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8170 N/B MAINTENANCE
5. Pin Descriptions of Major Components
5.1 Pentium 4(Willamette/Northwood) mFC-PGA2 478 pin
Name Type Description
A[35:3]#
Input/
Output
A[35:3]# (Address) define a 2
36 -byte physical memory address
space. In sub-phase 1 of the address phase, these pins transmit the
address of a transaction. In sub-phase 2, these pins transmit
transaction type information. These signals
must connect the appropriate pins of all agents on the Pentium 4
processor in the 478-pin package system bus. A[35:3]# are
protected by parity signals AP[1:0]#. A[35:3]# are source
synchronous signals and are latched into the receiving buffers by
ADSTB[1:0]#. On the active-to-inactive transition of RESET#, the
processor samples a subset of the A[35:3]# pins to determine
power-on configuration.
A20M#
Input If A20M# (Address-20 Mask) is asserted, the 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 Input/Output write instruction, it must be
valid along with the TRDY# assertion of the corresponding
Input/Output Write bus transaction.
ADS#
Input/
Output
ADS# (Address Strobe) is asserted to indicate the validity of the
transaction address on the A[35:3]# and REQ[4:0]# pins. All bus
agents observe the ADS# activation to begin parity checking,
protocol checking, address decode, internal snoop, or deferred reply
ID match operations associated with the new transaction.
ADSTB[1:0]#
Input/
Output
Address strobes are used to latch A[35:3]# and REQ[4:0]# on their
rising and falling edges. Strobes are associated with signals as
shown below.
Signals Associated Strobe
REQ[4:0]#, A[16:3]# ADSTB0#
A[35:17]# ADSTB1#
Name Type Description
AP[1:0]#
Input/
Output
AP[1:0]# (Address Parity) are driven by the request initiator along
with ADS#,A[35:3]#, and the transaction type on the REQ[4:0]#. 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 pins of all Pentium 4
processor in the 478-pin package system bus agents. The following
table defines
Request Signals subphase 1 subphase 2
A[35:24]# AP0# AP1#
A[23:3]# AP1# AP0#
REQ[4:0]# AP1# AP0#
BCLK[1:0]
Input The differential pair BCLK (Bus Clock) determines the system bus
frequency. All processor system bus agents must receive these
signals to drive their outputs and latch their inputs.
All external timing parameters are specified with respect to the
rising edge of BCLK0 crossing V CROSS .
BINIT#
Input/
Output
BINIT# (Bus Initialization) may be observed and driven by all
processor system bus agents and if used, must connect the
appropriate pins of all such agents. If the BINIT# driver is enabled
during power-on configuration, BINIT# is asserted
to signal any bus condition that prevents reliable future operation.
If BINIT# observation is enabled during power-on configuration,
and BINIT# is sampled asserted, symmetric agents reset their bus
LOCK# activity and bus request arbitration state machines. The bus
agents do not reset their IOQ and transaction tracking state
machines upon observation of BINIT# activation. Once the BINIT#
assertion has been observed, the bus agents will re-arbitrate for the
system bus and attempt completion of their bus queue and IOQ
entries.
If BINIT# observation is disabled during power-on configuration, a
central agent may handle an assertion of BINIT# as appropriate to
the error handling architecture of the system.
BNR#
Input/
Output
BNR# (Block Next Request) is used to assert a bus stall by any bus
agent who is unable to accept new bus transactions. During a bus
stall, the current bus owner cannot issue any new transactions.