
XRT7245
DS3 UNI FOR ATM
á
PRELIMINARY
REV. 1.03
48
B.
Execute each subsequent Read Cycles, as
described in Steps B.1 through B.3 below.
B.1
Without toggling the ALE_AS input pin (e.g.,
keeping it “l(fā)ow”); toggle the RdB_DS input pin
“l(fā)ow”. This step accomplishes the following.
a.
The UNI will internally increments the
“l(fā)atched address” value (within the Micro-
processor Interface circuitry).
The output drivers of the “bi-directional”
data bus, D[15:0] are enabled. At some
time later, the register or buffer location
corresponding to the “incremented”
latched address value will be driven onto
the bidirectional data bus.
b.
B.2
Immediately after the “Read Strobe” pin toggles
“l(fā)ow” the UNI IC will toggle the Rdy_Dtck
(READY) output pin “l(fā)ow” to indicate its “NOT
READY” status.
B.3
After some settling time, the data on the bi-
directional data bus will stabilize and can be
read by the μC/μP The XRT7245 DS3 UNI will
indicate that this data is ready to be read by
toggling the Rdy_Dtck (READY) signal “high”.
B.4
After the μC/μP detects the Rdy_Dtck signal
(from the XRT7245 DS3 UNI), it can then ter-
minates the “Read” cycle by toggling the
RdB_DS (Read Strobe) input pin “high”.
For subsequent read operations, within this burst cycle,
the μP/μC simply repeats steps B.1 through B.3, as
illustrated in Figure 13.
In addition to the behavior of the Microprocessor In-
terface signals, Figure 13 also illustrates other points
regarding the “Burst Access Operation”.
The UNI internally increments the address
value, from the original “l(fā)atched” value in
Figure 13. This is illustrated by the data,
appearing on the data bus, (for the first read
access) being labeled “Valid Data at Offset =
0x01”; and that for the second read access
being labeled “Valid Data at Offset = 0x02.”.
a.
b.
The UNI performs this “address increment-
ing” process even though there are no
changes in the Address Bus Data, A[8:0].
Terminating the Burst Access
Operation
The Burst Access Operation will be terminated upon
the rising edge of the ALE_AS input signal. At this
point the UNI will cease to internally increment the
“l(fā)atched” address value. Further, the μC/μP is now
free to execute either a “Programmed I/O” access or
to start another “Burst Access” Operation with the
XRT7245 DS3 UNI.
3.2.2.2.1.1.3
F
IGURE
13. B
EHAVIOR
OF
THE
M
ICROPROCESSOR
I
NTERFACE
S
IGNALS
,
DURING
SUBSEQUENT
“R
EAD
” O
PERATIONS
WITHIN
THE
B
URST
I/O C
YCLE
.
ALE_AS
RDB_DS
A[8:0]
CS*
D[15:0]
Rdy_Dtck
Not Valid
Valid Data at Offset =0x01
WRB_RW
Not Valid
Valid Data at Offset =0x02
Address of “Initial” Target Register (Offset = 0x00)