In a PLC, if there are 16 inputs and 16 outputs, how would the inputs and outputs be labelled?

In a PLC, if there are 16 inputs and 16 outputs, how would the inputs and outputs be labelled?

• A. 0-15 inputs, 0-15 outputs.
• B. 1-16 inputs, 1-16 outputs.
• C. 0-15 inputs, 1-16 outputs.
• D. 1-16 inputs, 0-15 outputs.

Answer: (A)

The labeling uses zero-based indexing. For 16 inputs and 16 outputs, numbering from 0 to 15 gives exactly 16 distinct addresses for each side. This matches how many PLC systems map each input or output to a bit position in a word or register, where the first item is addressed as 0 and the last as 15. Starting at 1 would waste a spot (zero) and isn’t how these I/O sets are typically addressed, so both inputs and outputs are labeled 0–15.

The labeling uses zero-based indexing. For 16 inputs and 16 outputs, numbering from 0 to 15 gives exactly 16 distinct addresses for each side. This matches how many PLC systems map each input or output to a bit position in a word or register, where the first item is addressed as 0 and the last as 15. Starting at 1 would waste a spot (zero) and isn’t how these I/O sets are typically addressed, so both inputs and outputs are labeled 0–15.