write function block with generic data type

Hi all,

Is it possible to write a function block, and for some of the variables use a placeholder instead of specifying the data type, and specify the actual type only at instanciation?

A simple example would be a generic multiplexer:

FUNCTION_BLOCK "FB_generic_mux"

VAR_INPUT

    selector_i : Bool;

    input_0_i  : <TYPE_PLACEHOLDER>;

    input_1_i  : <TYPE_PLACEHOLDER>;

END_VAR

VAR_OUTPUT

    output_o   : <TYPE_PLACEHOLDER>;

END_VAR

BEGIN

    IF #selector_i

    THEN

        #output_o := #input_1_i;

    ELSE

        #output_o := #input_0_i;

    END_IF;

END_FUNCTION_BLOCK

This generic multiplexer could be instanciated several times on variables with different types: 

FUNCTION_BLOCK "FB_custom"

VAR_INPUT

    selector_i          : Bool;

    UDInt_input_0_i     : UDInt;

    Time_input_0_i      : Time;

    String_input_0_i    : String;

    UDInt_input_1_i     : UDInt;

    Time_input_1_i      : Time;

    String_input_1_i    : String;

END_VAR

VAR_OUTPUT

    UDInt_output_o      : UDInt;

    Time_output_o       : Time;

    String_output_o     : String;

END_VAR

VAR

    DB_UDInt_mux        : "FB_generic_mux";

    DB_Time_mux         : "FB_generic_mux";

    DB_String_mux       : "FB_generic_mux";

END_VAR

BEGIN

    #DB_UDInt_mux(

        selector_i := #selector_i,

        input_0_i  := #UDInt_input_0_i,

        input_1_i  := #UDInt_input_1_i,

        output_o   => #UDInt_output_o

    );

    #DB_Time_mux(

        selector_i := #selector_i,

        input_0_i  := #Time_input_0_i,

        input_1_i  := #Time_input_1_i,

        output_o   => #Time_output_o

    );

    #DB_String_mux(

        selector_i := #selector_i,

        input_0_i  := #String_input_0_i,

        input_1_i  := #String_input_1_i,

        output_o   => #String_output_o

    );

END_FUNCTION_BLOCK

Is there any way to achieve this using TIA Portal and SCL language?

Thanks,

- Julien

No.

You can mimic this behavior to some extent by using Variant.

jacek d

No.

You can mimic this behavior to some extent by using Variant.

What he said.. but with one example.

Thanks a lot, I am finally starting to understand variants thanks to your example!

You made my day :)

- Julien 

qwazee

 

jacek d

No.

You can mimic this behavior to some extent by using Variant.

What he said.. but with one example.

When I call the function block, do I map the variables normally, or do I need to make something like AddressOf(variable)?

qwazee

 

jacek d

No.

You can mimic this behavior to some extent by using Variant.

What he said.. but with one example.

julien.reinauld

When I call the function block, do I map the variables normally, or do I need to make something like AddressOf(variable)?

You can link the tag in a normal way.
The variant will handle (almost) any tag.

The compiler does work well enough to tell you if your coding of VARIANT is not right.
There is no substitute in putting the code to the FC / FB.

Some situations are a problem with Step V15 and lower,
where the compiler gives the green light but PLCSIM gives bad results.
I have not found any problems with Step7 / PLCSIM V15.1.

Helpful? More thoughts from you?

Yes, very helpful, many thanks!

I am using v16 or v16.1, so I think it's OK.

I came up with thos toy example (a multiplexer) , can you spot anything wrong?

Thanks again for your help.

qwazee

You can link the tag in a normal way.
The variant will handle (almost) any tag.

The compiler does work well enough to tell you if your coding of VARIANT is not right.
There is no substitute in putting the code to the FC / FB.

Some situations are a problem with Step V15 and lower,
where the compiler gives the green light but PLCSIM gives bad results.
I have not found any problems with Step7 / PLCSIM V15.1.

Helpful? More thoughts from you?

Why are you doing a multiplexer? You can do your task directly.

IF (switch = TRUE) THEN
 OUT := IN1;
ELSE
 OUT := IN2;
END_IF;

The above code is instead of the muliplexer call that you would make. IN1, IN2, OUT and switch are the tags that would have connected on the outside of the FB that you are showing. What I mean is that you do not need to create an extra code block.. direct assignment is possible.

Future reference
To share the code with the forum: Right click on the block and export the text. The copied text can be saved into a text (TXT) file. Add the text file as an attachment.

UPDATE
I find no problem with your idea.. in relation to the code you showed. I have made mine in an FC, see the attached. Also note the software is Step7 V15.1. 

A caution --- All three tags that connect to the VARIANT inputs/output should be of the same type. You cannot hope to push a tag with REAL into a tag that is a DWORD.

Best to mention to us what type of problem crosses your path.

Hi,

Thanks for your help.

Agreed, this is 'useless', it is just a pretext to play with variants.

Once again I would like to thank you for the details and the clarity of your answers, it is very helpful!

- Julien

Do a forum search for 'variant'. You will see some examples that may be worth remembering for the day you need them. Be on the lookout for LGF (Library of General Functions) which are supplied by Siemens and makes good use of VARIANT.

julien.reinauld

Hi,

Thanks for your help.

Agreed, this is 'useless', it is just a pretext to play with variants.

Once again I would like to thank you for the details and the clarity of your answers, it is very helpful!

- Julien

Thank you for the compliment.
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