Product Description
43
1.14.2.2 Fan Connectors
The D850MD and D850MV boards have two fan connectors with thermal control signals (fan 1
and fan 2) that are used to switch the fans on and off as determined by the thermal sensors.
The ambient temperature of a D850MD- or D850MV-based system is thermally monitored by
separate temperature sensors that control voltage to the fan 1 and fan 2 connectors. If the fans
attached to these connectors provide a tachometer signal, the sensor reports the fan speed to the
hardware monitor component.
The temperature sensors that control the fans are initialized by the BIOS at power-up to turn on
only when the sensor reaches 36
o
C (96.8
o
F). The fans switch off when their respective sensors
cool down to 31
o
C (87.8
o
F). This prevents the fans from turning off and on when the ambient air
around the sensor fluctuates around 35–36
o
C. When the fans switch on, they may appear to rotate
slowly because the fan’s duty cycle starts at 70 percent and rises to 100 percent when the sensor
reaches 46
o
C (114.8
o
F).
Table 12 summarizes the functions of the four fan connectors.
Table 12. Fan Connector Descriptions
Feature
Processor
Fan Fan 1 Fan 2 Fan 3
(Note 1)
+12 V DC connection Yes Yes Yes Yes
Tachometer output Yes No Yes No
Controllable No Yes Yes Yes
(Note 2)
Fan is on in the ACPI S0 or S1 states Yes Yes Yes Yes
Fan is off in the ACPI S3, S4, and S5 states Yes Yes Yes Yes
Notes:
1. This fan is present on the D850MV board only.
2. Fan 3 uses the same controls as fan 2. If fan 2 is switched off, fan 3 is also off.
For information about Refer to
The location of the fan connectors Figure 14, page 60
The signal names of the fan connectors Section 2.8.2.3, page 58
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