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FIXED BUFFER COMMUNICATION (WITH THE PROCEDURE EXIST
CONTROL METHOD)
6
6 - 1
6
MELSEC-F
6 FIXED BUFFER COMMUNICATION (WITH THE PROCEDURE EXIST
CONTROL METHOD)
This chapter explains how the PLC and external device communicate in a 1:1 mode
using the fixed buffers (with the procedure exist control method) of the Ethernet
module.
6.1 Control Method
The following explains how communication is performed using the fixed buffers and
the procedure exist control method.
In communication using the fixed buffers, data transmission from the PLC and the
external device is executed through handshaking.
(1) The data flow during communication is as follows.
(2) Data can be communicated with the following external devices.
• Device on the Ethernet to which the Ethernet module is connected.
• Devices connected with the router relay function (see Section 5.3)
As shown in the diagram below, when using each fixed buffer (No. 1 to 8), the
destination devices and usage conditions (for sending/receiving, procedure exist/
no procedure, etc.) should be set when the connection via the Ethernet module is
opened to fix the external device for each buffer.
(a) At TCP/IP communication
It is allowed to change external devices only when the open completion
signal of the applicable connection is off.
(b) At UDP/IP communication
External devices can be changed regardless of the status of the applicable
connection.
("Destination IP address" and "Destination Port No." in the communication
address setting area can be changed. However, the "Local station Port No."
cannot be changed.)
When changing external devices, do not use the "Pairing open" and
"Existence confirmation" functions.
FX3U
main
unit
Fixed buffer
No.1
No.2
No.3
No.4
No.8
External device
TO instruction (Transmission request)
FROM instruction (Reading the data received)
FROM instruction (Transmission complete)
TO instruction (Reception complete)
(For sending)
(For receiving)
For sending to external device 1
Fixed buffer No. 1
External device 1
External device 8
For receiving from external
device 1
Fixed buffer No. 2
For receiving from external
device 8
Fixed buffer No. 3
For sending to external
device 28
Fixed buffer No. 8
For receiving from
external device 28