62
Datasheet
Land Listing and Signal Descriptions
4.2
Alphabetical Signals Reference
Table 4-3. Signal Description (Sheet 1 of 9)
Name
Type
Description
A[35:3]#
Input/
Output
A[35:3]# (Address) define a 236-byte physical memory address space. In
sub-phase 1 of the address phase, these signals transmit the address of a
transaction. In sub-phase 2, these signals transmit transaction type
information. These signals must connect the appropriate pins/lands of all
agents on the processor FSB. 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]# signals to determine power-on configuration. See
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-MB
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]# signals. 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.
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/lands of all Celeron D processor in the 775-land package
FSB agents. The following table defines the coverage model of these
signals.
Signals
Associated Strobe
REQ[4:0]#, A[16:3]#
ADSTB0#
A[35:17]#
ADSTB1#
Request Signals
Subphase 1
Subphase 2
A[35:24]#
AP0#
AP1#
A[23:3]#
AP1#
AP0#
REQ[4:0]#
AP1#
AP0#