PENTIUM II XEON PROCESSOR AT 400 AND 450 MHZ
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12/15/98 5:14 PM 24377002.doc
APPENDIX A
9.0.
APPENDIX
This appendix provides an alphabetical listing of all
Pentium II Xeon processor signals and tables that
summarize the signals by direction: output, input, and
I/O.
9.1.
Alphabetical Signals Reference
This section provides an alphabetical listing of all
Pentium II Xeon processor signals.
9.1.1.
A[35:03]# (I/O)
The A[35:3]# (Address) signals define a 2
36
-byte
physical memory address space. When ADS# is
active, these pins transmit the address of a
transaction; when ADS# is inactive, these pins
transmit transaction type information. These signals
must connect the appropriate pins of all agents on
the Pentium II Xeon processor system bus. The
A[35:24]# signals are parity-protected by the AP1#
parity signal, and the A[23:03]# signals are parity-
protected by the AP0# parity signal.
On the active-to-inactive transition of RESET#, the
processors sample the A[35:03]# pins to determine
their power-on configuration. See the Pentium
II
Processor Developer’s Manualfor details.
9.1.2.
A20M# (I)
If the A20M# (Address-20 Mask) input signal is
asserted, the Pentium II Xeon processor masks
physical address bit 20 (A20#) before looking up a
line in any internal cache and before driving a
read/write transaction on the bus. Asserting A20M#
emulates the 8086 processor’s address wrap-around
at the 1-Mbyte boundary. Assertion of A20M# is only
supported in real mode.
A20M# is an asynchronous signal. However, to
ensure recognition of this signal following an I/O write
instruction, it must be valid along with the TRDY#
assertion of the corresponding I/O Write bus
transaction.
During active RESET#, each processor begins
sampling the A20M#, IGNNE#, and LINT[1:0] values
to determine the ratio of core-clock frequency to bus-
clock frequency. See Table 1. On the active-to-
inactive transition of RESET#, each processor
latches these signals and freezes the frequency ratio
internally. System logic must then release these
signals for normal operation.
9.1.3.
ADS# (I/O)
The ADS# (Address Strobe) signal is asserted to
indicate the validity of the transaction address on the
A[35:03]# pins. All bus agents observe the ADS#
activation to begin parity
checking, address decode, internal snoop, or
deferred reply ID match operations associated with
the new transaction. This signal must connect the
appropriate pins on all Pentium II Xeon processor
system bus agents.
checking,
protocol
9.1.4.
AERR# (I/O)
The AERR# (Address Parity Error) signal is
observed and driven by all Pentium II Xeon
processor system bus agents, and if used, must
connect the appropriate pins on all Pentium II Xeon
processor system bus agents. AERR# observation is
optionally enabled during power-on configuration; if
enabled, a valid assertion of AERR# aborts the
current transaction.
If AERR# observation is disabled during power-on
configuration, a central agent may handle an
assertion of AERR# as appropriate to the Machine
Check Architecture (MCA) of the system.
9.1.5.
AP[1:0]# (I/O)
The AP[1:0]# (Address Parity) signals are driven by
the request initiator along with ADS#, A[35:03]#,
REQ[4:0]#, and RP#. AP1# covers A[35:24]#, and
AP0# covers A[23:03]#. A correct parity signal is high
if an even number of covered signals are low and low
if an odd number of covered signals are low. This
allows parity to be high when all the covered signals
are high. AP[1:0]# should connect the appropriate