Parallel branches are used in SFC charts to represent parallel operations. Parallel branches occur when more than several steps are connected after the same transition. Parallel branches are drawn as double horizontal lines:
transition before the divergence (1 on this example) is crossed,
all steps beginning the parallel branches (101 and 201 here) are
Processing of parallel branches may take different timing according to each branch execution.
The transition after the convergence (2 on this example) is crossed when all the steps connected before the convergence line (last step of each branch) are active. The transition indicates a synchronization of all parallel branches.
If needed, a branch may be finished with an "empty" step (with no action). It represents the state where the branch "waits" for the other ones to be completed.
You must take care of the following rules when drawing parallel lines in order to avoid dead locks in the execution of the program:
- All branches must be connected to the
divergence and the convergence.
- An element of a branch must not be connected to an element outside the divergence.