Download MELSEC-L CPU Module User`s Manual (Built-In

7.3
Precautions for the Socket Communication Function
This section provides other precautions for the socket communication function.
(1) Port number
Host station port number, 0001H to 03FFH, are assigned for reserved port numbers (WELL KNOWN PORT
NUMBERS) and F000H to FFFEH are for other communication functions. Therefore, using 0400H to 1387H and
1392H to EFFFH is recommended.
Do not specify 1388H to 1391H because these ports are used by the system. (Page 214, Appendix 2)
Do not specify 0014H and 0015H for the socket communications function when using the file transfer function
(FTP server).
Do not specify 007BH for the socket communication function when using the time setting function (SNTP).
Do not specify F000H to FFFEH for the socket communication function when using the data logging file transfer
function.
Do not specify B0B5H and F000H to FFFEH for the socket communication function when using the iQ Sensor
Solution function.
(2) Reading out received data
Read out received data when the Receive state signal (SD1286) has turned on.
Communication via the built-in Ethernet port may be affected if a considerable amount of received data have not
been read out for a long time.
(3) Conditions for closing
In TCP communications, 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.
(4) Elements for TCP connection
The following four elements control TCP connections, and only one connection can be established with a unique
setting for these elements. To use multiple TCP connections at the same time, at least one of the four elements
must be different.
• IP address of the CPU module
• Port number of the CPU module
• IP address of the target device
• Port number of the target device
(5) Reestablishment of the same connection
Allow eight seconds or more before reestablishing a connection of the same target IP address, the same host
station port number, and the same target port number after closing it.
If the reestablishment is time-critical, it is recommended to change the host station port number on the Active
open side.
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