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FIXED BUFFER COMMUNICATION (WITH THE NO PROCEDURE
CONTROL METHOD)
7
7 - 1
7
MELSEC-F
7 FIXED BUFFER COMMUNICATION (WITH THE NO PROCEDURE
CONTROL METHOD)
This chapter explains how the PLC and external device communicate using the fixed
buffers (with the no procedure control method) via the Ethernet module.
7.1 Control Method
The following explains how communication is performed using the fixed buffers and
the no procedure control method.
In communication using the fixed buffers, data transmission from the PLC and the
external device is executed using the no procedure control method.
(1) The data flow during communication is as follows.
POINT
The following points describe the difference from the "Procedure exist" using fixed
buffer communication:
1) It is possible to send and receive data which match the message format of the
external device.
At data sending, subheader, data length, etc. are not included in the
application data field of a message; only the data in the fixed buffer is sent.
Upon data reception, all the data in the message excluding the header is
stored in the fixed buffer.
2) A response to data receiving is not sent.
3) Communication is performed using binary code regardless of the
communication data code settings (see Section 4.6, "Operational Settings").
4) The maximum application data area is 2046 bytes per communication.
5) The applicable connection is dedicated to the no procedure fixed buffer
communication.
As with the procedure fixed buffer communication, and communication using
MC protocol cannot be performed at the same time as the no procedure fixed
buffer communication.
Fixed buffer
No.1
No.2
No.3
No.4
No.8
External
device
FROM instruction
(Reading the received data)
FROM instruction
(Transmission complete)
TO instruction
(Sending request)
TO instruction
(Reception complete)
FX
3U
main
unit
(For sending)
(For receiving)