Programming PLC's w C or C++

[BobB]

Always writing code that is "simple enough for the maintenance guys to understand" is very limiting and in the long run inefficient.

But normally required I find.

Many consultants specify ladder fully documented so that it can be easily understood.

With many of the functions available in ladder in many PLCs these days, ladder is not as limiting as it used to be.

How simply can you write code to be easily understood? I guess what the programmer considers really simple and basic can appear to be difficult to others. I use bit counters extensively and find many people just do not understand them. They are very basic of course.

I was roundly criticised by a so called consultant one day for writing a program that only the writer could understand. I DARED TO USE SHIFT REGISTERS!!! My only comment was that if a person could not understand a shift register he should not be reading a PLC program.

I might add that the consultant has a doctorate in Electrical Engineering and is an academic. I think that explains a lot.

GO JESPER!!!! Could not agree more.

 

[RMA]

The ONLY Siemens programming language that conforms to IEC 61131-3 is SCL (confroms to Structured Text). All the other programming methods are Siemens-specific and do NOT conform to IEC 61131-3.

I think you might be a bit behind the times there Jesper - S7-GRAPH is IEC 61131-3 conform as of V5.1 and there's an option you can set to allow ONLY IEC conform programming - most of the consequences of which seem to me to be rather undesirable though!

According to the catalogue both SCL and S7-Graph are PLCOpen certified.

Also according to the catalogue, Hi-Graph is a "konforme Ergänzung" of IEC 61131-3, which I assume means that it's based on the standard, but unlike S7-Graph, you can't set it to work without the extensions. CFC is said to be "angelehnt" to the standard, which I assume means it approximates to it, but explicitly does not follow it.

Neither Hi-Graph nor CFC are PLCOpen certified.

 

[JesperMP]

Thanks for the clarifications Roy.

But I think that people will miss the more "basic" languages such as "Instruction List" or "Ladder" in the list of IEC conformal languages.