Abstract: Apparatus for processing a digital raster scan signal for use by an electrostatic printer having a print cartridge with an ion deposition matrix composed of sixteen drive electrodes intersected by 128 finger electrodes is described. A digital input signal, representing a line of raster scan data, is reformatted to be compatible with this print cartridge. This is achieved by reformatting the signal into sixteen data groups, each containing 128 bits and storing at least sixteen data groups at any one time in a memory. A motion control circuit responds to signals from the memory circuit, from the rotation of the drum and from paper sensors to effect scanning of the ion deposition matrix in a timed sequence. One of the drive electrodes and all 128 finger electrodes are energized by one data group at any one time to effect ion deposition as the drum rotates, then the next drive electrode and the next data group are energized. This is repeated until the entire matrix is scanned.