w83l784r Winbond Electronics Corp America, w83l784r Datasheet - Page 21

• Manufacturer Part Number: w83l784r
• Description: Winbond H/w Monitoring Ic
• Manufacturer: Winbond Electronics Corp America

6.5 FAN Speed Count and FAN Speed Control
6.5.1 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 15.
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 CR49.bit0~2, bit4~6 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)
Confidential, For Beta-site Only
Divisor
128
16
32
64
1
4
8
Nominal
PRM
8800
4400
2200
1100
550
275
137
68
Revolution
109.08 ms
218.16 ms
436.32 ms
872.64 ms
Count
Time per
RPM
13.64 ms
27.27 ms
54.54 ms
6.82 ms
-20 -
Count
Table 2.
RPM
1 35
1 35 10
.
.
Counts
Divisor
Divisor
10
153
153
153
153
153
153
153
153
6
6
70% RPM
Publication Release Date: Sep.
6160
3080
1540
770
385
192
96
48
W83L784R
Preliminary
Time for 70%
1246.72 ms
155.84 ms
311.68 ms
623.36 ms
Revision 0.54
19.48 ms
38.96 ms
77.92 ms
9.74 ms
1999