1 Basic Principles of PLC Ladder Diagram The order of the instructions: 1 LD X0 2 OR M0 3 AND X1 4 LD X3 AND M1 ORB 5 LD Y1 AND X4 6 LD T0 AND M3 ORB 7 ANB 8 OUT Y1 TMR T0 K10 Explanations on the basic structures in the ladder diagram: 1. LD (LDI) instruction: Given in the start of a block. LD instruction LD instruction AND block OR block The structure of LDP and LDF instructions are the same as that of LD instruction, and the two only differ in their actions. LDP and LDF instructions only act at the rising edge or falling edge when the contact is On, as shown in the figure below. Rising edge Falling edge X0 X0 OFF ON OFF Time OFF ON OFF Time 2. AND (ANI) instruction:
A single device connects to another single device or a block in series AND instruction AND instruction The structure of ANDP and ANDF instructions are the same. ANDP and ANDF instructions only act at the rising edge or falling edge. DVP-PLC Application Manual 1-9