Logic Elements
Richard C. Dorf · 2018
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.