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Subject:
From:
Oscar Viñas <[log in to unmask]>
Reply To:
PCBUILD - Personal Computer Hardware discussion List <[log in to unmask]>
Date:
Mon, 24 Jul 2000 13:22:24 -0400
Content-Type:
text/plain
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----- Original Message -----
From: Doug Simmons <[log in to unmask]>


> At 7/19/00 09:30 AM -0600, Bob Wright wrote:
>
> >I believe you mean NLX form factor...
> ><snip> The ATX form factor moves the switching
> >to the motherboard, allowing for the Bios and Operating System
> >to control power, (ie: the motherboard can be powered down
> >to sleep mode or turned off).
>
> I think this relates to my question on PCSOFT about Windows 98 doing the
> power off rather than display the "It is now Safe to Shutdown Your
> Computer" message.
>
> How does Windows 98 "know" that the computer is of the ATX form factor?
>
> Doug

The newer motherboard form factors, such as ATX and NLX, include special new
signals not present in previous Baby-AT or LPX form factors. One of them is
called PS_ON or Power_On (pin 14), the other is 5VSB or 5v_Standby (pin 9).
They both can be used to turn the power supply and the system on or off via
software. PS_ON is specially evident when you use it with an Operating
System that supports the Advanced Power Management - APM (Windows 95 and
later) or Advanced Configuration and Power Interface - ACPI (Windows 98 and
later) specifications. When you select the Shut Down option from the Start
menu, Windows automatically turns the computer off after it completes the
operating system shutdown sequence. A system without this feature only
displays a message that it is safe to shut down the PC.

The PS_ON signal is also used to power up the system. In these form factors,
the front panel Power switch doesn't physically control the power supply's
access to the 110v AC power. Instead, the power supply's on or off status is
toggled by a PS_ON active low signal received on pin 14 of the ATX connector
FROM the motherboard. The 5VSB signal on pin 9 is always active whenever the
power supply is connected to an AC power source. The 5VSB signal provides
the power for the remote switch  on the case to operate while the computer
is off and gives the motherboard a limited source of power even when off and
enabling new features to be implemented such as "Zero Voltage Modem Wake up"
or "LAN Wake up", in which a signal from a modem or network adapter can
actually cause a PC to wake up and power on. Another option is the Wake Up
Timer, which wakes up and power up your system at a predefined time for
specific application.

Oscar Viņas
University of Camaguey.
CUBA.

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