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PASS-THRU OVERVIEW
S5933
Clock 2: SELECT#, byte enable, and the address
inputs remain driven to read the Pass-Thru
Data Register at offset 2Ch. PTBURST# is
asserted by the S5933, indicating the
current Pass-Thru read is a burst.
Clock 3: WR# asserted at the rising edge of clock 3
writes DATA 1 into the S5933. PTRDY#
asserted at the rising edge of clock 3
completes the current data phase.
Clock 4: Add-On logic drives DATA 2 on the Add-On
bus, but PTRDY# deasserted at the rising edge
of clock 4 extends the current data phase.
Clock 5: WR# asserted at the rising edge of clock 5
writes DATA 2 into the S5933. PTRDY#
asserted at the rising edge of clock 5
completes the current data phase.
Clock 6: Add-On logic drives DATA 3 on the Add-On
bus, but PTRDY# deasserted at the rising edge
of clock 6 extends the current data phase.
Clock 7: WR# asserted at the rising edge of clock 7
writes DATA 3 into the S5933. PTRDY#
asserted at the rising edge of clock 7
completes the current data phase. On the
PCI bus, IRDY# has been deasserted,
causing PTATN# to be deasserted. This is
how a PCI initiator adds wait states, if it
cannot read data quickly enough.
Clock 8: PTATN# remains deasserted at the rising
edge of clock 8. The Add-On cannot write
DATA 4 until PTATN# is asserted. Add-On
logic continues to drive DATA 4 on the
Add-On bus. PTATN# is reasserted during
the cycle, indicating the PCI initiator is
done adding wait states.
Clock 9: WR# asserted at the rising edge of clock 9
writes DATA 4 into the S5933. PTRDY#
asserted at the rising edge of clock 9
completes the current data phase.
Clock 10: Add-On logic drives DATA 5 on the Add-On
bus, but PTRDY# deasserted at the rising edge
of clock 10 extends the current data phase.
Clock 11: PTATN# remains deasserted at the rising
edge of clock 11. The Add-On does not
have to write DATA 5 until PTATN# is
asserted. Add-On logic continues to drive
DATA 5 on the Add-On bus. PTATN# is
reasserted during the cycle, indicating the
PCI initiator is done adding wait states.
Clock 12: PTRDY# asserted at the rising edge of
clock 12 completes the final data phase.
Any data written into the Pass-Thru data
register is not required and is never passed
to the PCI interface (as PTRDY# is not
asserted at the rising edge of clock 13).
Clock 13: PTATN# and PTBURST# deasserted at
the rising edge of clock 13 indicates the
Pass-Thru access is complete. The S5933
can accept new Pass-Thru accesses from
the PCI bus at clock 14.
Add-On Pass-Thru Disconnect Operation
Slow PCI targets are prevented from degrading PCI
bus performance. The PCI specification allows only
16 clocks for a target to respond before it must re-
quest a retry on single data phase accesses. For
burst accesses, the first data phase is allowed 16
clocks to complete, all subsequent data phases are
allowed 8 clocks each. This requirement allows other
PCI initiators to use the bus while the target request-
ing the retry completes the original access.
Figure 8 shows the conditions that cause the S5933
to request a retry from a PCI initiator on the first data
phase of a PCI read operation. FRAME# is asserted
during the rising edge of PCI clock 1. From this point,
Figure 8. Target Requested Retry on the First PCI Data Phase
18
17
16
15
4
3
2
1
17
16
15
14
3
2
1
PCICLK
FRAME#
STOP#
BPCLK
PTATN#
PTRDY#
PTRDY# must be asserted by
this time to present disconnecting
PTRDY# asserted too late so
S593X disconnects (asserts STOP#)