
SECTION 3
PCI 9080
FUNCTIONAL DESCRIPTION
PLX Technology, Inc., 1997
Page 24
Version 1.02
case when the Local Bus Latency Timer is enabled and
expires. (Refer to Figure 3-11 and Figure 3-12.)
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; -.
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&(); <);
-.
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Figure 3-11. Direct Slave Write
For direct slave writes, the PCI (Master) writes data to
the local bus (slave). Direct Slave is the “Command from
the PCI host,” which has the highest priority. Direct
Slave or Direct Master pre-empts DMA; however, Direct
Slave does not pre-empt Direct Master (refer to Section
3.6.2.3.1, “Backoff”).
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>
; -
.
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);
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-.
Figure 3-12. Direct Slave Read
For direct slave reads, the PCI (Master) reads data from
the local bus (Slave).
PCI 9080 supports on-the-fly Endian conversion for
Space 0, Space 1, and expansion ROM space. The local
bus can be Big/Little Endian by either using the
BIGEND# input pin or the programmable internal register
configuration. When BIGEND# is asserted, it overwrites
the internal register configuration.
Note:
PCI bus is always Little Endian.
3.6.2.2 PCI to Local Address Mapping
Note:
Not applicable if I
2
O mode.
Three local address spaces—Space 0, Space 1, and
expansion ROM—are accessible from the PCI bus. Each
is defined by a set of three registers:
Local Address Range
Local Base Address
PCI Base Address
A fourth register, Bus Region Descriptor Register for PCI
to local accesses, defines the local bus characteristics
for both regions. (Refer to Figure 3-13.)
3.6.2.2.1 Byte Enables
LBE[3:0]# (pins 139-142) are encoded based on the
configured bus width, as follows:
32-Bit Bus
—For a 32-bit bus, the four byte enables
indicate which of the four bytes are active during a data
cycle.
BE3# Byte Enable 3—LD[31:24]
BE2# Byte Enable 2—LD[23:16]
BE1# Byte Enable 1—LD[15:8]
BE0# Byte Enable 0—LD[7:0]
16-Bit Bus
—For a 16-bit bus, BE3#, BE1# and BE0#
are encoded to provide BHE#, LA1, and BLE#,
respectively.
BE3# Byte High Enable (BHE#)—LD[15:8]
BE2# not used
BE1# Address bit 1 (LA1)
BE0# Byte Low Enable (BLE#)— LD[7:0]
8-Bit Bus
—For an 8-bit bus, BE1# and BE0# are
encoded to provide LA1 and LA0, respectively.
BE3# not used
BE2# not used
BE1# Address bit 1 (LA1)
BE0# Address bit 0 (LA0)
Each PCI to Local Address space is defined as part of
reset initialization as described in the next section.