Digi NS9750 - Manual (Page 481)

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P C I - t o - A H B B r i d g e
The internal PCI arbiter is selected when the
RTCK
pin is set to 1 during powerup.
Because the
RTCK
pad has a weak internal pullup, no external components are
required to select the internal PCI arbiter.
Figure 73 shows how NS9750 is connected to the PCI bus for a typical application
using an external PCI bus arbiter, and where the NS9750 does not provide the PCI
central resource functions (see "PCI central resource functions" on page 458).
RTCK
is
pulled low by an external resistor to configure NS9750 to use an external arbiter. The
REQ0#/GNT0# pair for the external PCI arbiter is multiplexed out on the GNT1#/
REQ1# pins — GNT1# to REQ0# and REQ1# to GNT0#.
Figure 73: System connections to NS9750 — External arbiter and central resources
NS9750
REQ1#
REQ2#
REQ3#
GNT3#
GNT2#
GNT1#
AD[31:0]
PC
I BU
S
Control
AD[12]
IDSEL
PCI INTERRUPT
INTA#
PCI CLK
OUT
PCI CLK
IN
External
PCI Arbiter
REQ0# GNT0#
GNT1# REQ1#
RTCK
Pull down to
configure for external
arbiter
PCI_CENTRAL_RSC_n
VCC
RST#
SERR#
Pull up to
configure for external
central resource