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Can I connect function block input or output with variable? Like IEC61131-3 [message #1791284]

Wed, 27 June 2018 15:08

Henry Bao

Messages: 8
Registered: June 2018

Junior Member

Hello, does 4DIAC IDE support local or global variable like IEC61131-3, for example, I can use variable in F_ADD IN1/IN2/OUT, use variable is much flexible, IEC61131-3 support it, but I can not find in 4DIAC IDE, or I may have mistake to use 4DIAC IDE ?

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Re: Can I connect function block input or output with variable? Like IEC61131-3 [message #1791290 is a reply to message #1791284]

Wed, 27 June 2018 16:22

Alois Zoitl

Messages: 636
Registered: January 2014

Senior Member

IEC 61499 does not have global variables. Therefore 4diac also does not support them. You can have local variables inside of FBs, which are called internal vars in IEC 61499.

Cheers,
Alois

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Re: Can I connect function block input or output with variable? Like IEC61131-3 [message #1791955 is a reply to message #1791290]

Mon, 09 July 2018 03:18

Henry Bao

Messages: 8
Registered: June 2018

Junior Member

Hi Alois,

From the programming point of view, it is better have global veriables to connect to FBs, not only connect FBs to constant value or connect between FBs.

If I want to extend it, could you give me some suggestion for that?

Best Regards,
Henry

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Re: Can I connect function block input or output with variable? Like IEC61131-3 [message #1791971 is a reply to message #1791955]

Mon, 09 July 2018 08:45

Martin Melik-Merkumians

Messages: 45
Registered: March 2016

Member

Hi Henry,

I disagree strongly that global variables are either needed, or improve something from the programming point of view. If you REALLY NEED to get a similar effect, you can also use PUBLISH/PUBL and SUBSCRIBE/SUBL, although I would recommend to restructure your program to eliminate the need for a global variable!

Best regards,
Martin

[Updated on: Mon, 09 July 2018 08:45]

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Re: Can I connect function block input or output with variable? Like IEC61131-3 [message #1791975 is a reply to message #1791971]

Mon, 09 July 2018 09:30

Alois Zoitl

Messages: 636
Registered: January 2014

Senior Member

Hi,

I agree here with Martin and would add a strong warning towards the PUBL/SUBL approach as in my experience I noticed that these leads to very hard to understand and maintain programs.

There is a very good reason that IEC 61499 does not provide global variables: in distributed systems global variables are very hard to implement and to use correctly.

As I pointed out above maybe Basic Function Blocks with their internal vars and with the algorithm local vars (i.e., BEGIN_VAR i:INT; END_VAR) are the solution you are looking for.

Cheers,
Alois

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Re: Can I connect function block input or output with variable? Like IEC61131-3 [message #1792003 is a reply to message #1791975]

Mon, 09 July 2018 16:03

Henry Bao

Messages: 8
Registered: June 2018

Junior Member

Hi Alois, I start to understand your suggestion by using Basic Function Blocks, I will change the concept of application programming. IEC61499 is really different concept than pure IEC61131-3 programming, even IEC61499 extend lots of feature from IEC61131-3.

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