Interfaces Blogs & News @CODEKICKER

4

IEC 61131-3: Different versions of the same library in a TwinCAT project

Library placeholders allow to reference multiple versions of the same library in a PLC project. This situation can be helpful if a library has to be updated in an existing project due to new functions, but the update turns out to give an older FB a changed behavior. The mentioned problem can be solved by including different versions of the same library in the project using ...

02.04.2021 | 51 2 | Stefan Henneken

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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 | 483 3 | Stefan Henneken

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IEC 61131-3: Parameter transfer via FB_init

Depending on the task, it may be necessary for function blocks to require parameters that are only used once for initialization tasks. One possible way to pass them elegantly is to use the FB_init() method. Before TwinCAT 3, initialisation parameters were very often transferred via input variables. (* TwinCAT 2 *) FUNCTION_BLOCK FB_SerialCommunication VAR_INPUT nDatabits : ...

26.07.2019 | 415 0 | Stefan Henneken

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IEC 61131-3: The ‘Decorator’ Pattern

... properties of FileStream and MemoryStream access this instance. You can also say: The subclasses FileStream and MemoryStream decorate Stream. Further use cases are libraries for the creation of graphical user interfaces . These include WPF from Microsoft as well as Swing for Java. A text box and a border are nested into each other; the text box is decorated with the border. The ...

16.02.2019 | 676 3 | Stefan Henneken

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IEC 61131-3: The ‘State’ Pattern

... The same applies to elements that are declared as PRIVATE. FBs, interfaces , methods and properties that are only used within a library, can ... the object has changed its class.” Implementation A common interface (S tate) is defined, which contains a method for each state ... each state, a class is created that implements this interface (S tate1, State2, …). As all states have the same ...

17.11.2018 | 527 0 | Stefan Henneken

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IEC 61131-3: The generic data type T_Arg

In the article The wonders of ANY, Jakob Sagatowski shows how the data type ANY can be effectively used. In the example described, a function compares two variables to determine whether the data type, data length and content are exactly the same. Instead of implementing a separate function for each data type, the same requirements can be implemented much more elegantly with only ...

04.07.2018 | 599 0 | Stefan Henneken

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IEC 61131-3: The ‘Observer’ Pattern

... change. Never program directly to implementations, but always to interfaces . The assignment between input and output variables must ... This can be realized elegantly with the help of interfaces that define the communication between the FBs. There is ... (FB_Base)? Multiple inheritance is not possible (however, several interfaces can be implemented). Here, it makes sense to embed ...

27.05.2018 | 626 3 | Stefan Henneken

10

IEC 61131-3: Unit-Tests

Unit tests are an essential tool for every programmer to ensure functioning of his software. Software bugs cost time and money, so you need an automated solution to find these bugs and preferably before the software is used. Unit tests should be used wherever software is professionally developed. This article is intended to provide a quick introduction and allow an ...

24.01.2018 | 844 2 | Stefan Henneken

9

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 | 688 0 | Stefan Henneken

7

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 | 689 2 | Stefan Henneken

3

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 | 987 1 | Stefan Henneken

4

IEC 61131-3: Methods, Properties and Inheritance

... Polymorphism always occurs in the context of inheritance and interfaces . We will illustrate polymorphism using the above example with inheritance. We ... function block can then be passed to this function. Interfaces are also important in this context and this is explored in my post IEC 61131-3: Object composition using interfaces . SUPER pointer In the above example, we created a ...

23.04.2017 | 1621 0 | Stefan Henneken

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IEC 61131-3: Methoden, Eigenschaften und Vererbung (Update)

... abgeleitet wurden, können somit an die Funktion übergeben werden. In diesem Zusammenhang spielt auch das Konzept der Schnittstellen (Interfaces ) eine wichtige Rolle, welches in meinem Post IEC 61131-3: Objektkomposition mit Hilfe von Interfaces vorgestellt wird. SUPER-Zeiger Bei dem obigen Beispiel wurde in FB_NewEngine die Methode Start() neu angelegt und der schon ...

04.04.2017 | 1771 0 | Stefan Henneken

11

IEC 61131-3 – The ‘Command’ Pattern

... of the 8-button keypad. Thus, a scene controller could be implemented, with which the user can himself allocate the commands to a scene over an interactive user interface. S ample 2 (TwinCAT 3.1.4020) Undo functionality A further possible feature is a cancellation function. The 8-button keypad gets a further input which undoes the last executed command. For this purpose, the ...

07.12.2016 | 1019 0 | Stefan Henneken

6

IEC 61131-3: Namespaces

... elements from libraries. The namespace should also be entered when defining function blocks derived from function blocks from a library and when using interfaces from a library: FUNCTION_BLOCK FB_MyFoo EXTENDS MyNamespace01.FB_Foo IMPLEMENTS MyNamespace01.I_Foo VAR_INPUT END_VAR VAR_OUTPUT END_VAR VAR END_VAR The dialog for creating new FBs supports this process: ...

