Hi Guys,
There is an on-line users guide at;
http://www.maniabarco.com/transdown/rs274xrevd_e.pdf
This has some good explanations and definitions of RS-274X parameters as well as RS-274D "D" codes.

I used it as a reference when trying to get legacy designs into Protel from Gerber. Protel will not accept standard RS-274X so you have to manually manipulate the files to import them in the proprietary Protel format, oddly Protel exports in standard format. This is a clever marketing strategy which makes it as hard as possible to transition from one CAD/CAM package to another (he said with sarcasm dripping from his voice).

Dan
  ----- Original Message -----
  From: Steve Gregory
  To: [log in to unmask]
  Sent: Monday, January 27, 2003 6:14 PM
  Subject: Re: [TN] Aperture file format


  Hi Phil!

  Here's some stuff I found that explains more what a *.whl file is. I've run across them quite a bit, and turn them into a text file to import as a aperture list to view the gerbers...I use GC Preview, and Lavenir Viewmate.

  Hope this helps...

  -Steve Gregory-

  Gerber

  Gerber is a format designed by Gerber Scientific for use with their Photoplotters.

  The Printed Circuit industry has adopted it as a standard because of the flexible and reliable way in which it can be used for Photo plotting Printed Circuit artworks.
  The Basics

  Gerber data contains all of the X & Y coordinates of pad positions and the coordinates for the start and end of traces. These are preceded by codes to tell the photoplotter what it should do with these coordinates.

  The two most common instructions are "Flash" and "Draw". To understand these terms it is useful to know a little of the history behind photoplotting.

  In the early days a photoplotter consisted of an Ultra Violet light source which could be turned on and off at will, these are called Vector plotters.

  The light from the source would shine through holes on the aperture wheel to expose the UV sensitive photographic film. These holes are known as apertures and depending on the size of the wheel only 50 or so apertures could be used.

  If more apertures (pad or trace sizes) were required from the design another aperture wheel would be needed. The process of the light turning on and then off through the aperture wheel in a certain position is known as a Flash .

  To produce a trace the appropriate aperture would be chosen and the light would turn on and remain on whilst the head moved around drawing the trace, in much the same way as a conventional pen plotter would do, this is known as a Draw.

  This is obviously a very time consuming process, some plots could take in excess of 1 hour, also designers became very limited by the number (and shape) of the apertures that they could use.

  To combat these restrictions Raster laser plotters were developed. The way in which these machines differ is in the way the film is exposed and the data handled. Before the Gerber data arrives at the Photoplotter the circuit design is converted into a series of dots or Rasterised.

  Then instead of the aperture and light source arrangement as used by the above plotters a Laser is used. The Laser turns on and off very rapidly where the dots are required thus exposing the film. The Laser normally moves from left to right in strokes down the sheet at very high resolutions 3-5000 dpi , a 20" * 24" sheet being fully exposed in less than 6 minutes.

  Because the data is converted into a series of dots and no physical aperture wheels are used any shape can be plotted with no limit on the number of apertures that can be used.

  Formats
  RS274-D.................Requires a separate aperture table
  RS274-X..................Aperture table is embedded in data.




    Hello Technetters,

    I've come across an aperture file that I'm having trouble reading into
    my CAMtastic 2000 software.
    Looking at the file with notepad it has reference to CADAM (40) and has
    the file extension .whl
    Can anyone shed some light on what this is?

    thanks,

    Phil Dutton











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