What Is Ladder Logic?
Ladder Diagram (LD) — commonly called ladder logic — is the most widely used PLC programming language. It was designed to resemble relay logic schematics, making it familiar to electricians transitioning to programmable controllers. A ladder logic program consists of rungs (like the rungs of a ladder) that are evaluated sequentially from top to bottom. Each rung contains contacts (inputs) on the left and coils (outputs) on the right, connected by power rails representing DC power.