Pin Listing and Signal Definitions
5.2
Alphabetical Signals Reference
Table 37. Signal Description (Page 1 of 8)
Name
Type
Description
A[35:3]# (Address) define a 236-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 Mobile Intel Pentium 4
Processor-M 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]#.
Input/
Output
A[35:3]#
On the active-to-inactive transition of RESET#, the processor samples a subset of
the A[35:3]# pins to determine power-on configuration. See Section 7.1 for more
details.
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#
ADS#
Input
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# (Address Strobe) is asserted to indicate the validity of the transaction
Input/ address on the A[35:3]# and REQ[4:0]# pins. All bus agents observe the ADS#
Output activation to begin parity checking, protocol checking, address decode, internal
snoop, or deferred reply ID match operations associated with the new transaction.
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.
Input/
Output
Signals
Associated Strobe
ADSTB[1:0]#
REQ[4:0]#, A[16:3]#
A[35:17]#
ADSTB0#
ADSTB1#
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 Mobile Intel Pentium 4
Processor-M system bus agents. The following table defines the coverage model of
these signals.
Input/
Output
AP[1:0]#
BCLK[1:0]
Request Signals
A[35:24]#
subphase 1
AP0#
subphase 2
AP1#
A[23:3]#
AP1#
AP0#
REQ[4:0]#
AP1#
AP0#
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.
Input
All external timing parameters are specified with respect to the rising edge of
BCLK0 crossing VCROSS
.
Mobile Intel Pentium 4 Processor-M Datasheet
81
INTEL [ INTEL ]
