"Indirect Addressing" in Step 7 Basic v10.5 SP2

For those of us who appreciate and harness the power of indirect addressing in Siemens S7 300 and 400 level PLCs, we were sad to hear that this functionality was not supported in the same way for the new Step 7 Basic software for S7-1200 PLCs.

As of Service Pack 2 for Step 7 Basic 10.5, however, Siemens has added array indexing functions that get you closer to indirect addressing. They are called "FieldRead" and "FieldWrite". Essentially, they are functions that allow you to read and write to specific indexes in an array.

Here are a couple tips and tricks to using these new functions.

First of all, these blocks are not yet available in the "Instructions" panel with the other standard instructions. In order to use these functions, start by dragging an empty box instruction into your ladder rung. From the drop down menu, the last two items listed will be FieldWrite and FieldRead.

Second, pressing F1 to get context help while the block is selected will NOT display the help file for these new blocks. The help files do exist, but they take an extra step to find for now. Start by opening the help panel from the Help menu (Show help). From the help panel, select Readme -> Readme STEP 7 -> Programming a PLC. In the middle of the bulleted list, you will find the help files for "Read field" and "Write field".

Even without formal indirect addressing, these functions at least let you leverage the usefulness of arrays. I expect these functions and help files will be integrated as normal instructions on the next version.

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