Microprogrammable processor control printer system

Abstract

A self-diagnostic printer controller circuit and system may be fabricated in an inexpensive and flexible manner by functionally dividing the tasks of the printer system into separate modules which are intercommunicated through a plurality of buses on a mother board. One of the modules is a central processing unit particularly adapted to performing the required operations in a printer system. The printer system may contain a plurality of additional options, one of which is an internal vertical format unit in which paper instructions may be stored and selectively retrieved by the central processor unit to be used as data to direct the operation of the other modules according to the selected format. The printer has a stepper motor for vertically advancing a printing medium being printed and the VFU includes a format memory for storing information establishing the desired format for printing onto the medium. Vertical advance control means, connected to the stepper motor and to the format memory, are included for accessing vertical format information from the format memory and for causing the stepper motor to advance the medium vertically by a distance established by the accessed information. The VFU also includes circuitry, responsive to a 'direct access' command received from the external data source, for loading into the format memory new vertical format information supplied from the external data source.