F81866A Datasheet, PDF (35/210 Pages) Feature Integration Technology Inc. – 6 UARTs Super IO With 128 Bytes FIFO and Power

F81866A
T OVT
T Hhys
T HIGH
T Hhys
PME#
(pulse mode)
*
*
*
*
*Interrupt Reset when Interrupt Status Registers are written 1
Fig 6-4
6.4.1.3Fan
Fan speed count
Inputs are provided by the signals from fans equipped with tachometer outputs. The level of
these signals should be set to TTL level, and maximum input voltage cannot be over 5V. If the input
signals from the tachometer outputs are over the 5V, the external trimming circuit should be added to
reduce the voltage to obtain the input specification.
Determine the fan counter according to:
Count = ^{1.5 × 106}
RPM
In other words, the fan speed counter (12 bit resolution) has been read from register, the fan
speed can be evaluated by the following equation.
RPM = ^{1.5 × 106}
Count
As for fan, it would be best to use 2 pulses (4 phases fan) tachometer output per round. So the
parameter “Count” under 5 bit filter is 4096~64 and RPM is 366~23438 based on the above equation. If
using 8 phases fan, RPM would be from 183~11719.
Fan speed control
The F81866A provides 2 fan speed control methods:
1. DAC FAN CONTROL2. PWM DUTY CYCLE
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Jan, 2012
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