How does the processor identify the location of a specific input or output field device?

• A. By its address
• B. By its physical location on the rack
• C. By its serial number
• D. By its firmware version

Answer: (A)

In PLCs, each input or output point is identified by a specific address within the I/O map. The processor uses that address to locate the data for that device in the input or output image—the internal representation of real-world signals. During each scan, the PLC reads inputs by their addresses and places the values into the input image, and it writes to outputs by their addresses to update the field devices in the output image. This addressing is how the CPU knows where to find or place data; the physical rack position, serial number, or firmware version don’t determine data location and are used for identification or versioning rather than actual I/O addressing.