Path: utzoo!mnetor!uunet!portal!cup.portal.com!dataxpress
From: dataxpress@cup.portal.com
Newsgroups: comp.lsi
Subject: Re: Posting schematics...
Message-ID: <3947@cup.portal.com>
Date: 18 Mar 88 10:59:46 GMT
References: <915@cfa.cfa.harvard.EDU> <8803112135.AA17866@venera.isi.edu> <3908@cup.portal.com> <920@cfa.cfa.harvard.EDU>
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In reply to:
Re: Posting schematics...
3/16/88 09:25       ward@cfa.harvard.EDU (Steve Ward)

>As I understand it, EDIF allows the
>definition of graphics symbol to plot mapping to be done by the user.
>In other words, EDIF does not provide a specific schematic definition
>methodology such that it defines the graphics plot representation of the
>schematic.  The definition and interpretation of drawing the schematic
>onto paper or whatever is left to the user.  This is really a question,
>since I am not sure my understanding is correct, and I do hope it is
>wrong.  Someone who really knows should comment on this.

A semantic rule of EDIF is that the relationship to SI units and all numeric 
values must be explicitly specified in the EDIF file.  In other words it is 
impossible to specify a coordinate value in EDIF and not know what that 
value is in meters, inches, or whatever unit you like to use.  Thus if you 
create a  schematic in which all your symbols are one inch square, then all 
readers of EDIF will be able to determine that your symbols are one inch 
square.  If they want to plot them scaled down by one half, then that's their 
business.  

The scaling of all values to SI units is specified in EDIF using the 
"numberDefinition" and "scale" constructs within the "technology" construct.  
For example, to specify that all your coordinates are in MILS ( 1/1000 inch ) 
your EDIF file must contain the following:

  (technology
    (numberDefinition
      (scale 1 (e 254 -7) (unit DISTANCE))))

which states that one distance unit is equal to 254 * 10**-7 meters, which 
is one MIL.  Thus, a circle whose diameter is specified in this EDIF file to be 
1000 should be plotted as a circle one inch in diameter (assuming no scaling 
is applied during plotting).

Before EDIF 2 0 0 was published many drafts were released and reviewed by 
CAD and CAE experts from all over the world.  I'm talking about hundreds of
people reviewing over twenty drafts.  It's unthinkable that such a feature as 
mapping numeric values to real units could have been left out and still gone 
unnoticed during the review period.  

John Eurich    dataxpress@cup.portal.com