siemens Step7: REAL or DINT

[obi wan]

Hi,

How can I know if a value is double integer or real? I use this for a check a input parameter in a function.

Thx.

 

[JesperMP]

You cannot be "unsure" of a parameters type.
All input and output parameters must have their type defined when you set them up.

 

[obi wan]

no, I can put a real value if I use MD200 for example

 

[JesperMP]

No, if you try to enter a DINT parameter to a REAL input, or vice-versa, it will not be accepted by the editor.

 

[TurpoUrpo]

If you add that MD200 to symbol table, then you can assing type that step7 can check for it.

 

[TurpoUrpo]

Jesper think this:

call fc1(
in1 := md200
)

how can editor know is md200 real or dint if it is not in symbol table.

 

[JesperMP]

I didnt assume that there was no symbol assigned to MD200.
That is certainly possible, but also very poor programming style.

 

[TurpoUrpo]

Yes. That is why i directed him to add symbol.

 

[JesperMP]

Anyway, it is not possible to check if the incoming values in the parameters are DINTs or REALs.
All possible bit combinations can be represented as a DINT value, and all but a few bit combinations can be represented as a REAL value. How to know that a bit combinmation is a DINT or a REAL ?
One way could be to check for values outside certain limits that cannot be "realistic". But it will be a lot of work, and will not be bulletproof. All just to catch that the idiot programmer dont use symbols.

edit: I dont mean to say that obi wan is an idiot. I assume that obi wan is refering to that someone else may use his FC, and he want to check if it is done right.

 

[obi wan]

This situation can be

Hi,

I want only to say that this situation can be.
I post 2 *.jpg file with a function that convert seconds in hours, minutes, seconds.
We can see 2 different situation with 2 values dint and real from a DB. How can I protect the user of function for this situation? Sure, I can convert real value to dint but it is not correct.

bye

 

[PeterW]

erm....

The Programmer ensures it by only loading in DINT's into the DWORD used.

 

[Jeebs]

Options > Customize > LAD/FBD > Select: Type Check of Addresses

The Editor will not allow a variable declared as REAL to be used on a FC input that is declared as a DInt.

Other than that, there is no way to check/prevent it.

 

[JesperMP]

Whatever I try, I cannot get the editor to accept a variable with a REAL symbol on a DINT input, regardless if type checking is on or not. So I cannot recreate the situation in the screenshot.

Obi wan, how did you get that screenshot ? Did you just change "representation" from "decimal" to "floating point" ? That has nothing to do with the checking of the variables type. That is just how the value is displayed when looking online.

 

[obi wan]

I changed the DB value with right-click/Modify...
Sorry if I dust-up with my question. But I just wanted more information.
Thanks for your support.

 

[JesperMP]

In the S7 program, it cannot happen by accidence, as long as you use symbols.
In a Siemens HMI, it also cannot happen by accidence, if the HMI uses the symbols from the STEP7 project.
If using OPC, it also cannot happen by accidence, if using symbols from the STEP7 project.
If not using symbols, it requires a lot more attention and care of what you do.

Anyway, as I wrote before it is not possible to do a test for REAL or DINT.