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Create a new Constraint Group or Constraint Class ?

Cailloux

When in Constraint Manager, Physical Domain, one can create a new Physical Constraint Class defining specific attributes for a custom rule set. One can then assing this new rule set to a set of nets. To do that it is instructed to create a new Net Class with menu Objects > Create > Net Class. Also on that same menu is available Net Group. Both options create a group that appear in the Constraint Manager Objects Name Column. I have triied both  options and cant really see the difference. 

The Question: What is the difference between creating a Net Class and a Net Group ?  What are the implications ?

Thanks for your help.

  • The general differences between a Net Class and Net Group are:

    • A Net Class is group of nets specific to a particular domain (Physical, Spacing and Electrical)
    • A Net Group is a group of nets that common across all domains

    You could create a common Net Group then assign a Constraint Set to drive basic rules:

    • Net Group NG1 could have a Physical Constraint Set assigned in the Physical domain
    • Net Group NG1 could have a Spacing Constraint Set assigned in the Spacing domain
    • Net Group NG1 could have a Electrical Constraint Set assigned in the Electrical domain

    Implications?  Constraint Region Rules and Class to Class Rules cannot be assigned to Net Groups

    • Physical domain: You can specify Physical rules for a Physical Class inside and/or outside of a specific Constraint Region.
    • Spacing domain: You can specify Spacing Class to Class rules when different Spacing Classes come in contact with each other inside and/or outside of a specific Constraint Region.

    In addition, Net Classes are domain specific groups so if you wanted to have one larger group of nets to control Spacing rules and a sub-set of those nets to control Physical rules it can be easily done with Net Classes.

    Think of Net Groups as a higher level group of objects to organize interfaces.

    Hope this helps,
    Mike Catrambone

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