Abstract: An electronic digital processor system including an internal memory, an arithmetic and logic unit, registers, peripheral control circuitry providing an internal mode, an external mode, emulator mode, data paths, and control and timing circuitry. In the internal mode, the data and the commands are stored in the internal memory. In the external mode, the commands which control the operations of the microcomputer are stored in the external memory. In the emulator mode, the user can combine the microcomputer with external devices to emulate a composite system with minimal hardware. The emulator mode would also allow the user to develop software for the composite system.