The “microprocessor revolution” is continuing to be propelled along by advancements in process technology. The process advancements are allowing greater device densities, which in turn are permitting increased functional integration. The microprocessors of yesterday are giving way to the microcomputers of today.The microcomputers are considered to be the integration of a “System” on a “chip” of silicon. They contain mask programmed ROM, RAM, a timer, external interrupt hardware, on board clock oscillator and programmable Input/Output lines. Some are expandable to include off-chip memory and peripherals.To take the “revolution” one step further, a new microcomputer has been created to accomplish further levels of integration for unique control situations. The need to interface with the control environment and its impact on custom integration is the prime consideration for the architecture of the Motorola MC6805 single chip microcomputer. The 6805 is designed to help bridge the gap of design time and investment capital, that exists between standard microprocessors and custom designed controllers.