Alternative Strings

According to IEC 61131-3, only one switch (1-off-n-select) can be made from the transitions. The branch to be run is determined by the result of the transition conditions of the transitions that follow the alternative branch. Branch transitions are processed from left to right. If a transition condition is satisfied, the remaining transitions are no longer processed The branch with the satisfied transition is activated. This results in a left to right priority for branches.

If none of the transitions are switched, the step that is currently set remains set.

Alternative Strings:

If...

Then

If S_5_10 is active and transition condition a is true (independent of b),

then a sequence is run from S_5_10 to S_5_11.

If S_5_10 is active and transition condition b is true and a is false,

then a sequence is run from S_5_10 to S_5_12.