Chapter 14 Sequential Function Chart The figure below shows that SFC_A is executed first. SFC_B will be executed after SFC_A is executed, and SFC_A will be executed after SFC_B is executed. User can achieve the jumps by means of the characteristics of transitions. The steps SP_A and SP_B in the example below are used to express the sequential function chart which will be executed. They are preceded and followed by steps. Besides, the transitions RUN_A and RUN_B are declared in the global symbol table.
action INITIALIZE associated with WAIT in SFC_A and the action INITIALIZE associated with WAIT in SFC_B When the program is executed, the step WAIT in SFC_A and the step WAIT in SFC_B are activated, and the are executed. INITIALIZE in SFC_A sets the transition RUN_A to ON during the first scan cycle, and therefore and therefore control is not passed to SP_B . control is passed to SP_A . INITIALIZE in SFC_B sets the transition RUN_ B to OFF during the first scan cycle, When the step JUMP in SFC_A is activated, the action associated with JUMP sets the transition RUN_B to ON, and resets RUN_A to OFF. When RUN_B is set to ON, control is passed to the step SP_B .
Besides, the transition following JUMP in SFC_A is a special relay which is always ON, and therefore control is passed to the step WAIT . Owing to the fact that RUN_A is set to OFF, control is not passed to SP_A . RUN_A will not be set to ON until the action associated with JUMP in SFC_B is executed. The use of WAIT and JUMP in SFC_A serves to set RUN_B to ON, and the use of WAIT and JUMP in SFC_B serves to set RUN_A to ON. WAIT and JUMP in SFC_A and WAIT and JUMP in SFC_B actually have little significance. If the program is applied to an AH/AS series CPU module, users can assign the qualifier P or P1 to the actions associated these steps. Please refer to section 14.2.6 for more information.
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