
á
PRELIMINARY
DS3 UNI FOR ATM
XRT7245
REV. 1.03
49
3.2.2.2.1.2
The “Intel-Mode” Write Burst
Access
Whenever an “Intel-type” μC/μP wishes to write data
into 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.
3.2.2.2.1.2.1
The Initial Write Operation
The initial write operation of an “Intel-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.
A.
A.1
Place the address of the “initial” target register
(or buffer location) within the UNI, on the
Address Bus pins, A[8:0].
A.2
At the same time, the “Address-Decoding” cir-
cuitry (within the user’s system) should assert
the CS* (Chip Select) input pin of the UNI, by
toggling it “l(fā)ow”. This step enables further com-
munication between the μC/μP and the UNI
Microprocessor Interface block.
A.3
Assert the ALE_AS (Address Latch Enable)
input pin “high”. This step enables the Address
Bus input drivers, within the Microprocessor
Interface Block of the UNI.
A.4
After allowing the data on the Address Bus
pins to settle (by waiting the appropriate
“Address Setup” time); the μC/μP should then
toggle the ALE_AS input 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 I/O Access” operation.
A.5
Next, the μC/μP should indicate that this cur-
rent bus cycle is a “Write” operation by keeping
the RdB_DS pin “high” and toggling the
WRB_RW (Write Strobe) pin “l(fā)ow”. This action
also enables the “bi-directional” data bus input
drivers of the UNI device.
A.6
The μC/μP places the byte (or word) that it
intends to write into the “target” register on the
“bidirectional data” bus, D[15:0].
A.7
After waiting the appropriate amount of time,
for the data (on the bi-directional data bus) to
settle, the μC/μP should toggle the WRB_RW
(Write Strobe) input pin “high”. This action
accomplishes two things.
a.
It latches the contents of the bi-directional
data bus into the XRT7245 DS3 UNI
Microprocessor Interface Block.
It terminates the write cycle.
b.
Figure 14 presents a timing diagram which illustrates
the behavior of the Microprocessor Interface signals,
during the “initial” write operation within a Burst
Access, for an “Intel-type” μC/μP
F
IGURE
14. B
EHAVIOR
OF
THE
M
ICROPROCESSOR
I
NTERFACE
SIGNALS
,
DURING
THE
“I
NITIAL
” W
RITE
O
PERATION
OF A
B
URST
C
YCLE
(I
NTEL
-
TYPE
P
ROCESSOR
)
ALE_AS
A[8:0]
CS*
D[15:0]
Not Valid
Valid Data at Offset =0x01
RDB_DS
Not Valid
Valid Data at Offset =0x02
WRB_RW
Address of “Initial” Target Register (Offset = 0x00)