Method and apparatus for automatically determining the style printhead installed in a laser printer

A laser printer is provided having an automatic printhead identification system for use in a family of laser printers that are compatible with more than one model of printhead. For example, a single laser printer model can be made so that two different printheads can be successfully used, so long as the printer system knows which laser printhead has actually been installed. To detect which printhead has been installed, the printer operating system provides a reference clock signal having a pre-determined frequency, which dictates the rotational speed of the motor. Once the motor has achieved a ""lock"" operational speed, the printer measures the scan rate of the faceted mirror by detecting the time interval between pulses of the ""HSYNC"" signal. The HSYNC signal is sent to a ""divide-by-n counter"" circuit which divides the pulse frequency of the HSYNC signal, thereby increasing the time interval (by a factor of ""n"") that must be sensed by the system to determine which printhead is in fact installed. So long as the HSYNC ""lock"" frequency is different between the various models of printheads that are compatible with a particular model laser printer, the principles of the invention can be used without adding any extra hardware sensors, signals, or memory addresses and detecting codes.