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Signal Description
2-8
82801AA and 82801AB Datasheet
2.9
Processor Interface
Table 2-9. Processor Interface Signals
Name
Type
Description
A20M#
OD
Mask A20:
A20M# will go active based on either setting the appropriate bit in the Port
92h register, or based on the A20GATE input being active.
Speed Strap:
During the reset sequence, ICH drives A20M# high if the corresponding
bit is set in the FREQ_STRP register.
CPUSLP#
OD
Processor Sleep:
This signal puts the processor into a state that saves substantial
power compared to Stop-Grant state. However, during that time, no snoops occur. The
ICH can optionally assert the processor SLP# signal when going to the S1 state.
FERR#
I
Numeric Coprocessor Error:
This signal is tied to the coprocessor error signal on the
processor. IGNNE# is only used if the ICH coprocessor error reporting function is
enabled in the General Control Register (Device 31:Function 0, Offset D0, bit 13). If
FERR# is asserted, the ICH generates an internal IRQ13 to its interrupt controller unit. It
is also used to gate the IGNNE# signal to ensure that IGNNE# is not asserted to the
processor unless FERR# is active. FERR# requires an external weak pull-up to ensure
a high level when the coprocessor error function is disabled.
IGNNE#
OD
Ignore Numeric Error:
This signal is connected to the ignore error pin on the
processor. IGNNE# is only used if the ICH coprocessor error reporting function is
enabled in the General Control Register (Device 31:Function 0, Offset D0, bit 13). If
FERR# is active, indicating a coprocessor error, a write to the Coprocessor Error
Register (F0h) causes the IGNNE# to be asserted. IGNNE# remains asserted until
FERR# is negated. If FERR# is not asserted when the Coprocessor Error Register is
written, the IGNNE# signal is not asserted.
Speed Strap:
During the reset sequence, ICH drives IGNNE# high if the corresponding
bit is set in the FREQ_STRP register.
INIT#
OD
Initialization:
INIT# is asserted by the ICH for 16 PCI clocks to reset the processor.
The 82810AA can be configured to support Processor BIST. In that case, INIT# will
be active when PCIRST# is active.
INTR
OD
Processor Interrupt:
INTR is released by the ICH to signal the processor that an
interrupt request is pending and needs to be serviced. It is an asynchronous output and
normally driven low.
Speed Strap:
During the reset sequence, ICH drives INTR high if the corresponding bit
is set in the FREQ_STRP register.
NMI
OD
Non-Maskable Interrupt:
NMI is used to force a non-maskable interrupt to the
processor. The ICH can generate an NMI when either SERR# or IOCHK# is asserted.
The processor detects an NMI when it detects a rising edge on NMI. NMI is reset by
setting the corresponding NMI source enable/disable bit in the NMI Status and Control
Register.
Speed Strap:
During the reset sequence, ICH drives NMI high if the corresponding bit
is set in the FREQ_STRP register.
SMI#
OD
System Management Interrupt:
SMI# is an active low output synchronous to PCICLK.
It is asserted by the ICH in response to one of many enabled hardware or software
events.
STPCLK#
OD
Stop Clock Request:
STPCLK# is an active low output synchronous to PCICLK. It is
asserted by the ICH in response to one of many hardware or software events. When the
processor samples STPCLK# asserted, it responds by stopping its internal clock.
STPCLK# is floated during PCIRST#.
RCIN#
I
Keyboard Controller Reset Processor:
The keyboard controller can generate INIT#
to the processor. This saves the external OR gate with the ICH’s other sources of INIT#.
When the ICH detects the assertion of this signal, INIT# is generated for 16 PCI clocks.
A20GATE
I
A20 Gate:
From the keyboard controller. Acts as an alternative method to force the
A20M# signal active. Saves the external OR gate needed with various other PCIsets.