S5935TFC AMCC [Applied Micro Circuits Corporation], S5935TFC Datasheet - Page 150

• Manufacturer Part Number: S5935TFC
• Description: PCI Product
• Manufacturer: AMCC [Applied Micro Circuits Corporation]

S5935 – PCI Product
Thru Address Register (APTA), and a Pass-Thru Data
Register (APTD). These registers are connected to
both the PCI bus interface and the Add-On bus inter-
face. This allows a PCI initiator to perform Pass-Thru
writes (data transferred from the PCI bus to the Add-
On bus) or Pass-Thru reads (PCI bus requests data
from the Add-On bus). The S5935 Pass-Thru interface
supports both single cycle (one data phase) and burst
accesses (multiple data phases).
Pass-Thru Transfers
Data transfers between the PCI bus and the Add-On
using the Pass-Thru interface are implemented with a
handshaking scheme. If the PCI bus writes to an
S5935 Pass-Thru region, Add-On logic must read the
data from the S5935 and store it on the Add-On. If the
PCI bus reads from a Pass-Thru region, Add-On logic
must write data to the S5935.
Some applications may require that an address be
passed to the Add-On for Pass-Thru accesses. For
example, a 4 Kbyte Pass-Thru region on the PCI bus
may correspond to a 4 Kbyte block of SRAM on the
Add-On card. If a PCI initiator accessed this region,
the Add-On would need to know the offset within the
memory device to access. The Pass-Thru Address
Register (APTA) allows the Add-On to access address
information for the current PCI cycle. When the PCI
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bus performs burst accesses, the APTA register is
updated by the S5935 to reflect the address of the cur-
rent data phase.
For PCI writes to the Add-On, the S5935 transfers the
data from the PCI bus into the Pass-Thru Data Regis-
ter (APTD). The S5935 captures the data from the PCI
bus when TRDY# is asserted. The PCI bus then
becomes available for other transfers. When the Pass-
Thru data register becomes full, the S5935 asserts the
Pass-Thru status signals to indicate to the Add-On that
data is present. The Add-On logic may read the data
register and assert PTRDY# to indicate the current
access is complete. Until the current access com-
pletes, the S5935 responds to further Pass-Thru
accesses with retries.
For PCI reads from the Add-On, the S5935 asserts the
Pass-Thru status signals to indicate to the Add-On that
data is required. The Add-On logic should write to the
Pass-Thru Data Register and assert PTRDY# to com-
plete the access. The S5935 does not assert TRDY#
to the PCI bus until PTRDY# is asserted by Add-On
logic. If the Add-On cannot provide data quickly
enough, the S5935 signals a retry to the PCI bus. This
allows the PCI bus to perform other tasks, rather than
waiting for a slow target.
Revision 1.02 – June 27, 2006
AMCC Confidential and Proprietary
Data Book