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© Andigilog, Inc. 2006
www.andigilog.com
October 2006 - 70A05007
aSC7611
Register 62, 63h: Min/Off, Spike Smoothing
Register
Address
Read/
Write
Register
Name
Bit 7
(MSB)
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
(LSB)
Default
Value
Lock
62h
R/W
Min/Off,
Zone1 Spike
Smoothing
OFF3
OFF2
OFF1
RES
ZN1E
ZN1-2
ZN1-1
ZN1-0
00
X
63h
R/W
Zone2 Spike
Smoothing
ZN2E
ZN2-2
ZN2-1
ZN2-0
ZN3E
ZN3-2
ZN3-1
ZN3-0
00
X
The OFF1-OFF3 (Bits 7 to 5) specifiy whether the duty cycle will be 0% or Minimum Fan Duty when the measured
temperature falls below the Temperature LIMIT register setting (see Table 15 below).
If the Remote pins are connected to a processor or chipset, instantaneous temperature spikes may be sampled by the
aSC7611. Fan speed algorithm has two phases of filtering on temperature zone readings. First, a “No-Spike” value is
created from the current temperature and three previous readings. This is an average of the two remaining values when the
high and low values are removed. This is the temperature used to determine PWM and is always running.
The second phase is a user specified filter and coefficient. This filter determines a smoothed temperature value, Smooth Ti,
by taking the No-Spike Ti, subtracting the previous smoothed temperature, Smooth Ti-1, divided by 2^N and adding that to
the previously smoothed temperature. N and GAIN are coefficients selected internally to provide the spike filter smoothing
time constants shown in Table 14, designated ZN1-2:ZN1-0 for Zone 1, ZN2-2:ZN2-0 for Zone 2 and ZN3-2:ZN3-0 for Zone
3.
For the current temperature reading Ti:
No-Spike Ti = (Discard min and max of (Ti, Ti-1, Ti-2, Ti-3))/2
Smooth Ti = GAIN * (No-Spike Ti - Smooth Ti-1)/2
N + Smooth Ti-1
If these spikes are not filtered, the CPU fan (if connected to aSC7611) may turn on prematurely or produce unpleasant
noise. For this reason, any zone that is connected to a chipset or processor should have spike smoothing enabled.
Individual system characteristics will determine how large this coefficient should be.
When spike smoothing is enabled, the temperature reading registers will still reflect the current value of the temperature –
not the “smoothed out” value.
ZN1E, ZN2E and ZN3E enable temperature smoothing for zones 1, 2 and 3 respectively.
ZN1-2, ZN1-1 and ZN1-0 control smoothing time for Zone 1.
ZN2-2, ZN2-1 and ZN2-0 control smoothing time for Zone 2.
ZN3-2, ZN3-1 and ZN3-0 control smoothing time for Zone 3.
These registers become read-only when the Ready/Lock/Start/Override register Lock bit is set. Any further attempts to write
to these registers shall have no effect.
0
10
20
30
40
50
60
1
23
4
56
78
9 10 11 12
Figure 10 Representation of What Temperature Is Passed to the aSC7611 Auto Fan Control with (green)
and without (red dashed) Spike Smoothing
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