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Signal Description
2-12
82801AA and 82801AB Datasheet
2.17
Power and Ground
2.18
Pin Straps
2.18.1
Functional Strap
Table 2-18
shows signals that are used for static configuration. They are sampled at the rising edge
of PWROK to select configurations and then revert later to their normal usage. To envoke the
associated mode, the signal should be driven at least 4 PCI clocks prior to the time it is sampled.
Table 2-17. Power and Ground Signals
Name
Description
Vcc3_3
Power for Core:
3.3V. This power will be shut off in S3, S5, or G3 states.
Vcc1_8
Power for the Hub Interface:
1.8V. This power will be shut off in S3, S4, or G3 states.
VccSUS
Power for Resume Well:
3.3V. This power is not expected to be shut off unless the
system is unplugged.
VccRTC
Power for RTC Well:
3.3V. (Although can drop to 2.0V if the system is in G3 state). This
power is not expected to be shut off unless the RTC battery is removed or drained.
Note: Implementations should not attempt to clear CMOS by using a jumper to pull
VccRTC low. Clearing CMOS in an ICH-based platform can be done by using a jumper on
RTCRST# or GPI, or using SAFEMODE strap.
VBIAS
RTC Bias Voltage:
See
Section 2.12, “Real Time Clock Interface” on page 2-9
.
5VREF
Reference for 5V tolerance on inputs:
This power will be shut off in S3, S5, or G3
states.
HUBREF
Reference for the Hub Interface:
0.9V. This power will be shut off in S3, S4, or G3
states.
Vss
Grounds.
Table 2-18. Functional Strap Definitions
Signal
Usage
When Sampled
Comment
SPKR
NO
REBOOT
Rising Edge of
PWROK
The signal has a weak internal pull-up. If the signal is sampled
low, this indicates that the system is strapped to the “No
Reboot” mode (ICH will disable the TCO Timer system reboot
feature). The status of this strap is readable via the
NO_REBOOT bit (bit 1, D31: F0, Offset D4h).
AC_SDOUT
SAFE
MODE
Rising Edge of
PWROK
The signal has a weak internal pull-down. If the signal is
sampled high, the ICH will set the processor speed strap pins
for safe mode. Refer to processor specification for speed
strapping definition. The status of this strap is readable via the
SAFE_MODE bit (bit 2, D31: F0, Offset D4h).