In Gerber ASCII format, the widths of plotted lines and sizes of flashed pads are defined by the so called D-codes.
This has been explained in detail in Photoplotting Concepts.
System generates separate Gerber ASCII files for each selected layer artwork.
Files for all selected layers are generated in a single batch. The names of these files consist of 8 characters where leading 6 characters are derived from the current database name and the last two are used to code layer number. It is also possible to generate a text file
containing a list of all apertures used in the batch of generated Gerber ASCII files (.ALS).
In addition, it also contains a report file which is automatically displayed and cannot be switched off (.GJR).
For each layer processed in the airgap mode two Gerber ASCII artwork files are generated;
one corresponding to the positive plot and the other to a negative plot.
These may be viewed separately or as a superimposed image.
Files with name suffixes 50+ (negative) must be selected as main file (frame Gerber ASCII file) and positive plot files
selected in frame Gerber ASCII file(superimposed). A single artwork file may be generated having a file name as that of a negative plot.
The airgap image is created by photographically adding these two artwork films.
There are also options to create template output and mechanical plot of the artwork.
In the case of thru holes, the template files, by default, has .GBR extension with the first six letters of
the filename corresponding to the first six letters of the database name and the last two
letters are TM to denote that it is a template file. In the case of buried vias, the file extension is .Gxx where "xx" corresponds
to the sandwitch number
Mechanical plot contains the mechanical details of the file such as dimensions and notes.
By default, the mechanical plot file has .GBR extension with the first six letters of the file name corresponding to the
first six letters of the database name and the last two being 90 for Component Side and 91 for Solder side.
There is also an option to create a file containing list of aperture used (*.ALS) For this file, the first six letters
of the file name correspond to the first six letters of the database name and the last two will be MK to indicate that it is a
mechanical plot file. In addition, it also contains a report file which is automatically displayed and cannot be switched off (.GJR).
Preview of Gerber ASCII files
Generated Gerber ASCII files may be previewed before sending them to the photoplotter.
Before preview, each file must be preprocessed to a special format to facilitate faster redraw.
It is possible to simulate airgap mode output (containing either a Copper plane or a Copper pour area)
by first displaying the Gerber ASCII artwork file for negative film and then covering it with the artwork from positive film file.
These may be viewed separately or as a superimposed image. Files with name suffixes 50+ (negative) must be selected as main file
(frame Gerber ASCII file) and positive plot files selected in frame Gerber ASCII file(superimposed).
