Grafcet

Hey all, i was wondering why when i go to make a change to a certain instruction i can't remember what one this problem is from about a year ago i guess.

When i make a change it sais the grafect will changed if we assembled the edits, i was wondering if someone could give me an explanation as to why? and what this means?

Hi Keldog

What are you actually trying to make a change to?
Grafcet is a French acronym for a graphical form of sequence programming which most of us now know as the SFC (sequential function charts) language in IEC61131-3. In all the implementations for Grafcet or SFC I've encountered, the chart itself has always been compiled off-line to an executable file which would then be downloaded to the PLC CPU. In many cases it's possible to view that executable code using a lower level editor such as Instruction List. However, if you make a direct editing change to the executable using IL, there's no way of predicting what effect this would have on the original higher level design. In most cases the editor will warn you and say you are severing all links between the original chart and the current code and you're on your own.

If you do need to modify what the sequence is doing, always go back to the original chart - do not attempt to second-guess the compiler and change a few bits here and there in the compiled code.

Human-written code can be bad; machine-written code can be worse; a combination of human- and machine-written is a guarantee for disaster!

Regards

Ken