Warning message on using AR2 in a function block

Hello everyone, 

I have a warning message when using AR2 in TIA Portal, CPU 1512 of the ET200SP module. The warning says "Modification of the register AR2 has no effect on the symbolic instance accesses." (please refer to the picture below).

What does this mean? I have been using AR2 before with ET200S in SIMATIC Manager, and I have never seen any kind of similar warning. Does it have to do something with the CPU I am using? Could someone explain to me what this exactly mean?

I have to emphasize that this warning only appears when I am using AR2 in a FB, but it doesn't appear if I use it in FC block. Why?

How can I turn off this message and is it a safe thing to do? Even with this warning my code works properly. 

Kind regards,

Aleksandra

Hello,

why do you need the AR2 when you program with symbolic operations.

What do you want to do?

The AR2 is at a 1500 not necessary.
Please look at the "Programming Guideline".

Please tell us more about your challenge.

regards
CaOd

CaOd

Hello,

why do you need the AR2 when you program with symbolic operations.

What do you want to do?

The AR2 is at a 1500 not necessary.
Please look at the "Programming Guideline".

Please tell us more about your challenge.

regards
CaOd

 Hello CaOd,

I need AR2 for indirect addressing, and I use it for indirect addressing (more precisely for transferring data between some global DB and instance DB). 

Easier and more elegant solution is to set AR1 address value to point to source DB, and set AR2 value to point to the destination DB, and then just write L and T instructions like this:

L DBD [ AR1 , P#0.0 ]

T DID [ AR2 , P#16.0 ]

I have done the same thing hundred times so far, in Simatic Manager with ET200s.

If I don't use AR2, I would have to first transfer data from source DB to some temp variables via AR1, then update the AR1 value to point to the destination DB, and then tranfer data via AR1 from temp variables to destination DB variables.

I have tried to google this warning, and I found no posts from other users about this.

Hello,

that is right at Step7 classic and a S7-300/400.

If you want to move data between a DB and a instance DB it's at the S7-1500 easier with

• optimized DB
• MOVE instruction
• variant input an output 

Then it's easier to program it for a 1500 system.
There are more possibilities to move data as the S7-300, it's also very different between TIA and Step7 classic.
The next "problem" is the speed of the PLC (cycle time) if you use not-optimized DB's.

I would also suggest you that you program more with SCL instructions and wit optimized DB'S.

Can you explain a little bit more about your challenge?
Maybe I can write you a example function for moving your data.

regards
CaOd

CaOd

Hello,

that is right at Step7 classic and a S7-300/400.

If you want to move data between a DB and a instance DB it's at the S7-1500 easier with

• optimized DB
• MOVE instruction
• variant input an output 

Then it's easier to program it for a 1500 system.
There are more possibilities to move data as the S7-300, it's also very different between TIA and Step7 classic.
The next "problem" is the speed of the PLC (cycle time) if you use not-optimized DB's.

I would also suggest you that you program more with SCL instructions and wit optimized DB'S.

Can you explain a little bit more about your challenge?
Maybe I can write you a example function for moving your data.

regards
CaOd

 Thanks for the answer, it is helpful.

The only thing I don't understand here is how is then possible that my code is compiling and working in PLCSIM with ET200SP, even though I have used both AR1 and AR2?

I don't need example code for moving data, I just need a fundamental understanding of address registers and how they are related to hardware architecture i.e. different PLCs:)

I have just read the following sentence:

Note: The writing of the address register AR2 in a function block has no influence on the symbolic addressing of block parameters and static local data and vice versa.

in the "Automating with SIMATIC S7-1500" by Hans Berger.

But I am still not sure what exactly that means.

mopS04

hi mrleksandra,

AR2-register was used for the address of the current instance-datablock in the older PLCs.

maybe it is also used therefore in the newer PLC when you don´t use optimal block-access. Then you have also an offset of each value and you need an address-register for it. Have a try and check it.

hope this helps,

regards,

 I have just made a test FB with optimized block-access, and wrote only the following lines of code:

 L 0

SLD 3

LAR2

But the warning remains still.

huggy_d1

Let me get this straight, you want to get rid of a warning AND use the instruction being warned about when using it in a certain way?

Ok, I officially give up as that makes no sense.  Warnings in TIA Portal generally suggest there is a better way to do something.

My projects all compile with warnings.  I have never not once in 8 years of using TIA Portal not created a project without warnings.

Either stop using STL and join the 2000's, or learn how to accept warnings as a fact of life.

 Hello huggy_d1,

Thanks for the advice, but please don't yell at me. I don't have 8 years of experience, that's why I am asking experienced engineers to hear and learn from them. I believe that it should be one of the roles of this forum - to share knowledge, and discuss about different problems with your colleagues. Maybe I am wrong.

Anyway, I found your answer to be helpful.

Best regards from 3-months-experience engineer.