
5.0 X-Bus Extension
(Continued)
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Figure 25. Turbo Latched Address Mode - X-Bus Read Access Cycle
Turbo Write Transactions.
A Turbo write cycle starts by outputting the lower 12 address signals on address signals
XA11-0 and by outputting address lines 27-20 on data signals XD7-0 on the rising edge of the clock. One CLK cycle later,
a strobe signal (XSTB2) is asserted to latch the address in an external latch. One CLK cycle after that, a second set of ad-
dress lines (19-12) is placed on data pins XD7-0. These can be latched by the strobe signal XSTB1, asserted one cycle later
on the rising edge of the clock. One CLK cycle later, the last group of address lines (11-4) is output on the data signals XD7-
0. The XSTB0, asserted one CLK cycle later on the rising edge of the clock, can be used to latch this part of the address.
One CLK cycle later on the rising edge of the clock, the PC8741x outputs the data signals on data pins XD7-0. At this point,
all the addresses are available either at the address outputs of the PC8741x (XA11-0) or at the outputs of the three latches.
The system may require only part of these addresses, depending on the size of the memory or peripheral address space.
One CLK cycle later, the chip-select signal XCSn is asserted, based on the XCSn Turbo mode setting. From this point, the
write continues as described for the Normal Address Turbo transaction, Mode 0. XSTB2-0 are de-asserted one CLK cycle
after the de-assertion of XCSn. At this time, the latched address becomes invalid. At the same time, the address signals
XA11-0 are driven to low level.
CLK
(Internal; for
Reference Only)
XD7-0
XA27-0
(After Latching)
XA11-0
(Availability on Device Pins
Depends on Multiplexing)
XCSn
XWR_XRW
[27-20]
A
[19-12]
A
XRD_XEN
XSTB2
XSTB1
XSTB0
Transaction Continues as for Non-Latched, Turbo X-Bus Address Mode 0 Read
[11-4]
A
Starting point