When attributes are created on cells, they become parameters to that cell. Each instance of the cell has a copy of the attribute placed on the node, and the node's attribute can then be set independently of the cell's attribute. In such a situation, the node attribute's value is the "actual" parameter to the cell, and the cell attribute's value is the "formal", or default parameter value.

One example of the use of cell parameters is in the SPICE primitives, where user-defined values (such as voltage) are communicated into the icon for generation in the SPICE deck (see Section 8-4-4).

Another use of cell parameters is to parameterize the size of a transistor in a schematic (or to parameterize the scalable layout transistors in the MOSIS CMOS technology, see Section 7-4-2) The transistor width and length can be defined in terms of the parameter value, allowing a single cell to take on many different forms. By combining these parameters with the interpretive language facility, an arbitrary mathematical expression can be placed on the transistor which combines parameter values to form the exact transistor size .

Inside of the cell, the parameter is shown with its name and default value. To see the actual value from up the hierarchy, create a Java expression with the value "@PNAME" where PNAME is the parameter name. For example, if a cell has an attribute called "heat", you might place a piece of Annotation Text (with the "Annotation Text" command under the "Misc" entry in the component menu) and name it "@heat". Make sure to set its Code to Java. When first defined, the parameter has no actual value, and so appears as "heat not found" . If an instance is created and its "heat" attribute is set to 7, then descending into that cell will show "7".

If a parameter is added to a cell, existing instances of that cell may not get properly updated. To do this, use the Update Attributes Inheritance on Node command (in menu Edit / Properties). To do this everywhere, use the Update Attributes Inheritance all Libraries command.

### Parameter Text

Parameters on cells are not tied to any node or arc. Instead, they float freely inside of the cell. You can select the text and drag it to any location in the cell.

Parameters on instances of cells are placed at the same location as they appear inside of the cell. In schematics, the location of a parameter on an icon is determined by the location of that parameter on the sample icon, inside of the schematic cell.

If you do not wish to see a parameter's text on any instance, select the parameter text inside of the cell, use the Object Properties... command (in menu Edit / Properties), and check "Invisible outside cell".

You can disable the display of parameters on cell instances by selecting them and using the Hide All Attributes on Node command (in menu Edit / Properties). You can force all parameters to be displayed on a cell instance by using the See All Attributes on Node command. To restore default parameter visibility on a cell instance, use the Default Attribute Visibility command.