ADT7476
Rev. B | Page 41 of 72
05382-051
FRONT
CHASSIS
FAN
TACH2
ADT7476
PWM3
PWM2
REAR
CHASSIS
FAN
AMBIENT
TEMPERATURE
TACH3
D1+
D1–
V
CC
+5V
IN
+12V
IN
/VID5
GND
PWM1
TACH1
VID[0:4]/VID[0.5]
D2+
D2–
THERM
SDA
SCL
PROCHOT
5(VRM9)/6(VRM10)
CPU FAN
CPU
ICH
Figure 50. Recommended Implementation 2
STEP 2: CONFIGURING THE MUX
After the system hardware configuration is determined, the fans
can be assigned to particular temperature channels. Not only
can fans be assigned to individual channels but the behavior of
the fans is also configurable. For example, fans can be run
under automatic fan control, can be run manually (under
software control), or can be run at the fastest speed calculated
by multiple temperature channels. The mux is the bridge
between temperature measurement channels and the three
PWM outputs.
Bits [7:5] (BHVR) of Register 0x5C, Register 0x5D, and
Register 0x5E (PWM configuration registers) control the
behavior of the fans connected to the PWM1, PWM2, and
PWM3 outputs. The values selected for these bits determine
how the mux connects a temperature measurement channel to a
PWM output.
Automatic Fan Control Mux Options
Bits [7:5] (BHVR),
Register 0x5C, Register 0x5D, and
Register 0x5E.
000 = Remote 1 temperature controls PWMx
001 = Local temperature controls PWMx
010 = Remote 2 temperature controls PWMx
101 = Fastest speed calculated by local and Remote 2
temperature controls PWMx
110 = Fastest speed calculated by all three temperature
channels controls PWMx
The fastest speed calculated options pertain to controlling one
PWM output based on multiple temperature channels. The
thermal characteristics of the three temperature zones can be
set to drive a single fan. An example is the fan turning on when
Remote 1 temperature exceeds 60°C or if the local temperature
exceeds 45°C.
Other Mux Options
Bits [7:5] (BHVR), Register 0x5C, Register 0x5D, and
Register 0x5E.
011 = PWMx runs full speed
100 = PWMx is disabled (default)
111 = manual mode. In manual mode, PWMx runs under
software control. In this mode, PWM duty cycle registers
(Register 0x30 to Register 0x32) are writable and control
the PWM outputs.
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