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9. COMMUNICATIONS IN THE NO-PROTOCOL MODE
MELSEC-A
PC CPU
AJ71 C24
Sequence
,
- -
program
I
\
-
1
(1): Setting received data length
(2): Received data read request
I
I
Data
Data
Data
Data
Data
Data
Data
(Received data)
1
2
3
(Completed code)
( n + l )
- -
(n+2)
-
u
1
(279 bytes)
(b) By receiving the set data length (fixed length)
The AJ71C24 makes a request to read the received data to the
sequence program when it has received the set length of data from
an external device.
Using this method, it is possible to receive fixed length data
Default setting is 127 words, but this value may be changed as
required. (For the procedure to change the data length setting, see
Section 7.4.2.)
PC CPU
AJ71 C24
Buffer memory (no-protocol data receive area)
(Received data)
,
Data 1
-
Data 2
program
-
i
,
Da!a
3
I
I
1
-
- D a t a
n - l
L -
-
-
Data n
(Completed data
1
Data ( n i l )
(1): Setting received data length
Data (n+2)
(2): Received data read request
I
1
(279 bytes)
length)
4
(1) When both the receive completed code and the receive completed
data length are set to the special application area in buffer memory,
both of them are effective.
In this case, the one which is met first triggers the read request signal
(Xnl) to the sequence program. See Section 7.4.1 and 7.4.2.
(2) The data received after the reception of the receive completed code
or the set length of data has been received is stored in the OS area
(279 bytes) of the AJ71C24.
The data stored in the OS area is
transferred to the data receive area after the data previously stored
in this area has been read by the sequence program.
In data communications through the RS-232C interface, the DTR signal
is turned OFF to request disconnection of data transmission from the
external device if the available area in the OS area where the receive
data is stored becomes less than 10 bytes. See appendices
4.
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