Mitsubishi Electric MELSEC iQ-R Series User Manual page 254

(0) The refresh processing of the module label is performed. (The processing is required when using the module function block.)
When the refresh processing is completed, 'Refresh execution status' (M0) is turned on.
(44) When M1 is turned on, open processing of connection No.1 is performed. When the open processing is completed successfully, M3 is turned on.
(173) When M5 is turned on, the send data is stored and data is sent to the external device of connection No.1. When the data send is completed successfully,
M7 is turned on.
(243) When M13 is turned on, the close processing of connection No.1 is performed. When the close processing is completed successfully, M15 is turned on.
11 PROGRAMMING
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11.4 Example of Socket Communications