Revision 1.02 – April 12, 2007
S5920 – PCI Product: Pass-Thru Operation
Data Book
mation for the current PCI cycle. When the PCI bus
performs burst accesses, the APTA register is incre-
mented by the S5920 to reflect the address of the
current data phase. PTNUM[1:0] is used to determine
what region owns the current data access.
For PCI reads from the Add-On, the S5920 asserts the
Pass-Thru status signals to indicate to the Add-On that
data is required. The Add-On logic should write the
requested data into the Pass-Thru Read FIFO. The
S5920 will assert TRDY# to the PCI bus after the Add-
On logic has transferred data into the FIFO. As long as
data is in the FIFO, and PCI read data is still
requested, TRDY# will continue to be asserted. If the
Add-On cannot provide data quickly enough, the
S5920 signals a disconnect to the PCI bus. This
allows the PCI bus to perform other tasks, rather than
waiting for a slow target. The S5920 will prefetch data
if enabled.
For PCI writes to the Add-On, the S5920 transfers
data from the PCI bus into the Pass-Thru Write FIFO.
When the Pass-Thru write FIFO becomes not empty,
the S5920 asserts the Pass-Thru status signals to indi-
cate to the Add-On that data is present. The Add-On
logic will then read data from the FIFO. The S5920
continues accepting write data from the PCI initiator as
long as the 8x32 FIFO is not full.
Signal
Function
PTATN#
This output indicates a Pass-Thru access needs servicing.
This output indicates that the current Pass-Thru access is a PCI burst transfer or a single cycle transfer.
PTBURST# is deasserted immediately after the second to last burst data has been transferred on the PCI
side. PTBURST# is also active during prefetch cycles.
PTBURST#
PTNUM[1:0] These outputs indicate which Pass-Thru region decoded the PCI address.
These outputs indicate which data bytes are valid (PCI writes), or requested (PCI reads). See timing dia-
PTBE[3:0]#
PTWR
grams for further details. PTBE0# = 0 Byte 0 is valid, PTBE1# = 0 Byte 1 is valid, PTBE# = 0 Byte 2 is valid,
PTBE3# = 0 Byte 3 is valid.
This output indicates if the Pass-Thru access is a PCI read or a write.
When asserted, this pin drives the Pass-Thru Address Register contents onto the Add-On data bus. This
input enables the DQ[31:0] data bus to become active immediately. There is NO pipeline delay from PTADR#
to DQ, as there is from RD# to DQ. As result, this is an asynchronous input.
PTADR#
In Passive mode, this input indicates the current Pass-Thru transfer has been has been completed by the
Add-On. In Active mode, this input indicates that wait states are to be inserted for the next transfer.
PTRDY#
ADCLK
Input Add-On clock (to synchronize Pass-Thru data register accesses).
Pass-Thru Status/Control Signals
ated by the PCI bus. The Pass-Thru interface is
designed to allow Add-On logic to function without
knowledge of PCI bus activity. Add-On logic only
needs to react to the Pass-Thru status signals. The
S5920 PCI device independently interacts with the
PCI initiator to control data flow between the devices.
The S5920 Pass-Thru registers are accessed using
the Add-On register access pins. The Pass-Thru
Address Register (APTA) can, optionally, be accessed
using a single, direct access input, PTADR#. Pass-
Thru cycle status indicators are provided to control
Add-On logic based on the type of Pass-Thru access
occurring (single cycle, burst, etc.). The signals in the
table above are provided for Pass-Thru operation:
The following sections describe the PCI and Add-On
bus interfaces. The PCI interface description provides
a basic overview of how the S5920 interacts with the
PCI bus, and may be useful in system debugging. The
Add-On interface description indicates functions
required by Add-On logic and details the Pass-Thru
handshaking protocol.
BUS INTERFACE
The Pass-Thru data channel allows PCI initiators to
read or write to resources on the Add-On bus. A PCI
initiator may access the Add-On with single data
phase cycles or multiple data phase bursts. The Add-
On interface implements Pass-Thru status and control
signals used by logic to complete data transfers initi-
PCI Bus Interface
The S5920 device examines all PCI bus cycle
addresses. If the address associated with the current
AMCC Confidential and Proprietary
DS1596
122
AMCC [ APPLIED MICRO CIRCUITS CORPORATION ]
