HP dc7900 Power Control, Power Button Actions, Pressed Power Button Results, System State

Power and Signal Distribution

7.3Power Control

The generation of +3, +5, and +12 VDC is controlled digitally with the PS On signal. When the PS On signal is asserted, all DC voltages are produced. When PS On is de-asserted, only auxiliary power (+5 AUX) is generated. The +5 AUX voltage is always produced as long as the system is connected to a live AC source.

7.3.1 Power Button

The PS On signal is typically controlled through the Power Button which, when pressed and released, 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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