What occurs when the count value of a CTU instruction increases?

When the count value of a CTU (Counter Up) instruction increases, it indicates that the counter is currently counting and that the input signal has transitioned to a true state. This action means that the conditions defined for counting have been met, typically through a rising edge or a transition on the input signal which drives the counter's increment operation.

The CTU instruction is designed to keep track of the number of times an event occurs, and when the input becomes true, the counter records this event, thus increasing its count value. The functionality of a CTU instruction is crucial in applications where event tracking, such as the number of parts passing a sensor or a machine cycle count, is important to monitor operations effectively.

As for the other options, they do not align with how the CTU instruction operates. The counter’s behavior is closely tied to the state of the input; thus, an increase in the count value reflects a true state of the input, setting off the counting action.