Using this simple resistor circuit, you can trick your oscilloscope into displayin
g two logic signals on one channel. If you select R2 to be twice R, the scope trace will show one of four distinct analog levels for each possible combination of the states of inputs A and B. Of course, the voltage levels that your oscilloscope sees depends heavily on the current-sourc-ing capability of your digital logic. Because you must use high resistances, this technique has a limited frequency range.