The KCE and KHT printhead series have a history control feature built into their driver ICs. This section describes the additional control signals present on these printheads. Please first see Controlling the Thermal Printhead to understand the relationship of the \STROBE, BEO and the data bit in the latch register.
History control is a set of techniques for reducing the pulse width when it is known that a heater element has retained heat from firing on the previous line. If history control is not used, the printer must wait long enough after a line has printed to allow the heaters which fired to cool down to the temperature of the heaters which did not fire. Otherwise, heaters which fire frequently grow hotter over the length of the page, resulting in poor print quality from larger or darker printed dots and possible shorter lifetime due to operating at excessive temperatures. History control uses different pulse widths on a dot-by-dot basis, depending on the heat assumed to be present from having fired on previous print lines.
The conventional \STROBE signal fires all selected heaters for the same amount of time. The printer controller can implement history control by, during a single printed line, loading the printhead several times with different data and briefly firing the heaters, resulting in a total pulse width that varies by dot. The burden is on the controller to compute which heaters are to receive which supplemental pulses. History control as implemented by Kyocera's driver ICs has five \CONT signals, which the printer controller holds low for progressively shorter amounts of time. The driver IC chooses which \CONT pulse width to use for each dot based on that dot's immediate history and the immediate history of the adjacent dots.