Virtuoso Schematic Composer User Guide

Creating Schematics

Adding Net Expression Labels to Create an Inherited Connection

A net expression defines the default global signal name for the connection and the name of the property that can be used to override that global signal name.

To create an inherited connection, do the following:

■Add a net expression label to a power supply (or wire) in a lower-level schematic, which is described in “Adding a Net Expression Label to a Wire” on page 168.

■Add a netSet property to an instance in a higher-level schematic, which is described in “Adding netSet Properties to Create an Inherited Connection” on page 172.

[@power:%:vdd!]*

You place the net expression on a wire segment that represents the signal. The net expression names the signal in the same way that a wire name names a signal. The default name in the net expression serves to name the underlying signal.

Refer to “Inherited Connections” on page 114 for a description of inherited connections.

This section describes the following:

■Adding a Net Expression Label to a Wire on page 168

■Adding an Inherited Supply Symbol to a Wire on page 169

■Editing a Net Expression Label on page 169

■Changing the Net Expression Label Display on page 170

■Deleting a Net Expression Label on page 172

Virtuoso Schematic Composer User Guide

Creating Schematics

Adding a Net Expression Label to a Wire

To add a net expression label to a wire in a lower-level schematic, do the following:

1.Choose Add – Net Expression.

The Add Net Expression form appears.

2.In the Property Name field, type a property name.

3.In the Default Net Name field, type the name of a global signal.

The net expression label is attached to the cursor. The display shows

[@power:%:vdd!], but when you place it in your design, the default net expression display is vdd!*. The asterisk ( * ) after the net expression label distinguishes it from a regular wire name. The at sign ( @ ) in the net expression label specifies the beginning of a property substitution expression, as [@instanceName]. It specifies how NLP label expressions are interpreted.

4.Drag the cursor into your design and place the label on a wire (or symbol pin in the symbol editor).

Virtuoso Schematic Composer User Guide

Creating Schematics

5.If the label does not automatically attach to the wire, click on the wire you want to want to add the net expression to.

6.Choose Check – Current Cellview or Design – Check and Save to ensure that the signal is updated with the information from the net expression label.

When a net expression label is attached to a wire, the default net name in the expression names the net.

The schematic extractor processes expressions associated with symbol pins only when the extractor encounters an instance of the inherited symbol in a schematic.

You can change the net expression label display using the Options – Editor command. When initially becoming familiar with net expressions, the value [expression] option can be very useful.

Adding an Inherited Supply Symbol to a Wire

Add an inherited supply symbol by placing an instance of an inherited power supply on a wire in a schematic (which is done only once).

Creating a library with inherited power and ground supplies is done only once. In a similar way, regular power supplies can be used instead of wire names to give a global signal name to a net. Inherited power supplies can be used, instead of net expression labels, to assign a net expression to a net.

To place an instance of an inherited power supply on a wire in a schematic, do the following:

1.In the schematic editor, choose Add – Instance.

2.Place an instance of an inherited power supply symbol on a wire.

[@prop:%:vdd!]*

3.Choose Check – Current Cellview or Design – Check and Save to ensure that the signal is updated with the information from the inherited supply symbol.

Editing a Net Expression Label

To edit a net expression label, do the following:

Virtuoso Schematic Composer User Guide

Creating Schematics

1.In the lower-level schematic, select the net expression label.

2.Choose Edit – Properties – Objects.

The Edit Object Properties form appears.

The Evaluated Name field contains the result of evaluating the net expression for the current descend path of the window.

3.Change the Property Name, Default Net, Height, Font, or Justification value of the net expression label.

4.Click Attachment to reattach the label to the new wire or pin, if required.

5.Click OK.

Changing the Net Expression Label Display

To change the net expression label display so that you can see the value, property, or expression, do the following:

1. Choose Options – Display.

Virtuoso Schematic Composer User Guide

Creating Schematics

The Display Options form appears.

2. From the Net Expression Display cyclic field, choose one of the following:

The value option implies the resulting signal name from the evaluated net expression for the current hierarchical path. The hierarchical path is the instance path that was descended to get to this level.