A number of weeks ago there were some questions about the Gerber language.
Those made me believe that a lot is not known about this language. To help
undo this, here is:

==========
The Gerber language is wonderful in its simplicity.

It was originally developed by Gerber Systems Corporation for photo plotters
which were used to make the films required for circuit board manufacturing.
Due to a number of take-overs of corporations the language seems now to be
owned by Mania Technologie but I could find no "official" public
documentation on the GERBER Format on the internet.
In these plotters discs were used that had many aperture shapes and sizes
cut in them. The only shapes used were circles ("C"), oblongs ("O"), squares
("S") and rectangles ("R"). Each one of these apertures was given a number,
called a "D-code". 
Behind the disc was a light source and between the disc and the film was a
shutter. If the user wanted to generate a circular image on the film, e.g.
for the location of a test point,  the proper D-code was called up, the
shutter was opened momentarily and "Flash",  the image was transferred to
the film. If that test point needed to be connected to a component, a
circular D-code representing the width of the trace on the board was called
up, the shutter was opened and the film was moved to allow the projected
image to "Draw" the trace on the film.

As in the time this language was developed memory was still expensive, a lot
of effort went into finding methods to minimize the size of the data file. 
All the decimal points were deleted and to understand where they were
supposed to be, in the instructions for the data a command was added to let
the recipient of the data know this by providing the values "m.n". The m
indicates the number of decimals before the decimal point and n indicates
the number of decimals behind the decimal point. Rather than making the
length of each coordinate number equal to m+n, either the trailing zeroes or
the leading zeroes were eliminated. The format statement "FS" includes an L
indicating the leading zeroes have been omitted, a T if the trailing zeroes
have been omitted or a D if the decimal points are included.
The units were also deleted, so an instruction indicating inches or
millimeters, "MOIN" or "MOMM" , was required.
Any aperture that is not a C, O, S or R can be built up from these shapes in
a combination of flashes and draws. The total formation for such an aperture
can be described in a MACRO, which gets its own D-code.

Originally all these aperture descriptions and the special instructions were
contained in the Aperture file and the location information for the
apertures was contained in the Data file. This was the Gerber 274-D format.
At the present time the Aperture file and the Data file have been combined
as per the Gerber 274-X format. 

As the Gerber language comes in the ASCII format, it is readable and
therefore easy to understand and making a file easy to verify. This is
sometimes necessary, as the language has been "improved" by a few program
vendors. Nice for the users of that program, but not so nice when an
improved file gets exported to be interpreted by an interpreter that does
not know about these undocumented "improvements".

A complete copy of the original Gerber language can be found at this
website: http://www.artwork.com/gerber/274x/rs274xrevd_e.pdf, a booklet
worth having on your desk.
=========


Enjoy,
Ahne Oosterhof,
Fine Line Stencil / A-Laser
Beaverton, OR 97005

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------