Programming interface 
  4.2 Error and status messages 
SIMATIC 3964R protocol for Windows 9x/XP/7 
Installation Manual, 01/2013, J31069-D0131-U001-A2-7218 
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4.2  Error and status messages 
Messages returned by the functions described in the previous section can be divided into 
three classes:  
●  Positive status messages 
●  Status error messages 
●  System error messages 
The following error codes are defined in the header file "3964r.h". 
Positive status messages 
 
Used by: 
•  ComReadState 
•  ComWriteState 
The status messages are returned when: 
●  an operation was completed successfully 
●  an event was not evaluated as an error 
 
Status messages 
COM_ST_FREE  Everything OK, no job present 
COM_ST_BUSY  A job is currently being processed, no error has occurred up to now. 
COM_ST_SUCCESS  The last operation was completed successfully.