PROGRAM PLC_PRG
VAR
   first: BOOL:= TRUE;   
   application: POINTER TO APPLICATION;
   result: POINTER TO RTS_IEC_RESULT;
   storeRetains: BOOL := FALSE;
END_VAR
//NOTE: Flash memory has a high but limited amount of write cycles before it will begin to wear out.  This means that the user should be careful not to write to flash
//too often to avoid wear.  It is recommeneded to only write persistent variables when changes are made to the persistent variable and not in a cyclic manner.
//This function is executed at startup only once to load what is in the function.
IF(first) THEN
   //Get the current application for use by the restore retains function below
   application:=AppGetCurrent(pResult:=result);
   
   //This function restores the retained variables from the file 'Application.ret' into the current application.  
   //If you keep the file name of your persistant variable file 'Application.ret' this function should not be needed as CODESYS should automatically retore
   //the retain file at startup.  This is just shown as an example in case the user would like to maintain different retain files
   AppRestoreRetainsFromFile(pApp:=application, pszFilname:='Application.ret');
   first:= FALSE;
END_IF
//this function will execute one time when the 'storeRetains' boolean variable is turned to true;
IF(storeRetains) THEN
   //this is a test retain variable.  It will start at 0 since it is initialized that way in the PersistentVars object.
   //Everytime this function is executed the persistent variable will increase by 1 and store its new value
   test_persist_var:= test_persist_var + 1;
   //Get the current application for use by the restore retains function below
   application:=AppGetCurrent(pResult:=result);
   //Store the variables listed in the 'PersistentVars' object into the file 'Application.ret'.
   //You may change the file name to anything you prefer but the 'Application.ret' should be loaded automatically by CODESYS so if the file name is changed you
   //may need to load the file yourself as shown above
   AppStoreRetainsInFile(pApp:=application, pszFilname:='Application.ret');
   
   //CODESYS and the Linux filesystem keep files open for approximately 40 seconds after the write to reduce wear on the flash memory.  If power is abruptly lost
   //during that period of time the retains file can be corrupted and all user data can be lost.  Issuing the 'sync' command below to the Linux filesystem
   //will force the file to write and sync with the filesystem making it very difficult for the file to be corrupted.
   ShellCommand_System(command:='sync');
   
   //turn the 'storeRetains' variable back to false so this fuction won't execute until it is turned back to true
   storeRetains:= FALSE;
END_IF

   sFileName      :   File.CAA.FILENAME   :=   'Application.ret';
   hFileHandle   :    File.CAA.HANDLE;
   FileFlush      :   File.Flush();

   FileFlush ( xExecute:= storeRetains );