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Land Listing and Signal Descriptions

Datasheet

4.2

Alphabetical Signals Reference

Table 25.

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 Section 6.1 for more details.

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

processor 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#

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