Technology Object Read Access Error

Dear Experts,

I am currently working on my first Motion Control project in Siemens using TIA Portal V15.1. I have encountered an issue and I cannot get to the route cause so I was hoping to call upon your expertise.

I have created Function Blocks for a Speed Axis, Synchronous Axis and External Encoder Axis. I have declared an InOut variable in each FB for the respective Axis TO. The Motion Control commands are also stored in the FB in the Static area. There are various In and Out variables that i use in my program to send commands to the FB and read status from it.

What I am finding is when I call the FB for execution I get a "read access volatile DB area" error. When I navigate to the source of the error from the Diagnostics it references every line of code where I declare a variable contained within the Axis TO (InOut variable), i cannot for the life of me work out why.

Any help would be appreciated.

Many Thanks

Hi,

can you share the project?

Hi ATS-TR2017,

Look if you've the Axis TO (InOut variable) - Declared on the data types of PLC. 

If it's already create, open the FB, right click on Axis TO and Update type.

Trying to help,

Guillem

Guys,

I have attached a copy of the project.

Regards

Guys,

I have attached a snippet of the code from Network 1.

Regards

I usually use InOut var of TO type and I never had that problem.

Does the problem persist if you don't use SCATTER?

What if you "slice" directly the variable in the TO db such as, for example: 

#IO_External_Encoder.StatusWord.%X7

You cannot scatter members of a technology object. You need to save it to a temporary variable and use this for the scatter instruction.

In FC all inputs (IN & INOUT) are used "Copy by references". In FB all INOUT inputs are used "Copy as reference", IN inputs are used "Copy by value".

However, technology objects are always "Copy by reference".

Further information can be found here: Transfer parameter as copy or as pointer

Hi,

Thank you all very much for your help in resolving this. The issue is indeed the SCATTER function. Both methods mentioned above, slice access or transferring to a temporary DWord before passing through the SCATTER function resolve the issue.

Thanks again for your help, it is much appreciated.