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MODBUS TCP Master/Slave Communication
Timing chart
Clear to send master
communication flag
(X90 - X9F)
Sending master
communication flag
(Y90 - Y9F)
Execute SEND
Master communication
Sending done result flag
(Y70 - Y7F)
Sending data
Response reception
processing
I/O Allocation
I/O number
Clear to send master
X90 - X9F
communication flag
Sending master
Y90 - Y9F
communication flag
Y70 - Y7F
Sending done result flag
(Note 1) Each contact is used for reading the operation status. Do not write over it with a user program.
KEY POINTS
•
Specify the connection No. targeted for communication, using UNITSEL
command immediately before SEND/RECV command.
•
Master communication is only valid when MEWTOCOL or MODBUS is
selected. Confirm that the "clear to send master communication flag" (X90 -
X9F) for the targeted connection is ON, and execute SEND/RECV command.
•
You cannot execute other SEND/RECV command for connection in master
communication. Confirm that the "sending master communication flag"
(Y90 - Y9F) is OFF, and execute command.
•
You cannot execute SEND/RECV command for connection in slave
communication.
Up to 16 SEND/RECV commands can be executed simultaneously for
•
different connections.
•
In the MODBUS-TCP mode, specify the partner station no. for the operand
of SEND/RECV command.
6-10
Confirm ON
Confirm OFF
Name
When connection is ON in the master communication mode, the
flag is ON.
Turns ON during sending data based on SEND/RECV command.
Turns OFF when ED command is executed following response
reception processing.
Reports completion result of sending data in general-purpose
communication or master communication.
(Normal completion: 0, Abnormal completion: 1)
Conditions to enable execution of SEND
command
Clear to send flag (X90 - X9F): ON
Sending flag (Y90 - Y9F): OFF
Sending flag (Y90 - Y9F):
During the sending process: ON
During execution of ED command
following response reception processing:
OFF
Sending done result flag (Y70 - Y7F):
Normal completion: OFF
Abnormal completion: ON
Explanation
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