1 Basic Principles of PLC Ladder Diagram Example 2 X0 X1 X2 X3 X4 X0 X1 X2 X5 X3 X4 X5 X6 X7 X10 LOOP1 X6 reverse flow X3 X7 X10 Reverse flow X0 X1 X2 X6 LOOP1 X3 X4 X5 X0 X1 X7 X10 X4 X6 X7 X10 LOOP2 LOOP 2 1.7 Basic Program Designing Examples Start, Stop and Latched In some application occasions, we need to use the transient close/open buttons for the start and stop of equipment. To maintain its continuous action, you have to design latched circuits. Example 1: Stop first latched circuit When the normally open contact X1 = On and the normally Y1 X2 Y1 closed contact X2 = Off, Y1 will be On. If you make X2 = On at this time, Y1 will be Off.
It is the reason why this is called “stop X1 first”. Example 2: Start first latched circuit When the normally open contact X1 = On and the normally X2 Y1 X1 closed contact X2 = Off, Y1 will be On and latched. If you make X2 = On at this time, Y1 will continue to be On because of the Y1 latched contact. It is the reason why this is called “start first”. DVP-PLC Application Manual 1-17