Abstract: A system for processing data incorporates a central processing unit and a microprocessor serving as a controller together with associated logic for controlling operation of an attached device such as a serial or line printer. Data is transferred from the microprocessor to the printer by a cable having a number of wires, reduced in number from the number required if printer is directly attached, and involving a multiplexed data transfer operation with storage latches provided in the printer for storing character image information and printer function information. Increased reliability is realized by a repeat cycle operation of the microprocessor wherein significant image or function information is sent to the printer in a succession of repetitive cycles, thus insuring accurate operation of the relatively slow magnets and driving elements in the printer.