A cord spool for winding a lift cord for lifting or lowering a window covering wherein the cord spool includes an elongated general cylindrical body with a large diameter end and a small diameter end and a circumferential outer surface of a given length extending therebetween. In one embodiment of the invention, the registered memory module allows asynchronous read and write operations when a clock circuit in the registered memory module is being activated. In order to ensure that the scan line integration time is equivalent to an integer number of illumination source light output periods, at least one of the nominal scan line integration time and the nominal illumination source light output period is adjusted.