In some cases it is possible to create a higher resolution than a native one by vertically interlacing graphics (rendering each block of graphics data in two passes). In order to accomplish this, the printer must support a vertical cursor-movement command that uses a resolution at least twice as fine as the native vertical-graphics resolution being used. The Universal Printer Driver accomplishes this by sending the first block of raster data as normal, but during the second pass, the print-head position is incremented in the y-direction by a value that is less than or equal to the height of a single pin or jet. In order to render bitmaps correctly, the Universal Printer Driver requires the number of pins used by the printer for interlaced graphics. If the height of a block of graphics data is less than the height of the specified pins, the Universal Printer Driver will add null graphics data to the block.
An example of this is found in many 9-pin dot-matrix drivers. Typically, a 9-pin printer will support a 240 X 72 dpi resolution as its highest native mode, but also has a vertical-movement command that operates in 1/144 inch. The Uni-versal Printer Driver may support a 240 X 144 dpi resolutions if the driver sets sPinsPerPass to 8 (the number of pins fired in one pass), sets sNPins to 16 (the number of pins fired in two passes), and supports the 1/144-inch vertical command.
For the Diconix 150 Plus printer, the sNPins box contains the value 8; this is the number of jets used by the printer for noninterlaced graphics.
For the HP LaserJet IIP printer, the sNPins box contains the value 1.