Classification of Circuit Components

When one thinks of circuit elements, a myriad of objects immediately comes to mind. These devices include wires, AND gates, transistors, input and output ports, RS-latches, HIGH and LOW signals and so on. For the purpose of this report, objects which are at the digital level and above will only be considered. Therefore, switch level devices such as transistors will not be considered.

One possible way to classify these numerous objects is to consider all the circuit entities at their highest level of abstraction and attempt to group objects which have similar properties under the same base class. From this, three very general classes are formed:

• Component -- All elements derived from this class process input signals and generate output signals to the objects to which they are connected. It is possible for one component to be part of another component. Circuit elements which can be considered as kind of components would include AND gates, RS-latches and random functional blocks.
• Connector -- All elements derived from this class would be responsible for connecting components with other components or with the external world. Each connector is part of a component at some level of abstraction. Since a connector can ``feed'' one or more components via fan-out, a list of components can be considered part of a connector. Some circuit elements which are kind of connectors include wires, and I/O ports.
• Signals -- Objects instantiated from this class are passed from component to component via the connectors. As will be shown later, a list of signals can be considered as part of a wire. This report will consider signals as two entities: a signal value (such as HIGH, LOW or X) and an associated unit of time. Since signals are used almost exclusively during the simulation of circuitry, a detailed analysis of this class will be postponed until the next chapter.

As alluded to above, linked list classes are required for components and signals. As will be shown in the next section, the need will also arise for a linked list class for I/O ports. Due to the current lack of parameterized types in the C++ language, some duplication of code is necessary to create the three linked list classes. Fortunately, the replication of code is relatively small.

 
• The Component Class
  • The Component_List Class
• The Connector Class
• The Wire Class
• The Port Class
  • The Input and Output Class
  • The Port_List Class