
á
PRELIMINARY
DS3 UNI FOR ATM
XRT7245
REV. 1.03
47
A.2
While the μC/μP is placing this address value
onto the Address Bus, the Address Decoding
circuitry (within the user’s system) should assert
the CS* input pin of the UNI, by toggling it
“l(fā)ow”. This step enables further communication
between the μP/μC and the UNI Microproces-
sor Interface block.
A.3
Assert the ALE_AS (Address Latch Enable)
pin by toggling it “high”. This step enables the
“Address Bus” input drivers, within the Micro-
processor Interface block of the UNI.
A.4
After allowing the data on the Address Bus
pins to settle (by waiting the appropriate
“Address” Data Setup time”), the μC/μP should
then toggle the ALE_AS pin “l(fā)ow”. This step
latches the contents, on the Address Bus pins,
A[8:0], into the XRT7245 DS3 UNI Micropro-
cessor Interface block. At this point, the “initial”
address of the burst access has now been
selected.
Note:
The ALE_AS input pin should remain “l(fā)ow” for the
remainder of this “Burst Access” operation.
A.5
Next, the μC/μP should indicate that this current
bus cycle is a “Read” Operation by toggling the
RdB_DS (Read Strobe) input pin “l(fā)ow”. This
action also enables the “bi-directional” data bus
output drivers of the UNI device. At this point,
the bi-directional data bus output drivers will
proceed to drive the contents of the
“addressed” register onto the “bi-directional”
data bus, D[15:0].
A.6
Immediately after the μC/μP toggles the “Read
Strobe” signal “l(fā)ow”, the UNI device will toggle
the Rdy_Dtck (READY) output pin “l(fā)ow”. The
UNI device does this in order to inform the μC/
μP that the data (to be read from the data bus)
is “NOT READY” to be latched inot the μC/μP
A.7
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”.
A.8
After the μC/μP detects the Rdy_Dtck signal
(from the XRT7245 DS3 UNI IC), it can then
will terminate the “Read” cycle by toggling the
RdB_DS (Read Strobe) input pin “high”.
Figure 12 presents an illustration of the behavior of
the Microprocessor Interface Signals, during the “ini-
tial” Read Operation, within a Burst I/O Cycle; for an
Intel-type μC/μP
At the completion of this initial read cycle, the μC/μP
has read in the contents of the first register or buffer
location (within the XRT7245 DS3 UNI) for this partic-
ular burst I/O access operation. In order to illustrate
how this “burst access operation” works, the byte (or
word) of data, that is being read in Figure 12 has
been labeled “Valid Data at Offset = 0x00”. This label
indicates that the μC/μP is reading the very first register
(or buffer location) in this burst access operation.
The Subsequent Read Operations
The procedure that the μC/μP must use to perform
the remaining read cycles, within this Burst Access
operation, is presented below.
3.2.2.2.1.1.2
F
IGURE
12. B
EHAVIOR
OF
THE
M
ICROPROCESSOR
I
NTERFACE
S
IGNALS
,
DURING
THE
“I
NITIAL
” R
EAD
O
PERATION
OF A
B
URST
C
YCLE
(I
NTEL
T
YPE
P
ROCESSOR
).
ALE_AS
RDB_DS
A[8:0]
CS*
D[15:0]
Rdy_Dtck
Not Valid
Valid Data of Offset = 0x00
Address of “Initial” Target Register (Offset = 0x00)
WRB_RW