7-4 www.hp.com Technical Reference Guide
Power and Signal Distribution
The +12Vsb (auxilary) voltage is always produced by the power supply unit as long as the
system is connected to a live AC source. When the PS On signal is asserted, the power supply
unit produces the +12 Vmain, +12 Vcpu, and -12 V outputs.
The standard 240-watt and 320-watt power suppies have a 70% minimum efficiency rating at
100% of the rated load, measured while operating from 100 VAC @60 Hz and 230 VAC @ 50
Hz.
The optional high-efficiency 240-watt and 320-watt power supplies operate at the following
efficiencies while operating from 100 VAC @60 Hz and 230 VAC @ 50 Hz :
100% of rated load: 85% efficient
50% of rated load: 89% efficient
20% of rated load: 87% efficient
7.4 Powe r Co ntrol
System power is controlled through the power button and though external events.
7.4.1 Power Button
Pressing and releasing the power button applies a negative (grounding) pulse to the power
control logic on the system board. The resultant action of pressing the power button depends on
the state and mode of the system at that time and is described as follows:
Table 7-4.
Power Button Actions
System State
Pressed Power Button Results In:
Off Negative pulse, of which the falling edge results in power control logic
asserting PS On signal to Power Supply Assembly, which then initializes. ACPI
four-second counter is not active.
On, ACPI Disabled Negative pulse, of which the falling edge causes power control logic to
de-assert the PS On signal. ACPI four-second counter is not active.
On, ACPI Enabled Pressed and Released Under Four Seconds:
Negative pulse, of which the falling edge causes power control logic to
generate SMI-, set a bit in the SMI source register, set a bit for button status,
and start four-second counter. Software should clear the button status bit within
four seconds and the Suspend state is entered. If the status bit is not cleared by
software in four seconds PS On is de-asserted and the power supply assembly
shuts down (this operation is meant as a guard if the OS is hung).
Pressed and Held At least Four Seconds Before Release:
If the button is held in for at least four seconds and then released, PS On is
negated, de-activating the power supply.
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