What is the purpose of the Done bit on timer and counter instructions?

• A. It indicates that the timer or counter has completed its condition
• B. It stores the preset value
• C. It energizes the output
• D. It resets the timer

Answer: (A)

The Done bit is a completion flag from timer and counter instructions. It goes high when the timer has counted to its preset value (for a timer) or the counter has reached its target count (for a counter). This flag isn’t where the preset value is stored, nor does it drive an output by itself—it's simply indicating that the operation finished. Programmers use the Done bit to trigger subsequent actions, latch a state, or advance to the next step in a sequence. It remains true until the timer or counter is reset (or the rung condition clears it), which is why you can rely on it to know when the timed or counted operation is complete.