
á
DS3/E3 FRAMER IC
XRT7250
REV. 1.1.1
49
a. The Framer internally increments the latched
address value (within the Microprocessor Inter-
face circuitry).
b. The output drivers of the bi-directional data bus
(D[7:0]) are enabled. At some time later, the reg-
ister or buffer location corresponding to the incre-
mented latched address value will be driven onto
the bi-directional data bus.
NOTE: In order to insure that the XRT7250 DS3/E3 Framer
device will interpret this signal as being a Read signal, the
C/P should keep the WR_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 C/P. The XRT7250 DS3/E3
Framer will indicate that this data is ready to be
read by asserting the RDY_DTCK (DTACK*)
signal.
B.3
After the C/P detects the RDY_DTCK signal
(from the XRT7250 DS3/E3 Framer), it termi-
nates the Read cycle by toggling the RD_DS
(Data Strobe) input pin "High".
For subsequent read operations, within this burst cy-
cle, the C/P simply repeats steps B.1 through B.3,
2.2.2.2.2.1.3
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
Framer will cease to internally increment the latched
address value. Further, the C/P is now free to exe-
cute either a Programmed I/O access or to start an-
other Burst Access Operation with the XRT7250 DS3/
E3 Framer.
2.2.2.2.2.2
The Motorola-Mode Write Burst
Access
Whenever a Motorola-type C/P wishes to write the
contents of numerous registers or buffer locations
over a contiguous range of addresses, then it should
do the following.
a. Perform the initial write operation of the burst
access.
b. Perform the remaining write operations, of the
burst access.
c. Terminate the burst access operation.
Each of these operations within the burst access are
described below.
2.2.2.2.2.2.1
The Initial Write Operation
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.
A.0
Execute a Single Ordinary (Programmed I/
O) Write cycle, as described in Steps A.1
through A.7 below.
A.1
Assert the ALE_AS (Address Strobe) input pin
by toggling it "Low". This step enables the
Address Bus input drivers (within the XRT7250
DS3/E3 Framer).
A.2
Place the address of the initial target register or
buffer location (within the Framer), on the
Address Bus input pins, A[8:0].
A.3
At the same time, the Address-Decoding cir-
cuitry (within the user's system) should assert
the CS input pin of the Framer by toggling it
"Low". This step enables further communica-
FIGURE 34. BEHAVIOR THE MICROPROCESSOR INTERFACE SIGNALS, DURING SUBSEQUENT READ OPERATIONS
WITHIN THE
BURST I/O CYCLE (MOTOROLA-TYPE C/P)
ALE_AS
RD_DS
A[8:0]
CS
D[15:0]
RDY_DTCK
Not Valid
Valid Data at Offset
WR_RW
Not Valid
Valid Data at Offset
Address of “Initial” Target Register (Offset =