Design of Combinational Logic Circuit Prober

Abstract

The objective of this paper is to design and implement a logic circuit prober to display truth tables of a three input combinational logic circuit. The truth table is to be as “1” and “0” on an ordinary 60 MHz oscilloscope. This paper meets this objective by using Lissajous Patterns to plot a “0” or a “1” on the oscilloscope screen. To plot a “0” on the oscilloscope screen, two sinusoidal signals in quadrature are supplied to the two inputs of the oscilloscope with the scope set to X-Y mode. To plot a “1” on the oscilloscope, only the signal to the Y input is allowed to reach the oscilloscope screen. To display all the 32 patterns required to obtain a three input truth table, two staircase waveforms are employed. The staircase waveforms, one eight-step and the other four-step, are added to the two sinusoidal signals to shift the patterns along the X and Y directions to produce all the 32 patterns.