Revision 1.02 – June 27, 2006
S5935 – PCI Product
Data Book
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).
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.
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.
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.
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
150
DS1527
AMCC Confidential and Proprietary
AMCC [ APPLIED MICRO CIRCUITS CORPORATION ]
