RG82855GMESL72L Datasheet, PDF (30/213 Pages) Intel Corporation – Intel® 855GM/855GME Chipset Graphics and Memory Controller Hub (GMCH)

Signal Descriptions
R
3.1
Host Interface Signals
Table 3. Host Interface Signal Descriptions
Signal Name
ADS#
BNR#
BPRI#
BREQ0#
CPURST#
DBSY#
DEFER#
DINV[3:0]#
DPSLP#
Type
I/O
AGTL+
I/O
AGTL+
O
AGTL+
I/O
AGTL+
O
AGTL+
I/O
AGTL+
O
AGTL+
I/O
AGTL+
I
CMOS
Description
Address Strobe: The system bus owner asserts ADS# to indicate the first of two
cycles of a request phase. The GMCH can assert this signal for snoop cycles and
interrupt messages.
Block Next Request: Used to block the current request bus owner from issuing a new
request. This signal is used to dynamically control the CPU bus pipeline depth.
Bus Priority Request: The GMCH is the only Priority Agent on the system bus. It
asserts this signal to obtain the ownership of the address bus. This signal has priority
over symmetric bus requests and will cause the current symmetric owner to stop
issuing new transactions unless the HLOCK# signal was asserted.
Bus Request 0#: The GMCH pulls the processor bus BREQ0# signal low during
CPURST#. The signal is sampled by the processor on the active-to-inactive transition
of CPURST#. The minimum setup time for this signal is 4 BCLKs. The minimum hold
time is 2 clocks and the maximum hold time is 20 BCLKs. BREQ0# should be tristated
after the hold time requirement has been satisfied.
During regular operation, the GMCH will use BREQ0# as an early indication for FSB
Address and Ctl input buffer and sense amp activation.
CPU Reset: The CPURST# pin is an output from the GMCH. The GMCH asserts
CPURST# while RESET# (PCIRST# from ICH4-M) is asserted and for approximately 1
ms after RESET# is deasserted. The CPURST# allows the processor to begin
execution in a known state.
Note that the ICH4-M must provide CPU strap set-up and hold-times around
CPURST#. This requires strict synchronization between GMCH, CPURST#
deassertion and ICH4-M driving the straps.
Data Bus Busy: Used by the data bus owner to hold the data bus for transfers
requiring more than one cycle.
Defer: GMCH will generate a deferred response as defined by the rules of the GMCH’s
Dynamic Defer policy. The GMCH will also use the DEFER# signal to indicate a CPU
retry response.
Dynamic Bus Inversion: Driven along with the HD[63:0]# signals. Indicates if the
associated signals are inverted or not. DINV[3:0]# are asserted such that the number
of data bits driven electrically low (low voltage) within the corresponding 16-bit group
never exceeds 8.
DINV# Data Bits
DINV[3]# HD[63:48]#
DINV[2]# HD[47:32]#
DINV[1]# HD[31:16]#
DINV[0]# HD[16:0]#
Deep Sleep #: This signal comes from the ICH4-M device, providing an indication of
C3 and C4 state control to the CPU. Deassertion of this signal is used as an early
indication for C3 and C4 wake up (to active HPLL). Note that this is a low-voltage
CMOS buffer operating on the FSB VTT power plane.
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Datasheet