Link elements (lines) and their states in LD
Link elements are horizontal and vertical lines within a rung in the LD-editor. A vertical line is intersecting with one or more horizontal lines on each side.
Link state within the ladder diagram
The term "link state" is used as a synonym of the term "power flow". The power flow is the symbolic flow of the electrical power in a ladder diagram and denotes the progression of a logic solving algorithm.
The state of a link element (link or line for short) is denoted as ON or OFF, corresponding to the Boolean values 1 (or TRUE) or 0 (or FALSE), respectively.
The following behavior is valid for a ladder diagram:
The state of the left power rail is considered ON at all times. No state is defined for the right power rail.
A horizontal line transmits the state of the logic element on its immediate left to the logic element on its immediate right.
The state of a vertical link represents the inclusive OR of the ON states of the horizontal lines on its left side. Subsequently, the following state results for a vertical line:
state OFF, if the states of all the attached horizontal lines to its left are OFF
state ON, if the state of one or more of the attached horizontal lines to its left is ON
The state of the vertical line is copied to all of the attached horizontal lines on its right. It must not be copied to any of the attached horizontal lines on its left.
Representation
Example for a rung with horizontal lines and one vertical line:
