Truth tables are a way of figuring out how a particular digital circuit will respond to different inputs. Truth tables have two distinct parts: each left hand column is labeled with the name of one of the inputs, each right hand column is labeled by a piece of the circuit whose output is to be determined. To fill in a truth table, you begin with the lefthand columns and make one row for each possible combination of the values for the inputs. Then, for each row of the table, using the values in the left hand side and the logic of the circuit, you can fill in the appropriate values in the right-hand sides. Let’s try an example. Here is the machine we’ll work with:
