82870P2P64H2 Datasheet, PDF (150/217 Pages) –

Functional Description
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4.3.3
4.3.3.1
Single Slot Mode PCI Bus Effects
When in single slot mode, the PCI bus operates differently when no cards are plugged into the
system. This is because in a single-slot environment, no isolation logic (Q-switches) is on the
board. This section lists those differences.
Driving Bus To Ground When PCI Card is Disconnected
When in single slot mode, all PCI signals are to be driven to ground when the PCI card is
disconnected. The signals that must be driven to ground are the following:
• PxAD[63:0], PxC/BE[7:0]#, PxPAR, PxPAR64, PxREQ64#, PxACK64#
• PxFRAME#, PxIRDY#, PxTRDY#, PxSTOP#, PxDEVSEL#, PxLOCK#
• PxGNT[5:0]#
• PxREQ[5:0]#
• PxPERR#, PxSERR#
• PxPCLKO[5:0] (Only driven to ground if enabled through the bridge – otherwise these
outputs remain high. PxPCLKO6 is not driven to ground because it is the connected back to
PxPCLKI).
• HxRESETA# (Slot specific reset from parallel hot plug control signal interface).
• PxIRQ[7:0]
These signals will be driven back to their normal PCI levels at various times in the clock
connection process. When a card is reconnected to the bus, it follows the following algorithm:
• Power is applied to the card. This does not affect any of the PCI signals that are now being
driven to ground.
• After a variable period of time, the clock is connected to the card. When this occurs,
PxPCLKO[5:0] will no longer be driven to ground, but will toggle normally (assuming that
BIOS has not disabled that particular PxPCLKO pin). In hot plug terms, this is the equivalent
of the “CLKEN#” signal.
• After another variable period of time, the bus is connected to the card. When this occurs, The
remaining signals listed above which were driven to ground will be driven to new signal
values, except for the slot reset, which will continue to be driven to ground. The new signal
values are listed below:
 PxAD[63:0], PxC/BE[7:0]#, PxPAR, PxPAR64: These signals are driven to some value
(low or high) depending on internal state. (PAR and PAR64 are driven one PCI-X clock
after the other lines are driven.)
 PxREQ64#: This signal is driven low to indicate to card that it is connected to a 64-bit
wide data bus.
 PxFRAME#, PxIRDY#, PxLOCK#, PxREQ[2:0]#, PxGNT[2:0]#, PxPERR#, PxSERR#,
PxACK64#: These signals are driven high for one PCI-X clock, then tri-stated.
 PxTRDY#, PxSTOP#, PxDEVSEL#: In PCI mode, these signals are driven high for one
PCI clock, then tri-stated. In PCI-X mode, these signals are driven to the PCI-X
initialization pattern associated with the current PCI-X bus speed.
 PxIRQ[7:0]: Tri-states.
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Intel^® 82870P2 P64H2 Datasheet