w83627thg Winbond Electronics Corp America, w83627thg Datasheet - Page 33

• Manufacturer Part Number: w83627thg
• Description: Winbond Lpc I/o
• Manufacturer: Winbond Electronics Corp America

5.4
5.4.1
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’t be over VCC. 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
5-4 ~ 5-7.
Determine the fan counter according to:
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.
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, RPM, and count
FAN Speed Count and FAN Speed Control
Fan speed count
Pentium II/III
Bipolar Transistor
Temperature Sensor
B
CPU
OR
Therminal
Diode
C
E
2N3904
D+
D-
RPM
Count
R=30K,1%
=
=
Figure 5-3
Count
RPM
C=3300pF
- 26 -
1 35 10
. 1
.
35
R=30K,1%
×
×
×
×
W83627THF/W83627THG
C=3300pF
Divisor
Divisor
10
6
6
VREF
VTIN
CPUTIN
AGND
W83627THF