The Simple ladder diagram comprises two vertical lines that represent the power rails. Circuits are connected as horizontal lines between these two verticals, i.e., the ladder's rungs. Certain conventions are followed when drawing a ladder diagram. The vertical lines in the chart represent the power rails that connect the circuits. The power is assumed to flow from the left vertical across a rung. Each rung of the ladder shows a single control operation. A Simple ladder diagram is read from top to bottom and left to right. The scanning motion used by the PLC is depicted in the figure. From left to right, the top rung is read.
