Checking The Receive Data Length; Precautions For Active Open - Mitsubishi Electric MELSEC iQ-RJ71EN71 User Manual

■Checking the receive data length

There is no concept of delimiting the communication data during communication with TCP/IP. Thus, the continuously sent
data may be merged on the received side, or the data sent in a group may be split on the receive side. If necessary, the
receiving side must check the receive data length and perform the processing.
If the data length is determined when receiving with the Ethernet-equipped module side, using the fixed-length mode is
recommended.
When receiving on the external device side, check the receive data length and perform the processing as shown below.
Receive the rest of the message.

■Precautions for Active open

Use 'Open completion signal' (Un\G1900000 to Un\G1900007) and 'Open request signal' (Un\G1900008 to Un\G1900015) in
the program to create an interlock circuit. The on/off timing for the open completion signal and open request signal is shown
below.
'Open completion signal'
(Un\G1900000 to Un\G1900007)
'Open request signal'
(Un\G1900008 to Un\G1900015)
1 FUNCTIONS
64
1.4 Socket Communications
Receive processing on the external device side
Received message, receive processing
Is TCP connection open?
Received data within
the time specified by the monitoring
Check the received data size.
NO
Sufficient receive data size?
Processing for the received message
Was the entire received message
<When disconnected by the Ethernet-equipped module>
ON
OFF
ON
OFF
OPEN instruction
<When disconnected by the external device>
⋅⋅⋅
⋅⋅⋅
YES
timer value?
YES
YES
processed?
YES
End
TCP disconnection completed upon response from the external device
TCP disconnection request from the Ethernet-equipped module
CLOSE instruction
TCP disconnection request from the external device
TCP disconnection completed upon response from the Ethernet-equipped module
CLOSE instruction
NO
TCP connection is closed.
NO
NO
Error handling