Signal Description
Software must choose the in-band reset time period comprehending potential mode switches that
can happen on the PCI-X bus and the associated time period required to settle the voltage and meet
the minimum PxPCIRST# timing requirements. This could be up to or beyond 320 ms.
2.17.2.4
Software PCI Reset (or SBR - Secondary Bus Reset)
Commonly referred to as the Secondary Bus Reset (SBR), this reset is initiated by a write to the
bridge control register and resets only the particular PCI segment. This reset can be used for
various reasons in including recovering from error conditions on the secondary bus, redoing
enumeration, changing the operating frequency of the bus (33/66/100/133 MHz), changing the
operating mode of the bus (PCI or PCI-X), etc. This reset is synchronous to the PCI clock domain
in which it is used. SBR is strictly restricted to the particular PCI segment and affects neither the
other PCI segment nor the rest of the Intel® 6700PXH 64-bit PCI Hub logic. Writes to the bridge
control register with a new frequency etc., will have no effect until the SBR happens. The power up
frequency of the PCI bus is shown in Table 2-36. When hot plug is enabled the bus always powers
up in PCI 33 MHz mode. With hot plug disabled the frequency depends on the PxM66EN,
Px133EN, PxPCIXCAP and HPx_SOC/PxMODE2 pins.
Table 2-36. Power-On Frequency of Intel® 6700PXH 64-bit PCI Hub
PCI
Capability
PCIXCAP
(on the card)
PCI-X Capability
M66EN
133EN
33 MHz
66 MHz
33 MHz
66 MHz
33 MHz
66 MHz
33 MHz
66 MHz
Not Capable
GND
X
X
X
X
GND
GND
Not Capable
1 k-10 kΩ pull-up
GND
PCI-X 66 MHz
PCI-X 66 MHz
PCI-X 100 MHz
PCI-X 100 MHz
PCI-X 133 MHz
PCI-X 133 MHz
Pull-down 10 kΩ ±5%
No Connect
GND
Pull-down 10 kΩ ±5%
Pull-down
Pull-down
Pull-up
0.01 µF capacitor to GND
0.01 µF capacitor to GND
0.01 µF capacitor to GND
0.01 µF capacitor to GND
No Connect
GND
No Connect
Pull-up
2.17.2.5
Hot Plug Reset
This reset is initiated by a write to the hot plug command register with the change frequency
command. Note that a write to this register might do any of the following:
• Change the frequency (33/66/100/133 MHz).
• Change the mode (PCI or PCI-X).
• Change nothing but rewrite the present settings.
Any write (doing any of the three above) will cause a reset of the particular PCI segment to reset.
This reset is asynchronous by nature to the PCI clock as the hot plug logic runs off of an internal
clock that ‘may’ be asynchronous to the PCI clock. This reset will cause the any newly written
frequency or PCI mode information to take effect. The Intel® 6700PXH 64-bit PCI Hub will
support all changes in mode because of hot plug events including switching from PCI to PCI-X
protocols or changing the frequency.
Intel® 6700PXH 64-bit PCI Hub Datasheet
73
INTEL [ INTEL ]
