Inheritance Blogs & News @CODEKICKER

6

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

7

IEC 61131-3: Parameter transfer via FB_init

... nStopbits : 2), (nDatabits : 7, eParity : E_Parity.Even, nStopbits : 2)]; Inheritance If inheritance is used, the method FB_init() is always inherited. FB_SerialCommunicationRS232 is used here as an example: ... implemented for two reasons: If FB_SerialCommunication is located in a library, the inheritance cannot be changed just offhand. The call sequence of FB_init() is not ...

26.07.2019 | 55 0 | Stefan Henneken

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IEC 61131-3: The ‘Decorator’ Pattern

... the principle of inheritance . In the following post, I ... The ‚Hell of Inheritance ‘ In the second approach, a ... results in an inheritance hierarchy that reflects the dependencies of ... desired. The entire inheritance hierarchy must be adapted. The solution ... firm relationship through inheritance . How does the system handle ... not rely on inheritance when behaviour is extended. Rather, ...

16.02.2019 | 147 1 | Stefan Henneken

9

IEC 61131-3: The ‘State’ Pattern

State machines are used regularly, especially in automation technology. The state pattern provides an object-oriented approach that offers important advantages especially for larger state machines. Most developers have already implemented state machines in IEC 61131-3: one consciously, the other one perhaps unconsciously. The following is a simple example of three ...

17.11.2018 | 184 0 | Stefan Henneken

7

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 | 267 0 | Stefan Henneken

7

IEC 61131-3: The ‘Observer’ Pattern

... subject (FB_SubjectNew), it can be inherited from this base class (FB_SubjectBase). But what if this special function block (FB_SubjectNew) already inherits from another base class (FB_Base)? Multiple inheritance is not possible (however, several interfaces can be implemented). Here, it makes sense to embed the base class in the new function block, i.e. to create a local ...

27.05.2018 | 289 1 | 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 | 421 0 | Stefan Henneken

9

IEC 61131-3: Extend UNION via inheritance

... nA, nB : BYTE; END_VAR uVar.nVar1 : 16#1234; nA : uVar.stVar2.nLSB; // Value: 16#34 (LSB) nB : uVar.stVar2.nMSB; // Value: 16#12 (MSB) EXTENDS for UNIONS The same task can also be solved with inheritance , which is a bit more elegant. In this case, the union U_Test inherits from ST_Bytes. TYPE U_Test EXTENDS ST_Bytes : UNION nVar1 : WORD; // stVar2 : ST_Bytes; // Not necessary, is ...

24.09.2017 | 369 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 | 363 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 | 573 1 | Stefan Henneken

4

IEC 61131-3: Methods, Properties and Inheritance

... has the following structure: PROPERTY : Inheritance Function blocks are an excellent means ... the concept of inheritance . Inheritance is one of the fundamental principles of object-oriented programming. Inheritance involves deriving a new function block ... from outside FB_NewEngine. Inheritance applies only to POUs of type ... be used for inheritance . No restrictions ...

23.04.2017 | 1033 0 | Stefan Henneken

11

IEC 61131-3 – The ‘Command’ Pattern

A command can be run on a function block by calling a method. Function block A calls a method of function block B. So far, so good, but how can such “commands” be exchanged flexibly between several function blocks. The command pattern provides an interesting approach. A small example from the home automation should help us at this. Suppose we have several FBs which represent each a ...

07.12.2016 | 729 0 | Stefan Henneken

6

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

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 | 803 0 | Stefan Henneken

7

IEC 61131-3: The Pattern ‘Abstract Factory’

... by implementing this Open Closed Principle. Conclusion The functionality of the block FB_Logger could be extended without modifying the block itself through the application of an abstract 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 | 1283 0 | Stefan Henneken

8

IEC 61131-3: Das Pattern ‘Abstract Factory’

Sollen Instanzen eines Funktionsblocks anlegt werden, so muss vor dem Compilieren der genaue Typ des Funktionsblocks bekannt sein. Durch diese feste Zuordnung kann das Verhalten einer Anwendung nur schwer erweitert werden. Dieses ist z.B. der Fall, wenn sich der Funktionsblock in einer Bibliothek befindet und somit der Zugriff auf den Quellcode nicht möglich ist. Die ...

05.09.2014 | 1942 0 | Stefan Henneken

5

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

... the notion of inheritance is used readily and frequently, interfaces ... the IEC 61131-3 standard. Inheritance appears to be the best known ... in the following. Inheritance If one deals with the concept ... would notice that inheritance is its best known feature. It ... to the subclasses, inheritance of properties and methods can be ... i.e. possibilities of inheritance can also be constrained ...

18.02.2014 | 944 1 | Stefan Henneken

5

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

... the notion of inheritance is used readily and frequently, interfaces ... the IEC 61131-3 standard. Inheritance appears to be the best known ... in the following. Inheritance If one deals with the concept ... would notice that inheritance is its best known feature. It ... to the subclasses, inheritance of properties and methods can be ... i.e. possibilities of inheritance can also be constrained ...

18.02.2014 | 964 1 | Stefan Henneken

9

Diamanten in Java

Java verfügt weder über Mehrfach- noch über Mixin-Vererbung. Insofern erscheint eine Diskussion des Diamant-Problems reichlich müßig. Trotzdem bin ich gerade darüber gestolpert, und habe einen Ansatz entwickelt, der – allerdings auf Kosten der Übersichtlichkeit – Code-Duplizierung vermeidet. Nehmen wir an, folgende Interfaces seien gegeben: public interface Base { ...

25.01.2012 | 1042 0 | eSCALAtion Blog

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