Mitsubishi Electric MELSEC Q Series User Manual page 208

(5) Receive processing of response message
A receive processing example on the connected device side is shown below.
Receive the remaining
response messages.
The received data size
is insufficient.
For the Ethernet communication, the TCP socket function is used on a personal computer.
When this function is sent from the send side by calling once, the receive side needs to call the recv function once, or more
than once. (The ratio of the send function and the recv function is not 1 to 1.)
Therefore, the receive processing described above is required for the program processing on the connected device.
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Communication process on the connected device
Request message/send process
Response message/receive process
Is the TCP connection open?
Were the data
received within the monitoring
timer value?
Check the received data size.
Response message process
Have all the received messages
been processed?
End
The TCP connection is closed.
Timeout of the monitoring timer value
If the response message to
the next request has been
received
Error process