A CTU instruction's DN bit is true when which condition is met?

A CTU (Counter Up) instruction is used in programmable controllers to count events and store that count as an accumulated value. The DN (Done) bit of a CTU instruction indicates that the counter has completed its counting operation.

When the DN bit is true, it signifies that the accumulated count has reached or exceeded the preset value that has been defined for the counter. This means that the condition where the accumulated value is greater than or equal to the preset value is satisfied, which sets the DN bit to true.

In practical terms, the DN bit indicates that the counter has successfully completed its counting task and can trigger subsequent processes or events within the control logic. This functionality is crucial in applications where counting events is essential for decision-making or process control, allowing the system to respond only after specific thresholds have been met.

Thus, the correct answer accurately reflects the operation of the CTU instruction and the condition that activates the DN bit.