SECTION 2
PCI 9080
BUS OPERATION
PLX Technology, Inc., 1997
Page 7
Version 1.02
REQ# for a minimum of two PCI clocks between bus
master ownership that includes a target disconnect.
The Direct Master Write Delay bits (bits [15:14]) of the
DMPBAM
Register
(PCI:28h)(LOC:A8h)
programmed to delay the PCI 9080’s assertion of the
PCI REQ# signal during a Direct Master write cycle. This
register can be programmed to wait 0, 4, 8, or 16 PCI
bus clocks after the PCI 9080 has received its first write
data from the local master and is ready to begin the PCI
write transaction. This feature is useful in applications
where the local master is bursting and the local bus
clock is slower than the PCI bus clock. This allows write
data to accumulate in the PCI 9080’s Direct Master Write
FIFO, which provides for better PCI bus utilization.
can
be
2.2 LOCAL BUS CYCLES
PCI 9080 connects a PCI host bus to several local
processor bus types, as listed in Table 2-6. It operates in
one of three modes, selected through mode pins 9 and
10, corresponding to three bus types—C, J, and S.
Table 2-6. Local Processor Bus Types
Bit 9
Bit 10
Mode
Bus Type
0
0
C
32-bit nonmultiplexed
0
1
J
32-bit multiplexed
1
0
S
16-bit multiplexed
1
1
Reserved
—
2.2.1 Local Bus Arbitration
When PCI 9080 owns the local bus, both its LHOLD
output and LHOLDA input are asserted. When PCI 9080
samples BREQ asserted during a DMA transfer or
Direct Slave write transfer, it gives up the local bus
within two Lword transfers by de-asserting LHOLD and
floating its local bus outputs if BREQ is gated or
disabled, or if gating is enabled and the Local Bus
Latency Timer expires. The Local Arbiter can now grant
the local bus to another local master. After PCI 9080
samples that its LHOLDA is de-asserted and its local
pause timer is zero, it re-asserts LHOLD to request the
local bus. When the PCI 9080 receives LHOLDA, it
drives the bus and continues from where it left off.
2.2.2 Local Bus Direct Master
Local bus cycles can be continuous single or burst
cycles (programmable by way of the PCI 9080 internal
registers). As a local bus target, PCI 9080 allows access
to PCI 9080 internal registers and PCI bus.
In C and J modes, local bus direct master accesses to
the PCI 9080 must be for a 32 bit nonpipelined bus. In S
mode, local bus direct master accesses to the PCI 9080
must be for a 16 bit nonpipelined bus.
2.2.3 Local Bus Direct Slave
PCI Bus Master read/write to local bus (PCI 9080 is a
PCI bus target and local bus master).
2.2.3.1 Ready/Wait State Control
!
"!#
#! $ #
%
"
&&'
(
$
#
!
)
*!
!! !+
!
,
!
,'
-"%!.
! "
/
)
Figure 2-1. Wait States
If READYi# input is disabled, external READYi# input
has no effect on wait states for a local access. Wait
states between data cycles are generated internally by a
wait state counter. Wait state counter is initialized with its
configuration register value at the start of each data
access.
If READYi# is enabled, READYi# has no effect until the
wait state counter is 0. READYi# then controls the
number of additional wait states.
BTERM# input is not sampled until the wait state counter
is 0. BTERM# overrides READYi# when BTERM# is
asserted.
2.2.3.1.1 Wait State—Local Side
With Direct Master mode and accessing PCI 9080
registers (PCI 9080 local as slave):
PCI 9080 generates wait states with READYo#
Local processor generates wait states with WAITI#