TwinCAT 3 : Block stays busy - plc

Question

I want to save some data into a .txt file. I can create it, but I can't write text into it because the FB stays busy.
CASE counter OF
1:
fileOpen.sNetId := '';
fileOpen.sPathName := 'C:\test\test.txt';
fileOpen.nMode := FOPEN_MODEWRITE;
fileOpen.bExecute := TRUE;
fileOpen.tTimeout := T#200MS;
fileOpen();
counter := 2;
2:
IF NOT fileOpen.bBusy AND NOT fileOpen.bError THEN (* bBusy stays true*)
counter := 3;
END_IF
3:
fileOpen.bExecute := FALSE;
fbPutFile(sNetId := '', hFile := fileOpen.hFile, sLine := 'FOO', bExecute := TRUE, tTimeout := INT_TO_TIME(200), bBusy =>, bError =>, nErrId =>);
END_CASE
I get into step 2, but I can't get into step 3. Where is the problem?

Answer 1

It's because you have stopped calling the function block for opening the file. What you're doing here is that you're calling the FB_FileOpen in step 1, but then stop calling it. The bBusy-flag goes high (true) in step1, but can never be changed to anything else as you never call the FB again. You need to make a call to it in step2 as well. Remember that bExecute is also a trigger for the ADS-command, so once you've done it in step 2, you can set the bExecute-input to FALSE in step2 and forward as you've already triggered the command.
...
2:
fileOpen(bExecute := false);
IF NOT fileOpen.bBusy AND NOT fileOpen.bError THEN (* bBusy stays true*)
counter := 3;
END_IF
...
Also remember that Beckhoffs FB_FileOpen assumes that the directory C:\test exists (though not the file test.txt if you open it with FOPEN_MODEWRITE it will be automatically created). To create all necessary directores (if they don't already exist) use TwinCATs FB_CreateDir.