VAR CONSTANT extended explanation

PLCnext Technology & PLCnext Controls
1

Dear All!
Please let me know, where can i find out some additional info about declaration of constant variables in data type worksheets. ( Constant variables have to be declared as VAR CONSTANT in the data type worksheet using a VAR CONSTANT…END_VAR …)
I need to know it’s visibility scope. Can it be declared in one sheet and used in another. Can this constants be used in POUs, ect. May be some one have examples…
Best regards

2

Hi Oleksandr,
I have discussed this with the PLCnext Engineer support team, and we don’t know where this information came from:
Constant variables have to be declared as VAR CONSTANT in the data type worksheet using a VAR CONSTANT…END_VAR … In PLCnext Engineer, constants can be declared in the Variable worksheet of a POU, or in the global Data List, by ticking the “Constant” checkbox for the variable. The scope of these constants is the same as for other non-constant variables in the same list. There are some restrictions on the use of constants, which are described in the PLCnext Engineer help.

3

Dear Martin,
The information is from the embeded help system of PLCNext 2022.6

                                          * Home -> IEC 61131-3 Programming -> Data Types -> User-defined Data Types ->Arrays

Can be finded out by keywords “VAR CONSTANT” in the SEARCH tab or INDEX tab…
Is there some thing else we can find out about this declaration method?
Best regards

4

Hi Oleksandr,
Fundamentally Var_Constant declaration is the same as selecting “constant” when declaring a local or global variable. - From Home > IEC 61131-3 > Programming > Variables > Variable/Port Properties .
The reason you can declare them on a datatype sheet is so you can declare ARRAY limits using a constant variable (as per IEC61131 spec) as ARRAYS can only be declared on these sheets. These sheets have no “variables” table, so we must declare as VAR CONSTANT text.
The constant variables created using this method are only local to the datatype sheet and cannot be used on another sheet, or as a variable in a POU (in my experience). They are purely for array limit declaration on the sheet.

Best Regards