Abstract: An apparatus for simultaneously testing multiple integrated circuits includes a sensing circuit associated with each of the tested circuits. Each sensing circuit includes a differential amplifier with its positive input connected to the input of the test circuit, and its inversion input connected to the test circuit output. The test circuit input and positive amplifier input are biased to a selected voltage, and the voltage drop across the test circuit is provided to the amplifier inversion input. Whenever the test circuit is open, intermittently open or highly resistive, the voltage drop across the test circuit exceeds the threshold voltage of the differential amplifier, causing the amplifier to generate a high level logic output representing an open circuit condition. The outputs of the various sensing circuits together form a digital word representative of the condition of all of the test circuits.