Abstract: The keyboard, printer and recording means are peripheral units under the control of a microprocessor including a programmable read-only memory from which appropriate control instructions are derived. Control signal sequences for operating the word processing system are the result of addressing of the read-only memory in accordance with the sensed status of the attached peripheral units and a priority schedule. The peripheral units operate semiautomatically in response to control instructions to execute a commanded function.Control instructions fall into various classes for controlling peripherals, determining the status of peripherals or performing internal operations within the microprocessor. The format of the next address or sequence of addresses to be applied to the read-only memory is dependent on the class of the prior control instruction or the response of a peripheral unit to a particular control signal.