2. PCI Interface
33
PowerSpan II User Manual
80A1010_MA001_09
Integrated Device Technology
www.idt.com
When P1_64EN# is at a logic low, and PWRUP_P1_R64_EN is selected, P1_REQ64# is asserted low
during reset. The status of PWRUP_P1_R64_EN is reflected in the P1_R64_EN bit in the
Control and Status Register” on page 324
.
2.1.2.2
PowerSpan II in non-Hot Swap and PCI Peripheral Applications
The PCI-1 Interface supports the following mechanisms for determining the width of the PCI-1
datapath:
•
sampling P1_REQ64# at the negation of P1_RST#
•
logic level on P1_64EN#
In non-Hot Swap applications, the P1_64EN# signal must be pulled high in order to enable sampling of
P1_REQ64# to determine the width of the data path. The result of the sampling of P1_REQ64# is or’d
with the logic level on P1_64EN# to determine data path width (see
).
2.1.2.3
PowerSpan II in Hot Swap Applications
In Hot Swap applications the P1_64EN# signal is the only signal sampled to indicate the PCI data
width. The following scenarios can be used for determining the proper implementation of the
P1_REQ64# and P1_64EN# signals:
•
PCI bus is currently a 32-bit slot and the Hot Swap board is 64-bit capable. In this case,
P1_REQ64# is pulled up in the slot and P1_64EN# is OPEN and the card will initialize in 32-bit
mode.
•
PCI bus is currently a 32-bit slot and the Hot Swap board is 32-bit capable. In this case,
P1_REQ64# is not sampled and P1_64EN# does not exist on the board so initialization would be
32-bit mode.
This feature must only be used in systems where PowerSpan II controls both P1_REQ64#
and P1_RST#. In this scenario, PowerSpan II is the Central Resource in the system and can
ensure that timing parameters are satisfied.
Table 3: Signals Involved in PCI Data Width Determination
Signal
Result
P1_REQ64#
P1_64EN#
0
0
64-bit bus
1
0
64-bit bus
0
1
64-bit bus
1
1
32-bit bus