2.1.2. NCO IP Core Intel® FPGA IP Evaluation Mode Timeout Behavior
For IP cores, the untethered time-out is 1 hour; the tethered time-out value is indefinite. Your design stops working after the hardware evaluation time expires. The Quartus II software uses Intel® FPGA IP Evaluation Mode Files (.ocp) in your project directory to identify your use of the Intel® FPGA IP Evaluation Mode evaluation program. After you activate the feature, do not delete these files..
When the evaluation time expires, the output of NCO IP core goes low.