
XRT7245
DS3 UNI FOR ATM
á
PRELIMINARY
REV. 1.03
52
latched address value will be driven onto
the bi-directional data bus.
Note:
In order to insure that the XRT7245 DS3 UNI device
will interpret this signal as being a “Read” signal, the μC/μP
should keep the WRB_RW input pin “High”.
B.2
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
asserting the Rdy_Dtck (DTACK*) signal.
B.3
After the μC/μP detects the Rdy_Dtck signal
(from the SRT7245 DS3 UNI), it terminates the
“Read” cycle by toggling the RdB_DS (Data
Strobe) input pin “high”.
For subsequent read operations, within this burst cycle,
the μC/μP simply repeats steps B.1 through B.3, as
illustrated in Figure 17.
3.2.2.2.2.1.3
Terminating the Burst Access
Operation
The Burst I/O Access will be terminated upon the fall-
ing 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 exe-
cute either a “Programmed I/O” access or to start an-
other “Burst Access”O(jiān)peration with the XRT7245
DS3 UNI.
3.2.2.2.2.2
The “Motorola-Mode” Write Burst
Access
Whenever a “Motorola-type” μC/μP wishes to write
the contents of numerous registers or buffer locations
over a “contiguous” range of addresses, then it
should do the following.
Perform the initial “write” operation; of the
burst access.
Perform the remaining “write” operations,
of the burst access.
Terminate the burst access operation.
a.
b.
c.
Each of these “operations” within the burst access
are described below.
3.2.2.2.2.2.1
The initial write operation of a “Motorola-type” Write
Burst Access is accomplished by executing a “Pro-
grammed I/O Write Cycle” as summarized below.
Execute a Single Ordinary (Programmed I/O)
Write cycle, as described in Steps A.1
through A.7 below.
The Initial Write Operation
A.
A.1
Assert the ALE_AS (Address Strobe) input pin
by toggling it “l(fā)ow”. This step enables the
Address Bus input drivers (within the XRT7245
DS3 UNI).
A.2
Place the address of the “initial”target register
or buffer location (within the UNI), on the
Address Bus input pins, A[8:0].
A.3
At the same time, 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 μC/
μP and the UNI Microprocessor Interface block.
A.4
After allowing the data on the Address Bus pins
to settle (by waiting the appropriate “Address
Setup” time), the μC/μP should toggle the
ALE_AS input pin “high”. This step causes the
UNI device to “l(fā)atch” the contents of the
F
IGURE
17. B
EHAVIOR
THE
M
ICROPROCESSOR
I
NTERFACE
S
IGNALS
,
DURING
SUBSEQUENT
“R
EAD
” O
PERATIONS
WITHIN
THE
B
URST
I/O C
YCLE
(M
OTOROLA
-
TYPE
μC/μP)
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)