S7-Graph, S7-HiGraph, S7-SCL Disadvantages

  • Thread starter Adwait A Palsule
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Thread Starter

Adwait A Palsule

Hello all !!

I am a graduate research assistant at RIT and am working with Siemens Simatic system. I would be glad if anyone can list a few disadvantages of teh following programming languages,

Structured Control Language

Daniel Chartier

Hello Adwait;
Boy! do you have a strange way to put your question!
There a 2 disadvantages I can see to using these (and any other) high-level language on any PLC: first the size of the files is much larger (FBs and DBs for Siemens)than if you had programmed the same functions in STL, for example; second, you need these editors installed on any computer on which you wish to upload the program from the PLC, or else be cursed with the STL verion of those blocks.

Now, if you were asking about advantages, I might have talked about the ease (compared to programming in low-level STL) with which you could program sequential logic (S7-Graph), or state-space logic (S7-HiGraph) or high level math and statistical functions (S7-SCL), which is why such languages were included in IEC1131-3. But who is counting?

Hope this helps,

Daniel Chartier

Dobrowolski, Jacek


My opinion about S7-SCL: VERY poor editor (at least version 5.0). There's no on-line syntax check, no syntax highlight, no mechanism for
selecting variables to insert.


Jacek Dobrowolski, M. Sc. E. Eng.
Software Eng.
I'd agree with Daniel,

There are big advantages; Pretty much anyone can read a graph and understand what's it's basically doing, That can't be said of ladder or STL (statement list). It's also very fast to make sequences and you can change them much faster than if they had been programmed in Ladder.

Disadvantages are the size of blocks, you need the software installed on all PC's you want to edit it on and you are somewhat 'limited' to the functions you can use so you have to program some FC's still in Ladder or STL.

Hope this helps

Iain Smith

Donald Pittendrigh

Hi All

HiGraph is a fantastic product for sequence control, it is self documenting and sufficiently "non-programmer" orientated that the control features of the program can be demonstrated easily to someone with no ability in
programming languages. It cannot be compared to trying to explain STL or the "lower level" PLC languages to a "non-programmer".

HiGraph uses a compiler to generate STL code, in fact PLC's in my experience all run STL code and the rest is only the way it is visualized.

Be warned about HiGraph however, it is not possible to recover the HiGraph graphics from the STL, loose the original source files and you are in for a damn hard time, I have been there!!!

Donald Pittendrigh