What occurs during each program scan cycle?

• A. The processor reads inputs, then energizes or de-energizes outputs according to the user program.
• B. It compiles the ladder diagram.
• C. It erases memory.
• D. It powers down modules.

Answer: (A)

The sequence of actions in a PLC scan cycle begins with reading the input signals and capturing their current states. Next, the processor runs the user program using those input values to determine which outputs should be on or off. Finally, it updates the outputs by energizing or de-energizing the output modules to reflect the program’s results. This cycle repeats continuously, providing a consistent, real-time response to changes on the input side. Compiling the ladder diagram happens beforehand, memory isn’t erased during normal operation, and modules aren’t powered down as part of the scan.