Revision 1.02 – April 12, 2007
S5920 – PCI Product: Operation Registers
Data Book
The following describes one of the four configuration registers. All four region configuration registers are exactly
the same.
Table 48. Pass-thru Configuration Register
Bit
Description
7
PTADR# mode. This bit is only valid in Active mode. If this bit is 0, PTADR# is not driven at the beginning of a
Active cycle. If this bit is set to 1 (default state), the S5920 will assert PTADR# for one clock cycle after PTATN#
is asserted. The Pass-Thru address is also driven while PTADR# is low. This bit is a don’t care if the device is
operating in Passive mode
6
5
Endian conversion. If this bit is set to one, the S5920 will convert the Add-On bus from the default little endian
format to a big endian format.
Write FIFO disabled. If this bit is set to 1, the S5920 will not accept the next piece of data (on a PCI write) until
the Add-On has accepted the previous piece of data. If this bit is set to 0, the S5920 will accept data from the
PCI until the Pass-Thru write FIFO is full.
4:3
2:0
Prefetch. These bits control the number of DWORDs that the S5920 will prefetch after the current PCI Pass-
Thru read completes. The actual amount of data prefetched depends upon any number of different scenarios.
The prefetch values of “small,” “medium” and “large” are available to tune the system to achieve best overall
performance (i.e. optimize PCI bus transfers or optimize Add-On bus transfers). The Pass-Thru read FIFO can
be enabled to prefetch in either Active mode or Passive mode.
Wait states. In Active mode, the user can program the number of wait states required by the Add-On bus to
complete a transaction. Up to 7 wait states can be programmed (per region). The S5920 will count the number
of clocks programmed into this register before finishing the current data transaction if PTRDY# is high. If
PTRDY# is driven low, additional wait states may be inserted. Bits 2, 1 and 0 are don’t care if operating in Pas-
sive mode.
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