1 Basic Principles of PLC Ladder Diagram 1.6 Simplified Ladder Diagram When a series block is connected to a parallel block in series, place the block in the front to omit ANB instruction. X0 X1 Ladder diagram complied into instruction X2 LD X0 LD X1 OR X2 ANB Ladder diagram complied into instruction X0 X1 LD X1 X2 OR X2 AND X0 When a single device is connected to a block in parallel, place the block on top to omit ORB instruction.
T0 Ladder diagram complied into instruction X1 X2 LD T0 LD X1 AND X2 ORB X1 X2 Ladder diagram complied into instruction LD X1 AND X2 T0 OR T0 In diagram (a), the block on top is shorter than the block in the bottom, we can switch the position of the two blocks to achieve the same logic. Due to that diagram (a) is illegal, there is a “reverse flow” in it. Ladder diagram complied into instruction X0 LD X0 X1 OR X1 X3 X4 AND X2 LD X3 (a) AND X4 ORB Ladder diagram complied into instruction X3 X4 LD X3 X1 X2 AND X4 LD X1 X0 OR X0 (b) AND X2 ORB DVP-PLC Application Manual 1-15