Abstract: Apparatus for generating and receiving for analysis multibit digital words, which may vary from one another in voltage level, and which are applied to and received from the pins of an electronic unit under test at different variable clocked rates in response to computer commands. The apparatus includes shift registers each of which is for applying multibit digital words to a pin of a unit under test and which is paired with a receive/compare register for receiving and comparing digital responses from the pin of the unit under test, and Field Effect Transistor (FET) switches, for the real time switching of shift and receive/compare registers alternately into electrical connection with pins of the unit under test. Multiple independent programmable pulse clocks regulate the application of bits to unit under test pins in accordance with computer commands or other designated controls.