Package Mechanical Specifications and Pin Information
70
Datasheet
4.2
Alphabetical Signals Reference
Table 4-5. Signal Description (Sheet 1 of 7)
Name
Type
Description
A[31:3]#
Input/
Output
A[31:3]# (Address) define a 2
32
-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 both agents on the Intel
®
Pentium
®
M
Processor FSB. A[31:3]# are source synchronous signals and are latched into
the receiving buffers by ADSTB[1:0]#. Address signals are used as straps which
are sampled before RESET# is deasserted.
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[31:3]# 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[31:3]# and REQ[4:0]# on their rising and
falling edges. Strobes are associated with signals as shown below.
BCLK[1:0]
Input
The differential pair BCLK (Bus Clock) determines the FSB frequency. All FSB
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
.
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.
BPM[2:0]#
BPM[3]
Output
Input/
Output
BPM[3:0]# (Breakpoint Monitor) are breakpoint and performance monitor
signals. They are outputs from the processor which indicate the status of
breakpoints and programmable counters used for monitoring processor
performance. BPM[3:0]# should connect the appropriate pins of all Intel
®
Pentium
®
M FSB agents.This includes debug or performance monitoring tools.
Please refer to the platform design guides for
more detailed information.
BPRI#
Input
BPRI# (Bus Priority Request) is used to arbitrate for ownership of the FSB. It
must connect the appropriate pins of both FSB agents. Observing BPRI# active
(as asserted by the priority agent) causes the other agent to stop issuing new
requests, unless such requests are part of an ongoing locked operation. The
priority agent keeps BPRI# asserted until all of its requests are completed, then
releases the bus by deasserting BPRI#.
BR0#
Input/
Output
BR0# is used by the processor to request the bus. The arbitration is done
between Intel
®
Pentium
®
M (Symmetric Agent) and Intel 855 chipset family
MCH-M (High Priority Agent).
Signals
Associated Strobe
REQ[4:0]#, A[16:3]#
ADSTB[0]#
A[31:17]#
ADSTB[1]#
