Siemens SIMATIC S7 System Manual page 542

Libraries
9.4 Open user communication library
Network 19: If Done is TRUE, the send is complete so go to the "Receive" state.
If Busy is TRUE, stay in the "Transmit Wait" state.
If Error is TRUE, check the reason for the error and change the state if there is a connection
issue.
Network 20: State "Disconnect"...
Initiate a disconnect.
Network 21: Initiate the disconnect with the ConnID by calling the DISCONNECT instruction
with Req = TRUE.
Network 22: If Done is TRUE, this means that the disconnect is complete (probably will
never happen), so try to reconnect.
If Busy is TRUE (this would be normal), go to the "Disconnect Wait" state.
If Error is TRUE, check the reason, and you may need to change state if there is a
connection issue.
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System Manual, V2.3, 07/2017, A5E03822230-AF
S7-200 SMART