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Computer Aids for VLSI Design Steven M Rubin Copyright 1994 Appendix B Caltech Intermediate Format Caltech Intermediate Format CIF is a recent form for the description of integrated circuits Created by the university community CIF has provided a common database structure for the integration of many research tools CIF provides a limited set of graphics primitives that are useful for describing the two dimensional shapes on the different layers of a chip The format allows hierarchical description which makes the representation concise In addition it is a terse but human readable text format CIF is therefore a concise and powerful descriptive form for VLSI geometry Each statement in CIF consists of a keyword or letter followed by parameters and terminated with a semicolon Spaces must separate the parameters but there are no restrictions on the number of statements per line or of the particular columns of any field Comments can be inserted anywhere by enclosing them in parenthesis There are only a few CIF statements and they fall into one of two categories geometry or control The geometry statements are LAYER to switch mask layers BOX to draw a rectangle WIRE to draw a path ROUNDFLASH to draw a circle POLYGON to draw an arbitrary figure and CALL to draw a subroutine of other geometry statements The control statements are DS to start the definition of a subroutine DF to finish the definition of a subroutine DD to delete the definition of subroutines 0 through 9 to include additional user specified information and END to terminate a CIF file All of these keywords are usually abbreviated to one or two letters that are unique B 1 Geometry The LAYER statement or the letter L sets the mask layer to be used for all subsequent geometry until the next such statement Following the LAYER keyword comes a single layer name parameter For example the command L NC sets the layer to be the nMOS contact cut see Fig B 1 for some typical MOS layer names NM nM OS met al NP ND NC NI NB NG



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