Which of the following statements is true about discrete I/O in programmable controllers?

• A. It handles digital on/off signals
• B. It handles analog continuous signals
• C. It handles power supply events
• D. It handles network protocols

Answer: (A)

Discrete I/O in programmable controllers deals with binary on/off signals. It reads or controls devices that have two states, like a pushbutton being pressed (on) or a limit switch closing (energized). Discrete input modules sense these digital transitions, and discrete output modules drive devices such as relays or indicator lamps. This differs from analog I/O, which handles continuous signals that vary in value (like 0–10 V or 4–20 mA) to represent a range of measurements. Network protocols are about communication between devices and aren’t themselves the discrete I/O signal type, though I/O data can be transmitted over a network. Power supply events aren’t the I/O signal type either; they’re monitored separately from the discrete on/off signals handled by discrete I/O.