Chapter 14 Sequential Function Chart After STEP_1 and STEP_2 are activated, Tran3 will be evaluated. When Tran3 is true, STEP_1 and STEP_2 become inactive, and STEP_3 becomes active. Convergence of sequence selection A convergence of sequence selection is shown below. The characteristic of a convergence of sequence selection is that the convergent steps have their own transitions. When one transition is true, the next step becomes active. If there is another convergent step which is activated, the step will be active until the transition following the step is true. When the transition is true, the step following the transition becomes steps following the convergence may be activated.
If users use a convergence of sequence selection in a active. Consequently, if a convergence of sequence selection is used in a sequential function chart, several sequential function chart, they have to make sure that the program is not confused. When Tran1 is true, STEP_1 becomes inactive, and STEP_3 becomes active. If Tran2 is true, STEP_2 will be inactivated, and STEP_3 will be activated again. 14-11