Abstract: A microprocessor is disclosed herein having an external command mode for directly accessing the execution unit, responsive to externally generated commands and instructions. An external instruction path is provided, as well as a conventional processor-driven instruction path. A multiplexer is provided that selects which of the instruction paths is actually supplied to the execution unit. Using the external command mode, the user can examine and modify registers, memory, and I/O space without otherwise affecting their contents. Any instruction executable by the execution unit is executable in the external command mode. Because direct access is provided into the execution unit, there is no implicit updating that would otherwise affect the state of the processor and require saving to an alternate memory. The present invention is implemented with a conventional test access port designed in accordance with the IEEE 1149.