Siemens Step 7 ??

g.mccormick

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I have a potential to do some work for someone that needs some "Siemens Step 7 work" done. I do not know anything about what PLC it is, however, it has been told to me that the customer has the software on a programming laptop to use. They just need some help changing the application.

So the question is how can I quickly learn Siemens step 7 and how hard is it?
 
Assuming it is the older Step7 not TIA, then it is probably an S7300 or 400 PLC.
The things you have to get your head round is the structure of the blocks, there are OB's (Organisation blocks) OB1 can be explained as the main task, although you can write code in there it is really a task that calls other program blocks, other OB's (if called) do many other functions, like interrupts etc.
Program blocks are where you program your code then call them in the OB1 (you can call blocks within blocks), program blocks can be programmed in ladder, STL (like assembler) FBD etc. other blocks of code are FB's (Function blocks), generally these are for creating functions that you can pass variables to/from & re-use as many times as you like, often called from within OB1 or PB's, consider them as the same as AOI's.
Data blocks (DB's) are data areas like an N or F file, however, they can be configured as bits, bytes, words, double words & reals.
S7 is a very powerful language, however, it is so flexible you have to know what you are doing, you can actually download all blocks while in run mode so on-line changes are not limited, this needs care and certain blocks that have been modified must be downloaded first, for example, if you create or extend a data block and modify a program block that uses the extra words then downloading the program block before the data block will halt the PLC if in run mode, the reason for this is the program block is downloaded to the memory, at the end or before the start of main program scan the header to the blocks location is replaced with the new block, so on the next scan the block will be processed & if the DB is not there or long enough it generates an error.
If this is an existing program it is possible that some FB's may be written in STL, although if written correctly will convert to ladder they often have not been written that way so cannot be converted by selecting LAD/STL mode. There are many features too great to mention here, I cut my teeth on Siemens S5 which is almost identical.
I would search for some videos on you tube to familiarise yourself, here is one to start.
https://www.bing.com/videos/search?...B841AE909D1B55266C3AB84&view=detail&FORM=VIRE
 
mind that logic can be blocked and the PLC locked under password... Siemens also allowed the processor to read the online values but not change the program.

What is the change being required?
 

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