Virtuoso XL Layout Editor User Guide

8

Editing Your Layout with Virtuoso XL Layout Editor

This chapter shows you how to use the Virtuoso® XL layout editor (Virtuoso XL) to edit the placement of components in the layout and how to add additional components. This chapter discusses the following topics:

■Identifying Incomplete Nets on page 207

■Moving Objects Manually in the Virtuoso XL Layout Editor on page 210

■Aligning Objects on page 215

■Swapping Components on page 219

■Permuting Component Pins on page 220

■Using Device Locking on page 223

■Using Automatic Spacing on page 224

■Using Interactive Device Abutment on page 226

■Setting Component Types on page 227

■Using Transistor Chaining on page 233

■Using Transistor Folding on page 236

■Adding Pins to a Layout on page 241

■Assigning Pins to a Net on page 243

■Maintaining Connectivity When Editing a Flattened Pcell on page 244

For information about defining pin groups for external connections (must-connect groups), see “Using Connectivity” (Chapter 12) in theVirtuoso Layout Editor User Guide.

For information about using constraints to restrict the placement of objects, see the documentation for the Cadence constraint manager.

Virtuoso XL Layout Editor User Guide

Editing Your Layout with Virtuoso XL Layout Editor

Information about Virtuoso XL online forms is at the end of the chapter.

Virtuoso XL Layout Editor User Guide

Editing Your Layout with Virtuoso XL Layout Editor

Identifying Incomplete Nets

To view flight lines (lines that show uncompleted electrical connections between component terminals, pins, and shapes in each net), follow these steps.

Note: Turn off the connectivity extractor by

■Turning off the Connectivity Extractor option in the Layout XL Options form

■Setting the extractEnable environment variable to nil in the .cdsenv file

you will not be able to see flight lines.

1.From the layout window, choose Connectivity – Show Incomplete Nets. The Show Incomplete Nets form appears.

Virtuoso XL Layout Editor User Guide

Editing Your Layout with Virtuoso XL Layout Editor

Flight lines appear in the layout window. Whether all incomplete nets or only a subset of them are shown with flight lines depends on the setup of theShow Incomplete Nets form when the command was last used or when the design was last saved. The default is for all incomplete nets to be shown with flight lines.

Note: You can set an environment variable, showIncNetEnable, that causes flight lines to appear as soon as the design is opened. The default setting for this variable is nil, so flight lines showing incomplete nets do not appear until you choose theShow

Incomplete Nets command.

The Show Incomplete Nets form reports how many incomplete nets there were in the design when the Show Incomplete Nets command was initiated.

Virtuoso XL shows all flight lines by default, but you can use the Show Incomplete Nets form to make the display show only the flight lines for the nets you specify or to filter by net name the names of the nets shown.

2.Select the nets to be displayed by clicking on their names in the Incomplete list of nets or by typing the names in the type-in field. You can click on multiple net names or deselect selected names by using Control click. You can select a range of names in the list by clicking on the top name and then clicking on the bottom name with Shift click.

You can display nets that have been put into a class. To create a class use the Tools – Constraint Manager form. In the Constraint Manager form change the Select Entity to Support Entities. Click the Classes button and select Create. In the Create Class form specify the nets to be put into classes and a class name. The class name appears in the list box.

3.Click Apply.

Flight lines for the nets whose names are highlighted in the list of nets are displayed in the layout. The Show Incomplete Nets form reports how many incomplete nets there are in the design and how many are displayed.

Note: The Show Incomplete Nets command only highlights nets that are incomplete. If a complete net is selected it will not be highlighted. To highlight a complete net use the

Connectivity-XL Probe command. If you have selected a complete net and the net becomes incomplete by deleting a path segment, then the net will be highlighted.

Zooming In on Flight Lines

1. To zoom in on the flight lines that are displayed, clickZoom.

Virtuoso XL Layout Editor User Guide

Editing Your Layout with Virtuoso XL Layout Editor

The flight lines and their surroundings are shown enlarged as much as possible depending on how many flight lines are shown.

2.To zoom in on each flight line in turn, clickIndividual Flight Line Segments.

Arrows appear on the form to let you cycle forward or backward through the displayed flight lines.

Virtuoso XL updates flight lines automatically each time you move a component and make or remove a connection.

Assigning Colors to Incomplete Nets

By default, Virtuoso XL uses the colors you assigned to the Layer Selection Window (LSW) entry layers y0 – y9 to show flight lines. If there are more than 10 incomplete nets in the design, the colors recycle. When you choose Show Incomplete Nets, the colors used are the ones assigned when the command was last used or when the design was last saved.