Toshiba T2N - Manual (Page 213)

5. Programming Language
200 PROSEC T2N
(2) SFC (Sequential Function Chart)
This is a programming language suitable for process stepping control
(sequential control). Also, it is a language which makes the flow of
control easy to see. Therefore, it is effective for program maintenance
and standardization. SFC program is composed of structure part which
shows the flow of control, action program which shows the operation of
each step and transition condition parts which enable the process to
advance. Action part and transition condition parts are produced by
ladder diagrams. SFC can be considered as an execution control
element for making a program easier to see by arranging the control
processes and conditions rather than a single programming language.
(SFC Structure)
The flow of control advances downward from the initial step and,
when it reaches the end step, it returns to the initial step. A step
corresponds to an operational process, and there is an
actionprogram corresponding to each step. The condition of
shifting from one step to the next is called ‘transition’, and there is
a transition condition corresponding to each transition. When the
immediately preceding step of a transition is in the active state
and the transition condition is ON, the state of the immediately
preceding step is changed to inactive and the next step becomes
active.
Initial step
Transition
Step
Divergence of simultaneous sequences
Divergence of sequence selection
(Transition condition)
(Action program)
End step