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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, manually (under
software control), or 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.
REMOTE1 =
AMBIENT TEMP
LOCAL =
VRM TEMP
REMOTE2 =
CPU TEMP
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THERMAL CALIBRATION
100%
0%
T
T
MIN
RANGE
THERMAL CALIBRATION
100%
MUX
0%
T
T
MIN
RANGE
THERMAL CALIBRATION
100%
0%
T
T
MIN
RANGE
Figure 51. Assigning Temperature Channels to Fan Channels
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ADT7476A
Automatic Fan Control Mux Options
[7:5] (BHVR), Register 0x5C, Register 0x5D,
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 would be the fan
turning on when Remote 1 temperature exceeds 60°C or if
the local temperature exceeds 45°C.
Other Mux Options
[7:5] (BHVR), Register 0x5C, Register 0x5D,
Register 0x5E.
011 = PWMx runs full speed
100 = PWMx disabled (default)
111 = Manual mode. PWMx is running under
software control. In this mode, PWM current
duty cycle registers (0x30 to 0x32) are writable
and control the PWM outputs.
MUX
PWM
MIN
PWM
CONFIG
PWM
S
GENERATOR
ENHANCEMENT)
TACHOMETER1
MEASUREMENT
PWM
MIN
PWM
CONFIG
PWM
S
GENERATOR
ENHANCEMENT)
TACHOMETER2
MEASUREMENT
PWM
MIN
PWM
CONFIG
PWM
S
GENERATOR
ENHANCEMENT)
TACHOMETER3
AND 4
MEASUREMENT
38
RAMP
CONTROL
PWM1
(ACOUSTIC
TACH1
CPU FAN SINK
RAMP
CONTROL
PWM2
(ACOUSTIC
TACH2
RAMP
FRONT CHASSIS
CONTROL
PWM3
(ACOUSTIC
TACH3
REAR CHASSIS
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