combinational circuit and sequential circuit

both combinational and sequential circuits have two inputs and outputs..!

Because not all the logic gate have what the circuit needs to complete the operation

A logic probe is used to test and troubleshoot digital circuits by indicating the logic state (high/low) of a particular point in the circuit. A logic pulser, on the other hand, is used to generate a known pattern or pulse at a specific point in the circuit to stimulate and test the behavior of the circuit under different conditions. In essence, a logic probe is for observation, while a logic pulser is for stimulation.

logic circuit