Siemens SIMATIC PCS7 Manual page 125

Rules of syntax
Restrictions
Batch flexible , Manual
C79000-G7076-C650-02
Certain restrictions apply during the creation of the recipe topology and the
recipe editor complies with them automatically.
The SFC standard stipulates that two transitions and two steps (AF) are not
permitted to succeed each other in the operational sequence.
All of the remaining restrictions derive naturally from the handling or are
locked out by means of grayed-out menus.
Note
The SFC standard even permits syntactically incorrect structures, such as an
alternative branch with a parallel junction (unreachable SFC) or a parallel
branch with an alternative junction (unsafe SFC).
Since this results in undesired or non-useful sequences during on-line
execution, the recipe editor of BATCH flexible will only allow syntactically
correct structures.
Recipe creation
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