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Talking to Photo Plotters
The de facto standard for Photo Plotter data is the Gerber format, more properly known as RS-274D. The term Gerber refers to the Gerber Scientific Instrument company, a pioneer and leader in Photo Plotter manufacturing. Popular variants include Extended Gerber ("RS274X") and MDA FIRE AutoPlot, both of which embed the aperture list information in the file.

RS-274D is a variation on traditional Numerical Control (NC) machine tool languages. It differs from traditional NC formats (i.e. drill data), as far as its use of tool selection codes but is otherwise compatible.

RS-274D data is organized in "blocks". A block consists of a combination of codes:

Tool selection



And, an End Of Block (EOB) character, which only follows a combination of the above codes.

An EOB character is usually an asterisk ('*') or dollar ('$'), optionally followed by a carriage return and line feed.

An RS-274D code consists of a letter D, G, M, X, Y, I or J followed by a numerical value. These codes designate the following:

  • * - End of Block (end of command)

  • D - Select aperture, or set aperture use mode

  • X - Move to X value

  • Y - Move to Y value

  • G - Various setup codes

  • M - Various control codes

  • I - Relative X location for arc center

  • J - Relative Y location for arc center