The Excellon format is widely used to drive CNC drilling and routing machines during printed circuit board (PCB) manufacture. It is a variant of the EIA RS-274-C standard. Only the storage of circles is possible.
The Excellon format can only store circles for a single layer. No other layer information can be stored. The active layer is always stored or loaded. The handle of the load/attached/update command is identical to the Gerber format. `Load´ will add the file contents to a new cell; ´attach´ will load it into the currently displayed cell; ´update´ will replace the active layer in the currently displayed cell.