In a PLC, what is the function of a ladder logic rung?

• A. It stores data for later use.
• B. It displays the current status of outputs.
• C. It represents a control path with inputs and outputs performing logic to control devices.
• D. It generates random numbers for tests.

Answer: (C)

In ladder logic, a rung represents a control path from the supply (left rail) to an output coil (right side). It contains input conditions—like normally open or normally closed contacts, timers, or other logic elements—arranged in series and/or parallel to form the path. When the conditions on that path are satisfied during the PLC scan, the rung completes the circuit and energizes its output coil, turning on the connected device. If the conditions aren’t met, the output stays de-energized. This mirrors how a real electrical control circuit is wired, but in a form that the PLC can execute step by step, evaluating each rung to decide which outputs to drive.