Communication Structure - Mitsubishi Electric MELSEC-L SERIES Basic User Manual

12.2

Communication Structure

This section describes the structure of communications using a fixed buffer.
(1) Data flow
In communications using a fixed buffer, data is sent/received using dedicated instructions.
• Sending data: BUFSND instruction
• Receiving data: BUFRCV instruction or BUFRCVS instruction
When the "Procedure Exist" control method is used, the CPU module and the connected device communicate on
a 1:1 basis. The CPU module sends/receives data to/from the connected device while handshaking with the
connected device.
When the "No Procedure" control method is used, the CPU module sends/receives data to/from the connected
device in a non-procedural manner.
CPU module
(2) Connected devices where data communications can be performed
Data communications can be performed with the following connected devices.
• Devices in Ethernet where an E71 is connected
• Devices connected with the router relay function
When using each fixed buffer (numbers 1 to 16) as shown in the figure below, set the destination devices and
usage conditions (e.g. for sending/receiving and "Procedure Exist"/"No Procedure") in the open setting to fix a
connected device to each buffer.
Fixed buffer No.1
Fixed buffer No.2
Fixed buffer No.3
Fixed buffer No.16
Note the following points when changing connected devices.
• During TCP/IP communications, a connected device can be changed only when the connection with the
connected device is not established (when Open completion signal is off).
• During UDP/IP communications, a connected device can be changed regardless of the status of connection
with the connected device.
Fixed buffer
BUFSND instruction
BUFRCV instruction
To send data to the connected device 1
To receive data from the connected device 1
To receive data from the connected device 8
To send data to the connected device 28
CHAPTER 12 COMMUNICATIONS USING A FIXED BUFFER
E71
No.1
No.2
No.3
No.4
Connected device
No.16
Connected device 1
Connected device 8
Connected device 28
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