Hardware Reference
36
Fan control
The Q35 motherboards support three fan monitors that check the fan tachometer signals to
determine the fan’s rotational speed. The three monitors are assigned to the processor fan,
system fan 1, and system fan 2.
Fan speed modes are controlled in the BIOS setup utility, Advanced Features > Hardware
Monitor menu. By default, all fans run at the full speed.
Note: To configure the fan speed modes, be sure to use all 3-pin fans or all 4-pin fans.
Front panel connections and indicators
The Front panel I/O provides support for power switches and LED indicators via an internal 2x8-
pin header. See Front panel I/O header on page 46 for the pinout definitions of this header.
Power switch
If a soft-switched power supply is used, a momentary switch should be connected between
pins 1 and 2 of the power connector. When the switch is closed for more than about 4 seconds,
the motherboard powers off—regardless of the state of the operating system. (The action of the
switch is configurable in the BIOS.) This power off will cause any system context information to
be lost.
See ATX power connector (24-pin, 12V)) on page 45 and BIOS customization on page 40 for
the power connector pinouts.
Reset switch
If the reset switch is used, a momentary switch connected between pins 3 and 4 causes the
motherboard to restart when the switch is closed.
Power LED
Connect either a single-color LED (usually green) or a two-terminal dual-color LED (usually
green/yellow) to indicate the powered status of the Q35 motherboard. In both cases, the
“green“ cathode should be attached to pin 16 of the front panel I/O header.
Table 24 describes how the indicator is driven when operating with both single and dual-color
devices assuming the +5V standby power is available.
Table 24. Power state indicators
LED indicator LED state Description
Single-color Off The motherboard is powered down or in one of the ACPI sleep states.
On The motherboard is fully powered up.
Dual-color (green/
yellow)
Off The motherboard is powered down (S5).
Green The motherboard is fully powered up (S0).
Yellow The motherboard is in standby (S3) or hibernating (S4) state.
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