Siemens SIMATIC S7 System Manual page 528

Libraries
9.4 Open user communication library
Network 7: Call the TCP_CONNECT instruction with Req = FALSE and the same
Connection ID (ConnID) as above. Do this to check the connection status and ensure that
the CPU established the connection.
Network 8: If Done is TRUE, this means that the CPU established the connection, so
continue in the "Idle" state.
If Busy is TRUE, stay in the "Connect Wait" state. The TCP_CONNECT instruction
eventually times out and returns an error if the other device is not present, so you do not
need to have a time out mechanism for the connect process.
If Error is TRUE, there is a problem connecting to the passive device. In this case, just try
again by going back to the "Connect" state. Note that if the passive device is present but it
rejects the connection request, the connection errors very quickly and utilizes a great amount
of bandwidth as the CPU continues to attempt to create a connection.
In all cases, exit the state machine for this scan. The program continues to the next state on
the next scan.
Network 9: State "Idle"...
This state puts a time delay between messages so that you do not flood the network. The
symbol "IdleTimeDelay" specifies the delay time.
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System Manual, V2.3, 07/2017, A5E03822230-AF
S7-200 SMART