Variable speed printing for dot matrix printers

Abstract

A variable speed printing (VSP) adaptor for a dot matrix printer which includes a monitoring means having a plurality of devices each capable of assuming one of two states. The monitoring means monitors the state of the pattern data to be printed, and, in the preferred embodiment, the monitoring means comprises a counter which is preset with a number equal to the number of column scans with a dot print line. The pattern data to be printed is scanned in a forward direction, i.e., in the normal printing direction starting at the first print position and the count in the counter is decremented one count for each column data scanned. During the time interval between when this data is latched and the actual hammer actuation, the pattern data is scanned in the backward direction starting at the last print position. Each time the column data for a backward scan is zero, i.e., no dot to be printed, prior to sensing a non-zero column, the count in the counter is decremented one count. The printing operation continues in the interleaved forward/backward scans until the count in the counter reaches a reference level such as zero. Upon sensing this reference level in the counter, a control signal is generated which indicates that the printing of the dot row is complete and initiates movement of the paper to the next dot row position. In an alternate embodiment, the monitoring means comprises a random access storage device.