Siemens S7 data block - String

[Safes]

Hi,

I am trying to access stings in Data Blocks with "OPC Scout". However I can access only a few of the DBs. For example I can access DB 20 and DB 28 but not 19. What is the reason?

More detail: OPC Scout shows the aviable address from 0 to 31 for accessable DBs, and 0 65656 for not accessable DB. I think it is not logical too. Why may DBs differ from each other? if not why OPC shows different values for different DBs and I can not access some of them?

Any help??

Thank you =)

 

[Knoxij]

Without looking into it further I can't be sure, but I believe you might be dealing with what SIEMENS refers to as "Instance Data Blocks" or data blocks that are created and used only for storing data for a particular instance of a function. Some of your data blocks would be storing data for other reasons (recipes, formulas, alarm setpoints, etc.).

You might want to look into that area to see what the different data blocks are being used for and check to see if there is some pattern to that.

Next time I head by our PLC lab, I will look into it and see if my thoughts hold any water.

Hope that helps.
Knox