Does anybody know if there is a program for build Grafcets for project design and documentation phase?

 

Dia has a grafcet mode, but I've never actually done anything serious with it. I find that I can usually just draw grafcet (and state) diagrams using the drawing editors in word processors (e.g. OpenOffice, MS Word, etc.). It's not hard, and it allows the drawing to be integrated into a document with other information.

If you are doing this, it's best to do the drawing and then write the PLC program. If there are any design changes, then you need to update the drawing as you go along. Trying to create a grafcet drawing from a PLC program after the fact is usually very difficult, because the program may not be written in a way that fits the grafcet model.