22.11.2016 | 1086 0 | Stefan Henneken

11

IEC 61131-3: Namensräume

... der Namespace benutzt werden. Auch bei der Definition von FBs die von einem FBs aus einer Bibliothek erben, als auch bei der Verwendung von Interfaces aus Bibliotheken sollte der Namespace angegeben werden: FUNCTION_BLOCK FB_MyFoo EXTENDS MyNamespace01.FB_Foo IMPLEMENTS MyNamespace01.I_Foo VAR_INPUT END_VAR VAR_OUTPUT END_VAR VAR END_VAR Der Dialog zum Anlegen von ...

15.11.2016 | 1261 0 | Stefan Henneken

10

IEC 61131-3: Arrays with variable length

While declaring arrays, one had always to define a constant value up to now. Since the 3rd edition of the IEC 61131-3, arrays can be declared with a variable length. Thus, you can create functions much more generically than previously. Although, variables can be used for array bounds, they have to be declared as constants. An adaption of the array bounds is thus not possible at ...

27.09.2016 | 1192 0 | Stefan Henneken

7

IEC 61131-3: Das ‘Command’ Pattern

Durch den Aufruf einer Methode kann an einem Funktionsblock ein Befehl ausgeführt werden. Funktionsblock A ruft eine Methode von Funktionsblock B auf. So weit so gut. Doch wie lässt sich der Austausch solcher “Befehle” zwischen mehreren Funktionsblöcken flexibel gestalten? Das Command Pattern liefert hier einen interessanten Ansatz. Ein kleines Beispiel aus der ...

14.08.2016 | 1112 0 | Stefan Henneken

7

IEC 61131-3: The Pattern ‘Abstract Factory’

... bodies stay void. In this way, an abstract function block can be compared with an interface. S ince the class factory is derived from an abstract class (here: abstract function block), it is ... factory. The new language features of IEC 61131-3 have made it possible. Interfaces , inheritance and dynamic memory management offer entirely new approaches in design of PLC libraries.

16.11.2014 | 1605 0 | Stefan Henneken

8

IEC 61131-3: Das Pattern ‘Abstract Factory’

... Open Closed Principle. Fazit Durch den Einsatz einer abstract Factory konnte der Baustein FB_Logger in seiner Funktionalität erweitert werden, ohne dass dieser geändert wurde. Die neuen Sprachfeatures der IEC 61131-3 haben dieses möglich gemacht. Interfaces , Vererbung und die dynamische Speicherverwaltung bieten völlig neue Ansätze im Design von SPS-Bibliotheken.

05.09.2014 | 2297 0 | Stefan Henneken

5

IEC 61131-3: Object composition with the help of interfaces

... readily and frequently, interfaces are rather rarely applied. However, interfaces provide a number of benefits, which ... the possibilities of interfaces relating to the IEC 61131-3 standard. ... as a benchmark. Interfaces Interfaces deal with definition of methods and ... a “is-a” relationship, interfaces can be described as ... methods of the interfaces without concrete knowledge of ...

18.02.2014 | 1221 1 | Stefan Henneken

5

IEC 61131-3: Object composition with the help of interfaces

... readily and frequently, interfaces are rather rarely applied. However, interfaces provide a number of benefits, which ... the possibilities of interfaces relating to the IEC 61131-3 standard. ... as a benchmark. Interfaces Interfaces deal with definition of methods and ... a “is-a” relationship, interfaces can be described as ... methods of the interfaces without concrete knowledge of ...

18.02.2014 | 1190 1 | Stefan Henneken

9

IEC 61131-3: Objektkomposition mit Hilfe von Interfaces

... der Einsatz von Interfaces eher selten behandelt. Dabei bieten Interfaces etliche Vorteile, die die Flexibilität eines ... die Möglichkeiten von Interfaces in Zusammenhang mit der IEC ... als Richtwert dienen. Interfaces Bei Interfaces handelt es sich um ... darstellen, könnte man Interfaces als eine ‘verhält-sich-wie-ein-Beziehung’ ... die Methoden des Interfaces auf, ohne konkret ...

30.01.2014 | 1269 1 | Stefan Henneken

11

IEC 61131-3: Objektkomposition mit Hilfe von Interfaces

... der Einsatz von Interfaces eher selten behandelt. Dabei bieten Interfaces etliche Vorteile, die die Flexibilität eines ... die Möglichkeiten von Interfaces in Zusammenhang mit der IEC ... als Richtwert dienen. Interfaces Bei Interfaces handelt es sich um ... darstellen, könnte man Interfaces als eine ‘verhält-sich-wie-ein-Beziehung’ ... die Methoden des Interfaces auf, ohne konkret ...

30.01.2014 | 3040 1 | Stefan Henneken

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