One function of a PLC input interface module is to

• A. Accept signals from field devices and convert them into processor signals
• B. Provide power to I/O modules
• C. Decode actuator commands
• D. Store program instructions in memory

Answer: (A)

Accepting signals from field devices and converting them into processor signals. An input interface module is the point where external sensors and switches connect to the PLC. It conditions and level-shapes the incoming signals, provides isolation to protect the CPU from field conditions, and translates various field signal formats (like 24V digital inputs) into the standardized logic levels the PLC processor can read during its scan. This enables the CPU to reliably see the true state of each field device as part of the control logic.

The other roles listed fall to other parts of the system: providing power to I/O modules is handled by the power supply backplane; decoding actuator commands is typically part of the control or output interface flow; storing program instructions resides in the PLC’s memory, not in the input interface.