S7 Input pointer inside multi instance

Why does my deconstruction of the input pointer only work with its own instance DB not inside the multi instance FB...See .doc The pointer at the input is P#i258.0


Any help appreciated.

adamplc said:

Why does my deconstruction of the input pointer only work with its own instance DB not inside the multi instance FB...See .doc The pointer at the input is P#i258.0


Any help appreciated.

Click to expand...

The images are not clear enough to decipher them and, I personally can barely understand STL in English so posting it in what appears to be Arabic language is not helpful.
I suggest you describe the problem you are having.
I understand that you are calling a FB with a pointer as actual parameter to one of its inputs.
The problem you are having is that when you instantiate the FB as a single instance you get different result from when you instantiate it as mutliple instance .

My answer is, there should not be any difference. There has to be something else changing the value you are seeing.

The problem I have is the area part of the pointer is not pointing to an input location when using it inside a multi instance block call. When using it with its own instance the area pointer is correct.


single instance

16#81000810 = 1000 0001 0000 0000 0000 1000 0001 0000

area crossing pointer of type input


multi instance

16#4010001 = 0000 0100 0000 0001 0000 0000 0000 0001
area crossing pointer of global DB



I don't know why the area pointer is not working inside a multi instance FB and works outside in a single instance.

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I think that it is because you are using temp data for storing. Change temps to stat-area for test.



Are you sure that your animation show temp data for this FB or something later values as temps are writed over on plc scan.

When I open that doc on my phone it shows some crazy characters but on the laptop it is english.


How did you create your instance FBs?



Have a look at this and see if is helpful.
"Note:
When you create multiple instances, please bear in mind that the FB, which is called as a multiple instance, is always created first and then assigned a multiple instance call. If you do not follow this procedure, there might be inconsistencies in the program. These inconsistencies also occur if you make changes to a multiple instance."

When you access an interface variable (except a temp variable) in an FB, the code in the background combines AR2 as the base address and adds the offset for the variable to give the final address to access the variable. This is the basis for multi-instance - AR2 is setup to point to the base address of the interface data for the instance, and then in the instance you refer to the offset. With a single instance AR2 will be set to zero, hence your code works, with a multi instance you need to add AR2 to access the same variable.

Example showing how to access multi-instance parameters indirectly.

Perfect exactly what I needed…you are a master of the Siemens world!
Much appreciated.

BTW, in your code snippet you are accessing local data by address (LB 0 etc.) - generally to be avoided as the editor will sometimes use this area and you can get unexpected results.