[Magic-dev] Method of storing layer information in MAGIC files

[R. Timothy Edwards]

Dear K.S.,

 > For example, if I were to draw an n-diffusion to metal1 contact, the
 > underlying information about the ndiff is deleted. That is to say, if
 > I were to erase the contact, the ndiff which was underneath the contact
 > is gone, as well. I thought I was making a mistake with erasing vs.
 > deletion, but I looked at the actual MAG files, and the ndiff information
 > was gone.

This is an inherent error in the way the paint/erase tables are
constructed in magic-7.2 and earlier.  I fixed this in magic-7.3 such
that if you do "erase m1" on top of the ndiffusion contact, the contact
will be erased but the ndiffusion will remain.

I've found the additional annoyance that if you say "see no *; see ndiff",
you get blank spaces where all the contacts are.  Usually, the intent of
"see ndiff" is to see all areas containing diffusion, including areas
under contacts.  I will have to address this problem sometime soon.

The "usual hack" in versions 7.2 and earlier is to define vias on separate
planes.  This method has a number of drawbacks as well as the advantages,
but does retain the concept of "layers" where there are contact cuts.
None of the standard "scmos" tech files uses this method.

There's nothing wrong with the layer concept in the database; it's mostly
an issue of how the data are presented to and manipulated by the end-user.

						Regards,
						Tim

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| Dr. R. Timothy Edwards (Tim)   | email: tim.edwards at multigig.com     |
| MultiGiG, Inc.	 	 | web:   http://www.multigig.com      |
| 3600 Glen Canyon Road          | phone: (831) 440-0600 ext. 20       |
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