■Use of UDP
Data may be lost, or may arrive out of order. Consider using TCP if any problem is expected.
■Sending and receiving data
Data sending process may complete normally even if the communication line between the CPU module and target device is
not connected due to a reason such as cable disconnection. To avoid this, it is recommended to provide communication
procedure at the user's discretion.
■Open completion signal and Open request signal
Once UDP is selected for a connection, the Open completion signal and Open request signal of the connection are always on.
Do not execute the SP.SOCCLOSE instruction in the program.
Doing so will disable data transfer since the Open completion signal and Open request signal of the corresponding connection
turn off for close processing.
To reopen the closed connection, execute the SP.SOCOPEN instruction.
For the SP.SOCOPEN instruction, refer to Page 84 Opening a connection.
This section provides other precautions for the socket communication function.
Host station port number, 1 to 1023 (0001H to 03FFH), are assigned for reserved port numbers (WELL KNOWN PORT
NUMBERS) and 61440 to 65534 (F000H to FFFEH) are for other communication functions. Therefore, using 1024 to 5548,
5570 to 61439 (0400H to 15ACH, 15C2H to EFFFH) is recommended.
Do not specify 5549 to 5569 (15ADH to 15C1H) because these ports are used by the system.
Do not specify 45237 (B0B5H) and 61440 to 65534 (F000H to FFFEH) for the socket communication function when using the
iQ Sensor Solution-compatible function.
When using the following functions, do not specify the port number reserved for the socket communication function.
• File Transfer Function (FTP server): 20 (14H), 21 (15H)
• Web server function: 80 (50H)
• Time setting function (SNTP client): 123 (7BH)
• SLMP function: 61440 (F000H), 61441 (F001H)
• CC-Link IE field network Basic: 61450 (F00AH)
*1 Port No. can be changed. (Default: 80)
Reading received data
Read received data when the Receive state signal (SD10682.n) has turned on.
Communication via the built-in Ethernet port may be affected if a considerable amount of received data has not been read for
a long time.
Conditions for closing
In TCP communication, even if no close request is sent from the connected device, the Open completion signal will turn off to
close the connection in the following cases.
• Alive check is timed out.
• Forced close is received from the connected device.
7 SOCKET COMMUNICATION FUNCTION