ABSTRACT
Digital logic circuits can be classified as belonging to one of two categories, either combinational (also called
combinatorial) or sequential logic circuits. The output logic level of a combinational circuit depends only on
the current logic levels at the circuit’s inputs. Conversely, sequential logic circuits have a memory
characteristic, making the sequential circuit’s output dependent not only on current input conditions but also
on the current output state of the circuit. The primary building block of combinational circuits is the
logic gate. The three simplest logic gate functions are the inverter (or NOT), AND and OR. Other basic logic
functions are derived from these three. See Table 1.1 for truth table definitions of the various types of logic
gates. The memory elements used to construct sequential logic circuits are called latches and flip-flops.
