Hi Pavel,
with change detection, you can automatically trigger your software application to perform a digital read operation upon a digital change of state. The digital I/O module notifies the software application when this event occurs, so no polling is necessary. Using change detection, you can monitor for digital events with minimal processor usage. No polling is necessary, because the digital I/O module generates an interrupt to automatically "wake up" your application.
You can configure change detection in DAQ Assistant or directly in LabVIEW. Specify short Time-out if you want to stop waiting and go further in program execution.
Pavel