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Chapter 4 System Support
High and low thermal parameters are programmed into the ASIC by BIOS during POST. If the
and the Therm-
signal will be asserted. The asserted Therm- signal can, with the proper software setup, be used by
NOTE: These systems do not support thermister-based fans used on earlier products.
high thermal parameter is reached then the fan(s) will be turned on full speed
the 82801 ICH2 to initiate an AOL message for transmission over a network (refer to Network
Interface Controller subsection in Chapter 5).
Fan Header
F a Control Block Diagram
Figure 4 iagram
igure 4-11. Sm ll Form Factor Fan
Fan CMD
Fan
Control
C ASI
Fan
Sense
SMBus
82801
Therm-
10
+5 VDC
(+)
Interrupt
P1
Fan CMD
Processor
rol
IC
Cont
AS
Sink
Chassis
Fan Sense
(+)
2
SMBus
Therm-
2
CPU Fan Sense
+5 VDC
+5 VDC
82
ICH2
Power Supply Assembly
Speed
Control
SPD
Speed
Processor
(+)
(-)
ICH2
P1
13
PS Fan
Control
(-)
3
2
1
P70
Fan
Sink
PS
Circuits
+5 VDC
Power Supply Assembly
Speed
Control
Fan
SPD
PS
Circuits
(+)
(-)
Fan
(-)
3
1
Chassis Fan
Header P8
(-)
(+)
3
1
CPU Fan Header
P70
+5 VDC
12
24
PS Fan
801
-12. Desktop/Configurable Minitower Fan Control Block D
Compaq Evo and Workstation Personal Computers
Featuring the Intel Pentium 4 Processor
Second Edition – January 2003
4-30