XRT7245
DS3 UNI FOR ATM
á
PRELIMINARY
REV. 1.03
50
At the completion of this initial write cycle, the μC/μP
has written a byte or word into the first register or
buffer location (within the XRT7245 DS3 UNI) for this
particular burst access operation. In order to illustrate
this point, the byte (or word) of data, that is being
written in Figure 14; has been labeled “Data to be
Written (Offset = 0x00)”.
The Subsequent Write Operations
The procedure that the μC/μP must use to perform
the remaining write cycles, within this burst access
operation, is presented below.
Execute each subsequent write cycle, as
described in Steps B.1 through B.3.
3.2.2.2.1.2.2
B.
B.1
Without toggling the ALE_AS input pin (e.g.,
keeping it “l(fā)ow”); apply the value of the next
byte or word (to be written into the UNI) to the
bi-directional data bus pins, D[15:0].
B.2
Toggle the WRB_RW (Write Strobe) input pin
“l(fā)ow”. This step accomplishes two things.
a.
It enables the input drivers of the bi-direc-
tional data bus.
It causes the UNI to internally increment
the value of the “l(fā)atched” address.
After waiting the appropriate amount of settling
time the data, in the internal data bus, will sta-
bilize and is ready to be latched into the UNI
Microprocessor Interface block. At this point,
the μC/μP should latch the data into the UNI by
toggling the WRB_RW input pin “high”.
b.
B.3
For subsequent write operations, within this burst I/O
access, the μC/μP simply repeats steps B.1 through
B.3, as illustrated in Figure 15.
3.2.2.2.1.2.3
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.
Terminating the Burst I/O Access
3.2.2.2.2
Burst I/O Access in the Motorola
Mode
If the XRT7245 DS3 UNI is interfaced to a “Motorola-
type” μC/μP (e.g., the MC680x0 family, etc.), then it
should be configured to operate in the “Motorola” mode
(by tying the “MOTO” pin to VCC). Motorola-type
“Read” and “Write” Burst I/O Access operations are
described below.
3.2.2.2.2.1
The “Motorola-Mode” Read Burst
I/O Access Operation
Whenever a “Motorola-type” μC/μP wishes to read
the contents of numerous registers or buffer locations
over a “contiguous” range of addresses, then it
should do the following.
Perform the initial “Read” operation of the
burst access.
Perform the remaining “read” operations; in
the burst access.
Terminate the “burst access” operation.
a.
b.
c.
F
IGURE
15. B
EHAVIOR
OF
THE
M
ICROPROCESSOR
I
NTERFACE
S
IGNALS
,
DURING
SUBSEQUENT
“W
RITE
”
O
PERATIONS
WITHIN
THE
B
URST
I/O C
YCLE
.
ALE_AS
WRB_RW
A[8:0]
CS*
D[15:0]
Rdy_Dtck
Data Written at Offset =0x01
RDB_DS
Data Written at Offset =0x02
Address of “Initial” Target Register (Offset = 0x00)