperature sensor and user
jumper
Description
The temperature sensor is a thermometer located on the board away from
the CPU. The user can set an upper and lower temperature limit. If the
temperature measured exceeds the upper limit the OS bit becomes active,
indicating an over-temperature condition. The OS bit remains active until
the measured temperature falls below the lower limit. By reading the OS
bit to see if it is set or not, an external device such as a fan can be
activated or deactivated.
The user jumper is W12[7–8]. The INT17 functions provide an easy
method to implement software routines according to whether or not a
jumper has been installed.
Temperature sensor INT17h function
definitions
The temperature sensor allows you to set over and under temperature
limits, and to read the ambient temperature. There is also a configuration
register. For complete details on the configuration register, refer to the
Dallas Semiconductor DS1775 SOT23 Digital Thermometer and
Thermostat Product Review sheet.
Digital data is written to/read from the component with MSb first, in
two’s complement format, with the MSb denoting positive or negative
temperature. All temperatures are in Celsius.
Write TEMP SENSOR register pointer
Function:
0edh
Subfunction:
00h
Purpose:
To set the TEMP SENSOR pointer to internal
registers
Calling Registers:
AH
0edh
AL
00h
BH
Number of bits in internal register 8
or 16. Only the configuration
register is 8 bit, all others are 16
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