Introduction to Digital Systems: Modeling, Synthesis, and Simulation Using VHDL

1.4 STANDARD LOGIC DEVICES

Many commonly used logic circuits are readily available as integrated circuits. These are referred to as standard chips because their functionality and configuration meet agreed-upon standards. These chips generally have a few hundred transistors at most. They can be bought off-the-shelf, and depending on the application, the designer can build supporting circuitry on a PCB (printed circuit board) or breadboard. The advantages of using standard chips are their ease of use and ready availability. However, their fixed functionality has proved disadvantageous. Also, the fact that they generally do not have complex functionality means that many such chips have to be put together on a PCB, leading to a requirement for more area and components. Examples of standard chips are those in the 7400 series, such as the 7404 (hex inverters) and 7432 (quad two-input OR gates).