A semiconductor chip includes an OCC that receives an ATPG test pattern and generates clock pulses in response. An OCC test circuit detects clock pulses of the OCC circuit and provides debug data to test output configurable logic that also receives results from other circuits testing different DUT flip-flops. A clipping test circuit detects ATPG failures due to clipped clock pulses from the OCC by providing pulse-width sensitive flip-flop outputs to DUT I/Os. An IR drop test circuit detects if ATPG failures are due to IR-drop problems in certain flip-flops. A pulse bit manipulating circuit varies the test pattern provided to the OCC and OCC-generated clock pulses. A debug controller connected to test output configurable logic selects between results of the different tests for supply as an output test signal to be compared on-the-fly with expected pattern data on ATE and used to isolate errors on the chip.
