Parts are the basic building blocks of a design. For PCB designs, part may represent one or more physical components; or it may represent a function, a simulation model, or a text description for use by an external application. The part's behavior is described somehow, whether by a SPICE model, an attached schematic folder, HDL statements, or other means.
Parts in PCB designs usually correspond to physical objects—gates, chips, connectors, and so on—that come in packages of one or more parts. "Multiple-part packages" are physical objects that comprise more than one part.
Each logical part has graphics, pins, and properties that describe it. As you place the parts in a package to suit your design requirements, Capture maintains the identity of the part package for back annotation, netlisting, bills of materials, and processes that require it. Parts inherit this information from the package.
You specify packaging information when you create a part. You can also change it in the part editor (using the Package Properties section in the Property Sheet pane).
The parts in a package may have different pin assignments, graphics, and user properties. If all the parts in a package are identical except for the pin names and numbers, the package is homogeneous. If the parts in a package have different graphics, numbers of pins, or properties, the package is heterogeneous.
For example, a hex inverter is homogeneous: the six inverters are identical, except for their pin numbers. A relay, which has a normally opened switch, a normally closed switch, and a coil, is heterogeneous: the three physical parts differ in graphics, number of pins, and properties.
When you place a part on a schematic page, you actually create an instance of the part. A part instance is like a "snapshot" of the part in the library; that is, it inherits all the properties of the library part. Once a part instance is on the schematic page, you can edit the properties of that instance without changing the properties of any other instance. The instance values of those properties supercede the values of any identical properties that exist on the library part. For more information, see Instances and occurrences.
When using multiple-part packages in your design, you must either make all shared pins visible and connect them to power and/or ground nets, or you must make them all invisible, in which case they are connected according to their pin names. See Making power pins visible for more information.
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