Fan Control Device with Hardware Monitoring and Acoustic Noise Reduction Features
Datasheet
Table 7.14 Temperature Limit vs. Register Setting
LIMIT
LIMIT (DEC)
LIMIT (HEX)
-127°c
-127
81h
.
.
.
.
.
.
.
.
.
-50°c
-50
CEh
.
.
.
.
.
.
.
.
.
0°c
0
00h
.
.
.
.
.
.
.
.
.
50°c
50
32h
.
.
.
.
.
.
.
.
.
127°c
127
7Fh
7.2.21
Registers 6A-6Ch: Absolute Temperature Limit
Register
Address
Read/
Write
Bit 7
Bit 0
Default
Value
Register Name
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
(MSb)
(LSb)
6Ah
6Bh
6Ch
R/W
R/W
R/W
Zone 1 Temp Absolute Limit
Zone 2 Temp Absolute Limit
Zone 3 Temp Absolute Limit
7
7
7
6
6
6
5
5
5
4
4
4
3
3
3
2
2
2
1
1
1
0
0
0
64h
64h
64h
These registers become read only when the Lock bit is set. Any further attempts to write to these
registers shall have no effect.
In Auto Fan mode, if any zone associated with a PWM output exceeds the temperature set in the
Absolute limit register, all PWM outputs will increase their duty cycle to 100% except those that are
disabled via the PWM Configuration registers. This is a safety feature that attempts to cool the system
if there is a potentially catastrophic thermal event.
If an absolute limit register set to 80h (-128°c), the safety feature is disabled for the associated zone.
That is, if 80h is written into the Zone x Temp Absolute Limit Register, then regardless of the reading
register for the zone, the fans will not turn on-full based on the absolute temp condition.
Default =100°c=64h.
When any fan is in auto fan mode, then if the temperature in any zone exceeds absolute limit, all fans
go to full, including any in manual mode, except those that are disabled. Therefore, even if a zone is
not associated with a fan, if that zone exceeds absolute, then all fans go to full. In this case, the
absolute limit can be chosen to be 7Fh for those zones that are not associated with a fan, so that the
fans won't turn on unless the temperature hits 127 degrees.
SMSC EMC6D102
Revision 0.4 (04-05-05)
DATA6S5HEET
SMSC [ SMSC CORPORATION ]
