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Magic Mailing List |
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From: R. Timothy Edwards (tim AT stravinsky DOT jhuapl.edu) Date: Sun Sep 28 2003 - 18:22:55 EDT
Dear Charles, "genericcontact" is basically a stopgap solution to various contact problems in magic. In the "scmos" tech, there is hardly any information regarding genericcontact other than a drc width and spacing rule, which probably aren't valid for any technology. Thus, DRC for any layout containing genericcontact in the default scmos rules should not necessarily be trusted. In Jeff Sondeen's newer techfiles, the genericcontact has a more useful place. Namely, it covers situations where an input file may declare a contact cut, place it in a cell, then use this cell over (say) pdiff and ndiff, which would normally be illegal in magic. In both cases, however, it should be noted that genericcontact defines a contact *cut* instead of a contact area (the idea of a contact area representing both the cut and the layers it connects, called the "residues", is I believe unique to magic, and comes with its own benefits and drawbacks). So where a typical magic contact type will be 4 by 4 lambda, the generic contact will normally be 2 by 2 lambda and require a 1 lambda surrounding of the two residue types. This is true for the scmos techfile, but there are no defined DRC rules insisting upon an overlap of any layer with the genericcontact. The plane on which the contact is defined, called the "home plane", is another issue altogether. That was one of the primary targets of my 7.3 version of magic, which basically ignores the whole "home plane" concept except for some trivial internal record-keeping. There are probably a thousand subtleties to the whole generic contact/generic via story, but the main point to remember is that generic contacts and vias represent the cut only. One consequence is that a row or array of contacts, which can be represented with one rectangle using magic's "normal" contact types, requires a separate 2x2 rectangle of type "genericcontact" for each cut. I hope that clears up most of your confusion. Regards, Tim
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