Delphi text file writing log (txt) - WriteLog

procedure WriteLog(Msg : string);
var
  f: TextFile;
  ASBName, FileName : String;
begin
  FileName := FormatDateTime('yyyymmdd', Now);
  ASBName  := GetModuleName(HInstance);
  FileName := ExtractFilePath(ASBName)+FileName;
  //ASBName  := ExtractFileName(ASBName);
  FileName := FileName +'_Log.txt';
  Try
    if not DirectoryExists(ExtractFilePath(FileName)) then
       ForceDirectories(ExtractFilePath(FileName));
    AssignFile(f, FileName);
    if FileExists(FileName) then Append(f) else ReWrite(f);
    if Msg = '' then
      Msg := #13+'System DateTime: '+FormatDateTime('dd/mm/yyyy hh:mm:ss:zzz AM/PM', Now);
    Writeln(f, Msg);
    CloseFile(f);
  Except

  End;
end;