Signal Definitions
5 Signal Definitions
5.1
Signal Definitions
Table 5-1.
Signal Definitions (Sheet 1 of 8)
Name
Type
Description
Notes
36
A[35:3]#
I/O
A[35:3]# (Address) define a 2 -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 of all agents on the 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]#.
3
On the active-to-inactive transition of RESET#, the processors sample a subset of the
A[35:3]# lands to determine their power-on configuration. See Section 7.1.
A20M#
I
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.
2
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.
ADS#
I/O
I/O
ADS# (Address Strobe) is asserted to indicate the validity of the transaction address
on the A[35:3]# lands. 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. This signal must connect the
appropriate pins on all Dual-Core Intel Xeon Processor 5000 series FSB agents.
3
3
ADSTB[1:0]#
Address strobes are used to latch A[35:3]# and REQ[4:0]# on their rising and falling
edge. Strobes are associated with signals as shown below.
Signals
Associated Strobes
REQ[4:0], A[16:3]#
A[35:17]#
ADSTB0#
ADSTB1#
AP[1:0]#
I/O
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]# signals. 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 Dual-Core Intel Xeon
Processor 5000 series FSB agents. The following table defines the coverage model of
these signals.
3
Request Signals
Subphase 1
Subphase 2
A[35:24]#
A[23:3]#
AP0#
AP1#
AP1#
AP1#
AP0#
AP0#
REQ[4:0]#
BCLK[1:0]
I
The differential bus clock pair BCLK[1:0] (Bus Clock) determines the FSB frequency.
All processor FSB agents must receive these signals to drive their outputs and latch
their inputs.
3
All external timing parameters are specified with respect to the rising edge of BCLK0
crossing V
.
CROSS
Dual-Core Intel® Xeon® Processor 5000 Series Datasheet
61
INTEL [ INTEL ]
