82801BA Datasheet, PDF (128/498 Pages) Intel Corporation – Intel 82801BA I/O Controller Hub 2 (ICH2) and Intel 82801BAM I/O Controller Hub 2 Mobile

Functional Description
5.11 Processor Interface (D31:F0)
The ICH2 interfaces to the processor with a variety of signals:
• Standard outputs to the processor: A20M#, SMI#, NMI, INIT#, INTR, STPCLK#, IGNNE#,
CPUSLP#
• Standard input from the processor: FERR#
• For ICH2-M, Intel^® SpeedStep^TM Output to the processor: CPUPWRGOOD
Most ICH2 outputs to the processor use standard buffers. The ICH2 has a separate Vcc signal that
is pulled up at the system level to the processor voltage and thus, determines Voh for the outputs to
the processor. Note that this is different than previous generations of chips that have used open-
drain outputs. This new method saves up to 12 external pull-up resistors.
The ICH2 also handles the speed setting for the processor by holding specific signals at certain
states just prior to CPURST going inactive. This avoids the glue often required with other chipsets.
The ICH2 does not support the processor’s FRC mode.
5.11.1 Processor Interface Signals
This section describes each of the signals that interface between the ICH2 and the processor(s).
Note that the behavior of some signals may vary during processor reset, as the signals are used for
frequency strapping.
5.11.1.1
A20M#
The A20M# signal is active (low) when both of the following conditions are true:
• The ALT_A20_GATE bit (Bit 1 of PORT92 register) is a 0
• The A20GATE input signal is a 0
The A20GATE input signal is expected to be generated by the external microcontroller (KBC).
5.11.1.2
INIT#
The INIT# signal is active (driven low) based on any one of several events described in Table 5-31.
When any of these events occur, INIT# is driven low for 16 PCI clocks, then driven high.
Note: The 16-clock counter for INIT# assertion halts while STPCLK# is active. Therefore, if INIT# is
supposed to go active while STPCLK# is asserted, it actually goes active after STPCLK# goes
inactive.
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82801BA ICH2 and 82801BAM ICH2-M Datasheet