
XRT7245
DS3 UNI FOR ATM
á
PRELIMINARY
REV. 1.03
46
3.2.2.2
Burst Mode I/O access is a much faster way to transfer
data between the μC/μP and the Microprocessor Inter-
face (of the XRT7245 DS3 UNI), than Programmed I/O.
The reason why Burst Mode I/O is so much faster
follows.
Data is placed upon the Address Bus input pins
A[8:0]; only for the very first access, within a given
burst access. The remaining read or write operations
(within this burst access) do not require the place-
ment of the Address Data on the Address Data Bus.
As a consequence, the user does not have to wait
through the “Address Setup” and “Hold” times; for
each of these Read/Write operation, within the
“Burst” Access.
It is important to note that there are some limitations
associated with Burst Mode I/O Operations.
All cycles within the Burst Access, must be either
“all Read” or “all Write” cycles. No “mixing of
“Read” and “Write” cycles is permitted.
A Burst Access can only be used when “Read” or
“Write” operations are to be employed over a
contiquous range of address locations, within the
UNI device.
The very first “Read” or “Write” cycle, within a
burst access, must start at the “l(fā)owest” address
value, of the range of addresses to be accessed.
Subsequent operations will automatically be incre-
mented to the very next higher address value.
Data Access Using Burst Mode I/O
1.
2.
3.
Examples of Burst Mode I/O operations are presented
below for read and write operations, with both “Intel-
type” and “Motorola-type” μC/μP
3.2.2.2.1
If the XRT7245 DS3 UNI is interfaced to an “Intel-
type” μC/μP (e.g., the 80x86 family, etc.), then it
should be configured to operate in the “Intel” mode
(by tying the “MOTO” pin to ground). Intel-type
“Read” and “Write” Burst I/O Access operations are
described below.
Burst I/O Access in the Intel Mode
3.2.2.2.1.1
Whenever an “Intel-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 of
the burst access.
Terminate the “burst access” operation.
The “Intel-Mode” Read Burst Access
a.
b.
c.
Each of these “operations” within the burst access
are described below.
3.2.2.2.1.1.1
The Initial Read Operation
The initial read operation of an “Intel-type” read burst
access is accomplished by executing a “Programmed
I/O” Read Cycle as summarized below.
Execute a Single Ordinary (Programmed I/O)
Read 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 input pins A[8:0].
F
IGURE
11. I
LLUSTRATION
OF
THE
B
EHAVIOR
OF
THE
M
ICROPROCESSOR
I
NTERFACE
SIGNAL
,
DURING
A
“M
OTOROLA
-
TYPE
” P
ROGRAMMED
I/O W
RITE
O
PERATION
.
ALE_AS
A[8:0]
CS*
D[15:0]
RDB_DS
Rdy_Dtck
Data to be Written
Address of Target Register
WRB_RW