I & J Codes

When you encounter an I & J code in a Gerber block, you have found an arc command. Arc commands come in two flavors, Full 360 or Quadrant. The Gerber arc command is very complicated, and this section will only briefly describe usage of the Gerber arc.

Full 360 arcs allow the plotter to draw a full circle (360 degrees of arc) in one single command..

Quadrant arcs only allow for an arc to be drawn through a maximum of 90 degrees of arc, never crossing a quadrant boundary. Due to this restriction, I and J arc center offset codes can get away with never having a negative value, even if the offsets are negative!

When in a Full 360 arc (G75), only one command is required to draw a circle. In Quadrant mode, the same circle would require at least 4 Quadrant arcs (G74), because a circle goes through all four quadrants.

Quadrant arcs will always have positively signed I and J values, even if the center offset is actually negative. Full 360 arc center offsets can be signed positively or negatively. A negative I or J is a sure indicator of Full 360 arcs.

M Codes

M codes are used for machine control. Here are the most commonly used:

• M00 - Full machine stop. Commonly ignored by many plotters.
• M01 - Temporary machine stop. Commonly ignored by many plotters.
• M02 - End of Plot.