Signal Description
R
Intel
®
82925X/82925XE MCH Datasheet 23
2.1 Host Interface Signals
Note: Unless otherwise noted, the voltage level for all signals in this interface is tied to the termination
voltage of the Host Bus (V
TT
).
Signal Name Type Description
HADS# I/O
GTL+
Address Strobe: The processor bus owner asserts HADS# to indicate the
first of two cycles of a request phase. The MCH can assert this signal for
snoop cycles and interrupt messages.
HBNR# I/O
GTL+
Block Next Request: This signal is used to block the current request bus
owner from issuing new requests. This signal is used to dynamically control
the processor bus pipeline depth.
HBPRI# O
GTL+
Priority Agent Bus Request: The MCH is the only Priority Agent on the
processor 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.
HBREQ0# I/O
GTL+
Bus Request 0: The MCH pulls the processor’s bus HBREQ0# signal low
during HCPURST#. The processor samples this signal on the active-to-
inactive transition of HCPURST#. The minimum setup time for this signal is
4 HCLKs. The minimum hold time is 2 clocks and the maximum hold time is
20 HCLKs. HBREQ0# should be tri-stated after the hold time requirement
has been satisfied.
HCPURST# O
GTL+
CPU Reset: The HCPURST# pin is an output from the MCH. The MCH
asserts HCPURST# while RSTIN# is asserted and for approximately 1 ms
after RSTIN# is de-asserted. The HCPURST# allows the processors to
begin execution in a known state.
Note that the Intel
®
ICH6 must provide processor frequency select strap set-
up and hold times around HCPURST#. This requires strict synchronization
between MCH HCPURST# de-assertion and the Intel® ICH6 driving the
straps.
HDBSY# I/O
GTL+
Data Bus Busy: This signal is used by the data bus owner to hold the data
bus for transfers requiring more than one cycle.
HDEFER# O
GTL+
Defer: Signals that the MCH will terminate the transaction currently being
snooped with either a deferred response or with a retry response.
HDINV[3:0]# I/O
GTL+
Dynamic Bus Inversion: Driven along with the HD[63:0] signals. Indicates
if the associated signals are inverted or not. HDINV[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.
HDINVx# Data Bits
HDINV3# HD[63:48]
HDINV2# HD[47:32]
HDINV1# HD[31:16]
HDINV0# HD[15:0]
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