B
Bruce Durdle
According to IEC61131 Table 46, there are three variants on the divergence of sequence. All three use methods to ensure that only one of the divergent paths can be taken.
In the first, there is an inherent left-to-right priority of the transition evaluations. In the second, the priority order is explicitly assigned by numbering each transition. In these two methods, only one subsequent step is possible. In the third, the "user must assure that transition conditions are mutually exclusive". So the Isagraph implementation is only one of the three, and probably the least rigorous.
In the first, there is an inherent left-to-right priority of the transition evaluations. In the second, the priority order is explicitly assigned by numbering each transition. In these two methods, only one subsequent step is possible. In the third, the "user must assure that transition conditions are mutually exclusive". So the Isagraph implementation is only one of the three, and probably the least rigorous.