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IEC 61131-3: Exception Handling with TRY/CATCH

When executing a program, there is always the possibility of an unexpected runtime error occurring. These occur when a program tries to perform an illegal operation. This kind of scenario can be triggered by events such as division by 0 or a pointer which tries to reference an invalid memory address. We can significantly improve the way these exceptions are handled by using the ...

29.07.2019 | 67 2 | Stefan Henneken

IEC 61131-3: Parameter transfer via FB_init

... and can be used to perform initialization tasks. The dialog for adding methods offers a finished template for this purpose. The method contains two input variables that ... is also executed implicitly before the PLC task is started. Both FB_init() methods of FB_SerialCommunication and of FB_SerialCommunicationRS232 are always called implicitly. When inherited, FB_init() is ...

26.07.2019 | 55 0 | Stefan Henneken

IEC 61131-3: The ‘Decorator’ Pattern

... (I_Pizza) defines all common properties and methods . Since the price has to be determined for ... This is helpful, for example, with methods , since each pizza variant can be passed via ... can be additional properties, but also further methods . The function block for the tomatoes is to ... contain an instance of Stream. Many methods and properties of FileStream and MemoryStream access this ...

16.02.2019 | 147 1 | Stefan Henneken

IEC 61131-3: The ‘State’ Pattern

... State transitions in methods The ‘state’ pattern ... State transitions in methods The problem can ... are implemented as methods . If a ... executed in the methods and the state ... shifted to methods , this is ... methods CustomerTakesCoin(), CustomerTakesProduct(), InsertCoin() ... methods have to be ... methods , the individual ... methods (SetState() and SetProducts()) ... methods and properties that ...

17.11.2018 | 184 0 | Stefan Henneken

IEC 61131-3: The generic data type T_Arg

... a separate function for each data type, the same requirements can be implemented much more elegantly with only one function using data type ANY. Some time ago, I had a similar task. A method s hould be developed that accepts any number of parameters. Both the data type and the number of parameters were random. During my first attempt to find solution, I tried to use a variable-length ...

04.07.2018 | 267 0 | Stefan Henneken

IEC 61131-3: The ‘Observer’ Pattern

... a list of observers. Using the methods Attach() and Detach(), the individual Observers ... observer list in an array. The methods for logging on and off the ... subject. The management code for the methods Attach() and Detach() could be moved ... LREAL; fbSubjectBase : FB_SubjectBase; END_VAR The methods Attach() and Detach() can then access ... of observers), the push method s hould be used.

27.05.2018 | 289 1 | Stefan Henneken

IEC 61131-3: Unit-Tests

... library that provides methods for verifying variables (assert methods ). If a ... window. The assert methods are contained in ... of the assert methods always begin with ... for validity. Some methods contain additional parameters. ... have corresponding assert methods . Some special ... using the assert methods . The execution ... cases that test methods of FB_Foo are ... methods validate the overall ...

24.01.2018 | 421 0 | Stefan Henneken

IEC 61131-3: Extend UNION via inheritance

In the post IEC 61131-3: Additional language extensions, I briefly described the UNION. A reader comment has pointed out to me the possibility, that a UNION can also be expanded by EXTENDS. Since this simplifies the handling of a UNION and the norm does not indicate that, I would like to introduce this possibility in a (very) short post. As already described in a post, a UNION makes it ...

24.09.2017 | 369 0 | Stefan Henneken

IEC 61131-3: Parameter transfer via parameter list

Parameter lists are an interesting alternative for transferring parameters to PLC libraries. Strictly speaking, these are global constants (VAR_GLOBAL CONSTANT) whose initialization values can be edited in the Library Manager. When declaring arrays, their boundaries must be defined as constants. At the time of compilation, it must be known how large the array should be. ...

10.09.2017 | 363 2 | Stefan Henneken

IEC 61131-3: Additional language extensions

The focus of my post has been the object-oriented extensions so far. But there are several general, usually not so far-reaching innovations within TwinCAT 3. Below, they are briefly described. Array initialization If a declared array has to be initialized, the list with the initialization values should be set into square brackets. VAR aTest1 : ARRAY [1..5] OF INT : [1, 2, 3, 4, 5]; ...

17.06.2017 | 573 1 | Stefan Henneken

IEC 61131-3: Methods, Properties and Inheritance

... to PLC programming. Methods Previously, a function ... define additional sub-functions (methods ) within a ... by the user. Methods are comparable to ... Just like functions, methods can also contain local variables. Using methods , the above ... Start() and Stop() methods can access internal ... modified by other methods within the function ... Methods can also include ... and methods with no return ...

23.04.2017 | 1033 0 | Stefan Henneken

IEC 61131-3 – The ‘Command’ Pattern

... necessary sequence of methods calls has to ... FB knows, which methods have to be ... buttons using the method S etCommand(). Thus, FB_SwitchPanel ... of the corresponding methods or inputs. Application ... buttons with the method S etCommand(). The method ... designed generically. The method S etCommand() provides possibility ... required methods of the receiver. ... method S etCommand() of the ...

07.12.2016 | 729 0 | Stefan Henneken

IEC 61131-3: Namespaces

The third edition of IEC 61131-3 introduces the concept of namespaces. Namespaces group elements such as variables, function blocks, data types and libraries into coherent units. This means that elements are no longer identified solely using their names, but additionally using the associated namespace. I first started looking at this issue in late 2010 in CoDeSys V3. The ...

22.11.2016 | 740 0 | Stefan Henneken

IEC 61131-3: Arrays with variable length

... and lower array bounds can be queried in the function. Currently, arrays with a variable length can be passed only to VAR_IN_OUT variables of functions, function blocks and methods . (One would hope that VAR_INPUT and VAR_OUTPUT variables will be supported in the future.) Here is an adjusted example: FUNCTION F_CalcSum1DimArray : LREAL VAR_IN_OUT arrData : ARRAY[*] OF LREAL; ...