Difference between Attatch or reference a library, when creating libraries.

When you attach a technology library, it will use it directly for designs in your library. When you reference a technology library, it actually compiles a local technology library into your own library and adds a reference to the technology library.

Initially these will have the same effect, but if you use "reference" then it means that you have the ability to add incremental data to your own library's tech database. For example, you can add additional layers, constraints (e.g. constraint groups with modified rules), via definitions and so on. You cannot do that if you use attach. If you don't need to add any of these incremental technology database features, then using attach probably makes more sense as it avoids accidentally defining something locally that you didn't mean to.

Andrew

Thanks for such quick reply.

so if i just plan to do cell-level work, both shall be fine, and inadvertent modification of the orignal lib will be prevented?

if i do want to modify cells in the original lib, what should i do then?

This is nothing to do with editing cells in either library. You can edit cells in either the library you are creating or the library that is referenced or attached (assuming you have permissions to do so).

This is specifically about the technology database (which is stored in a file called tech.db) in any library that is not attached to another library. I was specifically talking about making technology changes to your own library - you can only do that if you've referenced another technology library or have compiled a tech file locally into your own library.

Andrew.

Thanks. Does this mean if I want to use the foundry's technology, I'd better choose to attach to a library? If I only use virtuoso to do simulation and don't make changes to tech.db file, it makes no difference, right?