Combinational circuit analysis starts with a schematic and answers the following questions:

What is the truth table(s) for the circuit output function(s)

What is the logic expression(s) for the circuit output function(s)

Two types of analyses are possible literal as well as symbolic analysis. Literal analysis is process of manually assigning a set of values to the inputs, tracing the results, and recording the output values. For 'n'' inputs there are 2n possible input combinations. From input values, gate outputs are evaluated to form next set of gate inputs and evaluation continues until gate outputs are circuit outputs. The literal analysis only gives us the truth table.

Symbolic analysis also starts with the circuit diagram like literal analysis. But instead of assigning values, gate output expressions are determined. Intermediate expressions are combined in following gates to form complex expressions. Symbolic analysis is more work but gives us complete information of both the truth table and logic expression.

Now we will consider an example for the analysis of combinational logic circuit shown in Fig. 3.