Which phase updates the input image table to reflect the status of input devices?

• A. Program scan phase
• B. I/O scan phase
• C. Idle phase
• D. Maintenance phase

Answer: (B)

In a PLC cycle, the input image table is updated during the I/O scan phase. This phase polls all input devices—like switches and sensors—and records their current states into the input image table. That snapshot provides stable data for the program to use during the next phase, where the logic is executed. After the program runs, outputs are updated accordingly. The other phases serve different purposes: the program scan phase runs the user logic using the captured inputs, while idle and maintenance phases aren’t responsible for refreshing input states in normal operation.