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