W83627G Winbond Electronics Corp America, W83627G Datasheet - Page 39

• Manufacturer Part Number: W83627G
• Description: LPC Interface I/O plus Game Port, MIDI Port, Pb-free package
• Manufacturer: Winbond Electronics Corp America

7.4
7.4.1
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 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
8.4.
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 fol-
lowed table is an example for the relation of divisor, PRM, and count.
Fan speed count
FAN Speed Count and FAN Speed Control
Pentium II
Bipolar Transistor
Temperature Sensor
Therminal
B
Diode
CPU
OR
C
E
2N3904
D+
D-
RPM
Count
=
=
Count
Figure. 8.3
R=30K, 1%
RPM Divisor
- 35 -
1 35 10
1 35 10
.
.
R=30K, 1%
×
×
×
×
Divisor
C=3300pF
6
C=3300pF
6
W83627HF/ F/ HG/ G
Publication Release Date: June 09, 2006
VREF
VTINx
VTINx
W83627HF
Revision 2.27