W83627HF Datasheet, PDF (114/185 Pages) Winbond – WINBOND I/O

W83627HF/F
PRELIMINARY
Bipolar Transistor
Temperature Sensor
C
B
2N3904
E
OR
Pentium II
CPU
D+
Therminal
Diode
D-
R=30K, 1%
VREF
C=3300pF
VTINx
R=30K, 1%
W83627HF
C=3300pF
VTINx
Figure 11.3
11.4 FAN Speed Count and FAN Speed Control
11.4.1 Fan speed count
Inputs are provides for signals from fans equipped with tachometer outputs. The level of these signals
should be set to TTL level, and maximum input voltage can not be over +5.5V. If the input signals
from the tachometer outputs are over the VCC, the external trimming circuit should be added to
reduce the voltage to obtain the input specification. The normal circuit and trimming circuits are
shown as Figure 11.4.
Determine the fan counter according to:
Count = ^{1.35 × 106}
RPM × Divisor
In other words, the fan speed counter has been read from register CR28 or CR29 or CR2A, the fan
speed can be evaluated by the following equation.
R P M = ^{1.35 × 10 6}
Count × Divisor
The default divisor is 2 and defined at CR47.bit7~4, CR4B.bit7~6, and Bank0 CR5D.bit5~7 which are
three bits for divisor. That provides very low speed fan counter such as power supply fan. The
followed table is an example for the relation of divisor, PRM, and count.
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Publication Release Date: Jul 1999
Revision 0.53