In a ladder logic program, there is no physical conductor that carries the input signal through to the output. Each rung in the ladder diagram is a program statement. This program statement consists of a condition or sometimes conditions, along with some type of action.. See the Logix 5000® Controllers Program Parameters Programming Manual, publication 1756-PM021. The examples in this chapter use two simple instructions to help you learn how to write ladder diagram logic. The rules that you learn for these instructions apply to all other instructions.
As an introduction to ladder diagrams, consider the simple wiring diagram for an electrical circuit in Figure 5.1a. The diagram shows the circuit for switching on or off an electric motor.. ming language, is ladder logic. Using examples, the language is developed from the electromechani al relay system-wiring diagram. After describing the basic symbols for the various processors covered by this text, they are combined into a ladder diagram. The subsequent section details the process of scanning a program and accessing