W83783S_07 WINBOND [Winbond], W83783S_07 Datasheet - Page 18

• Manufacturer Part Number: W83783S_07
• Description: Winbond H/W Monitoring IC
• Manufacturer: WINBOND [Winbond]

6.4 FAN Speed Count and FAN Speed Control
6.4.1 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
13.
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, PRM, and count.
2 (default)
DIVISOR
128
16
32
64
1
4
8
NOMINAL
8800
4400
2200
1100
PRM
550
275
137
68
REVOLUTION
109.08 ms
218.16 ms
436.32 ms
872.64 ms
TIME PER
RPM
13.64 ms
27.27 ms
54.54 ms
6.82 ms
Count
=
=
Count
Table 1
RPM Divisor
1 35 10
- 14 -
1 35 10
.
.
×
COUNTS
×
×
×
Divisor
153
153
153
153
153
153
153
153
6
6
Publication Release Date: August 21, 2007
70% RPM
6160
3080
1540
770
385
192
96
48
TIME FOR 70%
W83783S
1246.72 ms
155.84 ms
311.68 ms
623.36 ms
19.48 ms
38.96 ms
77.92 ms
9.74 ms
Revision 1.0