A METHOD AND APPARATUS TO MEASURE AND DISPLAY DATA DEPENDENTEYE DIAGRAMS

A method and apparatus to draw eye diagrams of multi-valued signals that remove non-data dependent effects is disclosed. An exemplary method includes collecting event counts at variable bit offsets, desired time offsets within one or more bit periods and desired voltage offsets within a voltage region of interest; removing non-data dependent effects from the collected event counts; generating a composite diagram of the desired time offsets within the one or more bit periods of interest and desired voltage offsets within the voltage region of interest; and displaying the composite diagram. An exemplary apparatus includes a windowed comparator operative to receive an input signal and generate an output signal having a first value if the input signal is within a desire d voltage region; a sampling device, coupled to the windowed comparator, operative to sample the output signal and generate a logical signal at desired time intervals; an event array counter, coupled to the sampling device, operative to generate a count value signal representing the number of sampled inputs within one or more desired time offsets and the desired voltage regions; and a trigger processing circuit, coupled to the event array counter, operative to generate a bit offset signal that controls the counting of the event array counterin response to a test pattern signal.