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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.

I2C: Inter-Integrated Circuit
The inter-integrated circuit (I2C) is a synchronous bi-directional serial bus which provides a simple, efficient way for data exchange between devices at up to 100Kbit/s. The maximum communication distance and number of devices that can be connected is limited by the maximum bus capacitance of 400pF.

  • I/O: Bi-directional Input and Output Port Pins

  •     I: Input Only Port Pins

  •   O: Output Only Port Pins

Bi-directional Input and Output (I/O) ports couple the microcontroller to external devices. This interface can operate in parallel or serial form and is usually digital (0 to +5Vdc) logic. Parallel interfaces allow I/O data transfer of eight bits at a time to parallel ports on the microcontroller. The technology is typically used to transfer data between the microcontroller and the external logic it controls.

IC: Input Capture (Timer Function)
The input capture (IC) mechanism of a timer can be used to detect the time of an event or measure the period of an input signal. When the selected edge occurs, the current value of the free-running counter is captured by the input capture register, which can later be read by the CPU. This is the timer mechanism typically used in the timing of external events.