Virtuoso XL Layout Editor User Guide

Preparing Instances and Pins in Your Layout for the Virtuoso XL Layout Editor

Preparing Pins for Permutability

If you want to make the instance pins or terminals of a device permutable (exchangeable), you must define the permuteRule property for the device.

You can define thepermuteRule property as

■A property of the symbol master cellview in the schematic

■A property of the device master cellview in the layout

■A property of the symbol instance in the schematic

■A property of the device instance in the layout

■A component description format (CDF) parameter of the device cell

If you define thepermuteRule property on a schematic symbol, that setting overrides any other rule defined in the layout for that instance.

All pins that are not listed in the permuteRule property for a device are fixed (not permutable) by default.

You can set an environment variable, CDS_Netlisting_Mode, to specify the order in which the software looks for the permuteRule property.

The Auto Permute Pins option in the Layout XL Options form must be active for Virtuoso XL to permute pins automatically. Virtuoso XL lets you permute pins manually when the Auto Permute Pins option is not active.

Search Order Variable

To specify the order in which the software looks for the permuteRule property, you can set an environment variable, CDS_Netlisting_Mode,in your .cshrc file or.cdsenv file.

Virtuoso XL Layout Editor User Guide

Preparing Instances and Pins in Your Layout for the Virtuoso XL Layout Editor

If the environment variable CDS_Netlisting_Mode does not exist, the value defaults to

Digital.

Note: The value (Analog, Digital, or Compatibility) must be written with a capital letter.

Virtuoso XL checks for the permuteRule property in a way similar to the way the Assura™ ® verification tools check for this property. However, these tools check permutability rules only in the Layout Versus Schematic (LVS) cellview and in the CDF, while Virtuoso XL checks permutability rules in the symbol cellview and in the layout instance and master cellviews, as well as the LVS cellview and the CDF.

In case of conflict between rules and pins, the rule is ignored and no pin permutation is allowed.

Important

The permuteRule is set as a CDF if the CDS_Netlisting_Mode is set to Analog.

Permutation on an instance by instance basis is not allowed because CDF does not allow instance-based properties. To enable permutation on an instance by instance basis set the AutoPermutePins environmental variable as an instance property.

Syntax

The syntax for the permuteRule property is the same as is used in the Assura Diva verification tools. Two keywords used in the property are p, for permutable, and f, for fixed. For example, the property contents

p(1 2)

defines pins 1 and 2 as permutable, and any other pins as fixed.

Virtuoso XL Layout Editor User Guide

Preparing Instances and Pins in Your Layout for the Virtuoso XL Layout Editor

For example, in the multi-emitter BJT shown here,

C

E1 E2 E3

pins E1, E2, and E3 are permutable; therefore you define the propertypermuteRule as

(p E1 E2 E3)

You can define permutable pins hierarchically. For example, the property contents

(p (p 1 2) (p 3 4))

defines pin sets 1,2 and 3,4 as permutable pins and defines the two sets to be permutable with each other.

Permutable sets can be defined as in this example:

(p (p A B C) (p D E F))

A

B

C

D

E

F

The property contents

(f (p 1 2) (p 3 4))

defines two permutable pin sets as not permutable with each other.

Virtuoso XL Layout Editor User Guide

Preparing Instances and Pins in Your Layout for the Virtuoso XL Layout Editor

Macros

To avoid entering long lists of permutable pins for the permuteRule property, you can use the following macro notations:

■ALL, to indicate all the pins in the cell

(f ALL)

(p ALL)

■Range indications, where pins are numbered or sorted as in bus notations

(f A<0:12> (p A<13> A<14>) A<15:16>)

The notation

(p A<0:3> B<4:7>)

is equivalent to

(p A<0> A<1> A<2> A<3> B<4> B<5> B<6> B<7>)

and states the equivalence of all pins to each other. The notation

(p (f A<0:3>) (f B<4:7>))

states the equivalence between two sets of nonpermutable pins

A<0:3> and B<4:7>

You can also express range indications in descending order

(p A<3:0> B<7:4>)

Setting the permuteRule Property in the Symbol Master

To set a property on the symbol master cellview, follow these steps.

1.From the schematic window, choose Design – Make Editable to make the design editable.

2.Choose Edit – Properties – Cellview.

Virtuoso XL Layout Editor User Guide

Preparing Instances and Pins in Your Layout for the Virtuoso XL Layout Editor

The Edit Cellview Properties form appears.

3.Click Add.

The Add Property form appears.

4.In the Name field, typepermuteRule.

5.Set the Type cyclic field tostring.