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Technical Reference Guide
Compaq iPAQ Family of Internet Devices
First Edition - March 2000
7-3
7.2.2 POWER CONTROL
The power supply assembly is controlled digitally by the PS On signal (Figure 7-1). When PS On
is asserted, the Power Supply Assembly is activated and all voltage outputs are produced. When
PS On is de-asserted, the Power Supply Assembly is off and no voltages (except +5 AUX) are
generated.
Note that the +5 AUX voltage is always produced as long as the system is
connected to a live AC source.
The PS On signal can be controlled either by the Power Button or by the operating system (OS).
7.2.2.1 Power Button Control
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. 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:
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.
Full On, ACPI Enabled (Pressed and Released in 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):
PS On is negated, de-activating the power supply.
Suspend, ACPI Enabled (Pressed and Released in Under Four Seconds):
System wakes up to Full On.
(Pressed and Held At least Four Seconds Before Release):
System powers off.
7.2.2.2 OS Power Control
The PS On signal can be de-asserted by the ACPI-compliant operating system such as Windows
95. This system uses ACPI mode as the default power management mode, allowing the operating
system to shut off the system (once the user has selected that decision) without further user
intervention.