W83791D Information Storage Devices, Inc, W83791D Datasheet - Page 28

• Manufacturer Part Number: W83791D
• Description: Hardware Monitor With Speech Synthesizer And Asf Functions
• Manufacturer: Information Storage Devices, Inc

6.7
6.7.1 Fan speed count
tachometer outputs. The level of these signals should be set to TTL level, and the maximum input voltage should 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 meet the input specification. The normal circuit and trimming circuits are
shown as Figure 8.
Determine the fan counter according to:
In other words, if the fan speed counter has been read from register CR[28] or CR[29] or CR[2A] or CR[BA] or
CR[BB] , then the fan speed can be evaluated by the following equation.
bits for divisor. This 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.
Divisor
1
2 (default)
4
8
16
32
64
128
W83791D support 5 sets of fan counting. Fan inputs are provided for signals from fans equipped with
The default divisor is 2 and defined at CR47.bit7~4, CR4B.bit7~6, and Bank0 CR5D.bit5~7 which are three
FAN Speed Count and FAN Speed Control
Nominal RPM
8800
4400
2200
1100
550
275
137
68
Time
Revolution
6.82 ms
13.64 ms
27.27 ms
54.54 ms
109.08 ms
218.16 ms
436.32 ms
872.64 ms
Count
RPM
per
Count
Table 2.
RPM
21
. 1
. 1
Counts
153
153
153
153
153
153
153
153
35
35
Divisor
Divisor
10
10
6
6
Publication Release Date: Aug, 2001
70% RPM
6160
3080
1540
770
385
192
96
48
Time for 70%
9.74 ms
19.48 ms
38.96 ms
77.92 ms
155.84 ms
311.68 ms
623.36 ms
1246.72 ms
W83791D
Preliminary
Revision 0.41