
SiS5595 PCI System I/O Chipset
Preliminary V2.0 Nov. 2, 1998 25 Silicon Integrated Systems Corporation
Enable(18h.9)
Status(14h.9)
Trigger Mode Logic
(Edge/Toggle trigger)
GPIO9/THRM#
I/O Selection(20h.9=1)
Input Mode
Output Pin Status(1Ch)
No Used
Input Pin
Status(1Ch.9)
Polarity
Selection(24h.9)
GPIO9/THRM#(28h.9)
1ms CLK PCI CLK
GPIO9 Event
Figure 3.2-8 Thermal Detection Logic
Power Button
This button is a user interface control instead of the traditional power supplier switch. It can
be used to cycle the system between the G0 and G1 state, as one of the power
management events. Besides, the power button provides user a mechanism to force the
system to enter the G2 State (Soft-Off) when the system has hung. This is called as power
button over-ride.
Normally, the SiS5595 generates a power button event in the form of SCI, or SMI# in the G0
working state while detecting the Press-and-Release sequence on the PWRBT# pin.
However, by setting bit 4 of ACPI register 13 to 1, the power button event can be generated
simply upon that the button is pressed. Upon the instant that power button is pressed to the
instant that the power button override event is recognized, the specific routine can be
invoked, and executed (due to SMI#, or SCI) to do any housekeeping before the power is
removed.
A 1ms de-bouncer associated with the power button is used to recognize and respond to the
active low logic presented on the pin. If the PWRBT# is pressed for more than 4 seconds,
the SiS5595 will turn off the system power by de-asserting the PS_ON#.
If the PWRBT# is released within 4 seconds, only the PWRBTN_STS bit (ACPI: 00h[8]) will
be set. If the PWRBTN_EN bit (ACPI: 02h[8]) is also enabled, an SMI# or SCI will be raised.
There is a power button over-ride enable bit in ACPI Register 13h bit 5, which is enabled by
default. Although the ACPI SPEC 1.0 no longer requires the support of this power button
over-ride enable bit, SiS5595 keeps the bit in other location to allow the application software
to disable the function just in case.
Power Management Timer
The SiS5595 supports a 24-bit power management timer, based on a 3.579545MHz clock,
which provides an accurate time value used by system software to measure and profile
system idleness (along with other tasks) while the system is in the working (G0) state. To
allow software to extend the number of bits in the timer, the power management timer