82801BA Datasheet, PDF (50/498 Pages) Intel Corporation – Intel 82801BA I/O Controller Hub 2 (ICH2) and Intel 82801BAM I/O Controller Hub 2 Mobile

Signal Description
2.20 Pin Straps
2.20.1 Functional Straps
The following signals 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 invoke the
associated mode, the signal should be driven at least 4 PCI clocks prior to the time it is sampled.
Table 2-20. Functional Strap Definitions
Signal
Usage
When
Sampled
Comment
AC_SDOUT
SAFE
MODE
Rising
Edge of
PWROK
EE_DOUT Reserved
FS[0]
Reserved
GNT[A]#
Top-Swap
Override
Rising
Edge of
PWROK
HLCOMP
Enhanced
Hub
Interface
Mode
During
PCIRST#
assertion
SPKR
No
Reboot
Rising
Edge of
PWROK
The signal has a weak internal pull-down. If the signal is sampled
high, the ICH2 sets 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).
System designers should include a placeholder for a pull-down
resistor on EE_DOUT but do not populate the resistor.
System designers should include a placeholder for a pull-down
resistor on FS[0] but do not populate the resistor.
The signal has a weak internal pull-up. If the signal is sampled low,
the system is strapped to the “Top-Swap” mode (ICH2 will invert A16
for all cycles targeting FWH BIOS space). The status of this strap is
readable via the Top-Swap bit (bit 13, D31: F0, Offset D4h). Note that
software will not be able to clear the Top-Swap bit until the system is
rebooted without GNT[A]# being pulled down.
If this signal is sampled high (via an external pull-up to VCC1_8), the
normal hub interface buffer mode will be selected. If this signal is
sampled low (via an external pull-down), the enhanced hub interface
buffer mode will be selected.
See the specific platform design guide for resistor values and routing
guidelines for each hub interface mode.
The signal has a weak internal pull-up. If the signal is sampled low,
the system is strapped to the “No Reboot” mode (ICH2 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).
2-14
82801BA ICH2 and 82801BAM ICH2-M Datasheet