Abstract

A printer responds to channel commands including coded data received over a channel from a data processing unit by printing characters represented by the coded data using an electrophotographic printing arrangement. The coded data received by the printer is first translated into corresponding graphic codes or addresses by a translate table employing a predetermined translation code, following which the addresses are used to locate sets of character image bits stored within a plurality of character generator modules. Each set of character image bits is used to modulate a laser scan of a printing drum to effect printing of desired characters. Both the translate table and the character generator modules are program alterable, and the data stored therein can be loaded directly from or changed in response to data and instructions from the data processing unit. In addition the locations of the addresses stored in the translate table can be changed to accommodate a new code for the incoming data, and the same address can be stored in more than one location in the translate table so that the same character can be printed in response to different codes of the incoming data. New graphic characters to be added or substituted in the character generator modules are communicated over the channel in a form which includes a code identifying the particular character generator module and locations therein at which a set of character image bits is to be stored and graphic character data which is converted and reformated into the desired set of character image bits. Pages of graphic codes can have minor changes made therein during printing to print multiple copies of various forms. Modification data for each copy and which is communicated to the printer from the data processing unit is employed, as necessary, to modify the graphic codes of each given page on a line-by-line basis, as each different copy of the page is printed.