Which PLC component receives signals from field devices and provides binary state to the CPU?

• A. Input module
• B. Output module
• C. Power supply
• D. CPU

Answer: (A)

Interfacing field devices to the CPU is about bringing real-world signals into the PLC in a safe, readable form. The input module directly handles those field signals. It takes signals from sensors and switches, performs any necessary conditioning, and converts them into binary values that the CPU can read as discrete inputs. This is what lets the program see on/off from each device. The CPU doesn’t read raw field signals directly; it relies on the input module to present clean, usable data. The output module does the opposite, sending control signals from the CPU to actuators; the power supply provides power, and the CPU executes logic but doesn’t interface with field devices without the input module.