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9. COMMUNICATIONS IN THE NO-PROTOCOL MODE
MELSEC-A
A1 SCPU
A1 SJ71 C24
Buffer memory (no-protocol data receive area)
(Received data)
-
Data 1
Sequence
+--
-
Data 2
program
i
-
Data 3
i
i
-
-Data
n-1
-
-
Data n
(Completed code)
-Data
(n+l)
-
(1): Sening received data length
Data (n+2)
-
(2): Received data read request
I
I
(304 bytes)
(b) By receiving the set data length (fixed length)
TheAlSJ71 C24 makes a request to read the received datato thesequence
Droaram when it has received the set lenrrth of datafrom 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.)
A1 SCPU
A1 SJ7t C24
Buffer memory (no-protocol data receive area)
1
Received data)
-
Data 1
(
-
Data 2
-
DaJa 3
-
-
~ a t a n-1
7
-
Data n
cL
Data (n+l)
(Completed data
(1): Setting received data length
(2): Received data read request
length)
POINTS
(
(1) When both the receive completed code
and
the receive completed data length
areset to tkspecialapplicationareain buffer memory, both ofthernareeffect've.
In this case, theonewhich 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 (304
bytes) of the AlSJ71C24. The datastored 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.
When the size of the vacant area in the OS area, where received data is
stored, becomes smaller than 10 bytes, the following control operations
are executed according to preset transmission control specifications.
When the DTR control has been set: the A1 SJ71 C24 turns OFF the DTR
signal and makes a request to terminate the send from the communicat-
ing equipment (see Appendix 5).
When the DCI-DC3 code transmission control has been set: the
A1 SJ71 C24 sends a DC3 code and makes a request to terminate the send
from the communicating equipment (see Appendix 5.1).
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