Hierarchy of SFC programs
When a child program is stopped, its children are also implicitly stopped.
When a child program is started, it must explicitly in its actions start its children.
A child program is controlled (started or stopped) from the action blocks of its parent program. Designing a child program is a simple way to program an action block in SFC language.
Using child programs is very useful for designing a complex process and separate operations due to different aspects of the process. For instance, it is common to manage the execution modes in a parent program and to handle details of the process operations in child programs.