Mitsubishi MELSEC L Series User Manual page 50

(d) Precaution for Passive open communication
• Configure an interlock circuit using the Open completion signal (SD1282) and Open request signal
(SD1284) in the program.
The following chart shows on/off timings of the Open completion signal and Open request signal.
Open completion signal
(SD1282)
Open request signal
(SD1284)
• When a device establishes a connection by Passive open, the IP address and port number of the
connected device can be acquired using the SP.SOCCINF instruction.
For the SP.SOCCINF instruction, refer to:
• On TCP, one connection is established with one target device.
To communicate with multiple devices from one port number, prepare the same number of connections as
that of the target devices.
A connection that exceeds the preset number of connections will be disconnected immediately.
• Do not accept a connection from a device until the CPU module is placed in the wait-for-open state.
If a TCP connection request is received before entering the wait-for-open state after completion of CPU
startup, the request will be recognized as an error, and a forced close message for the connection will be
returned to the interfacing device.
In this case, wait until the CPU state is changed to the wait-for-open state and then retry the connection
from the device.
• Do not execute the SP.SOCCLOSE instruction in a 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 a closed connection, execute the SP.SOCOPEN instruction.
For the SP.SOCOPEN instruction, refer to:
48
ON
OFF
ON
OFF
TCP connection completed
by the external device
TCP disconnection completed
by the external device
Page 75, Section 6.4.6
Page 58, Section 6.4.1
Always on