S7 ladder & STL

I am using a copy of an old project to make a new project in S7. When I completed the old project I did an Achive to a single file. Then I unzipped it to a new directory to start my new project. It looks like everything is there but now some of the ladder rungs are in STL. I can't seem to get them to change back to ladder. I don't know if this is something I have done or if it could be the S7 updates that I have added. Anyone else have this problem?

I don't know why it's happened, although it may have something to do with any updates you've made, but if the ladder rungs weren't too complicated you may still be able to get them back.

Ladder and function block use a couple of special STL commands to help with the formatting of the graphic display, these are the BLD and NOP instructions. I'm not entirely sure under what circumstances the BLD command is used, but the NOP command is often used for unused inputs to a block. If you make a new file with a few typical networks similar to the old ones you may be able to figure out where to insert these instructions in the old STL version so that it will switch back to ladder.

The display in ladder or FB is on a per Network basis, so even if you can't rebuild every network, those that you can rebuild will then display in ladder while the unrebuilt ones display in STL - may be better than nothing.

Tech support fixed me up. I had a data type wrong in the symbol table. I did a little write up on the problem and what I did to fix it.

Thanks for the help

Oops, I'd forgotten about that one!

This is quite a common problem. In STL there is no type checking done (which under some circumstances can be very useful, always assuming you know what you're doing!). In Ladder and FBD by default type checking is enabled (it can be disabled as shown in your PDF, but most people would not recommend disabling type checking in ladder and FBD). This can lead to the result you had if, for example, you change a variable type in a DB that your ladder program accesses, say from INT to REAL. Even though you haven't done anything inside your program, the next time you open the program to work on it, you'll get a type error and the program will display that network in STL.