
5.0 X-Bus Extension
(Continued)
Revision 1.2
103
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Figure 24. Standard Latched Address Mode - X-Bus Write Access Cycle
Turbo Read Transactions.
A Turbo read 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 address 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 placed on data signals XD7-0. The
XSTB0, asserted one 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 stops driving the data bus. At this point, all addresses are available either
at the address outputs of the PC8741x (XA11-0) or in the three latches. The system may require only part of these address-
es, 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 read 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
XRDY
XSTB2
XSTB1
[11-4]
A
XSTB0
Transaction Continues as for Non-Latched Address Mode 0 and Mode 1 Write
for mode 0
Starting point
for mode 1
Starting point
[7-0]
D