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We've shown that it's possible to preview our files prior to production using freeware viewer programs. If you run into problems, it's a good idea to directly view the data files themselves using a text editor.
Let's look at two simple files used to produce the tutorial example. One is the Gerber data for the outline layer while the other is the NC drill data in Excellon format.
Gerber Data for the Outline Layer
The data contained between the percent signs (%) define the setup and aperture information embedded in the RS-274X file. The section of the header with %FSLAX24Y24*% is known as the format statement. In this example, we have indicated that we are using leading zero suppression, absolute coordinates, and m.n=2.4 for both the X and Y axis. The line %MOIN*% is a mode parameter indicating that we are working in inch units. The line %AD*% indicates the beginning of the aperture definitions list. These apertures are the embedded "mass parameters" generated per the Gerber specification. Code D10, with a circle aperture and 1 mil diameter, can be seen near the top of the file. G54 is a command telling the photoplotter to change apertures (in this case to D10) before beginning the plotting process. The plotting information is contained after the header. G1 tells the photoplotter to move linearly from the present location to the specified XY coordinate. D2 tells the photoplotter to turn the light source off while D1 indicates that the light source should be turned on. M2 indicates the end of the program (file end).
Now let's examine the Excellon-formatted NC drill information for the board.
Excellon Data for the Entire Board
M48 indicates the beginning of the program (file) header. There are two tool codes specified for this job. T1 is a circular "aperture" (a round hole to be drilled) with a size of 0.028 inches (28 mils). T2 is a 32-mil hole. M47 defines the file name. G05 switches the machine to drilling mode. M72 indicates that the coordinates are in imperial (inch) units. The tool is selected with the T code, moved to the specified XY coordinate, and drilled. The next tool is picked and moved to all of its listed coordinates. The program (file) ends with the M30 command.
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