Abstract: A system for debugging a processor includes logic circuits for communicating commands and data between a serial input/output port, a trace logic, and the processor. Some embodiments of the debugging system also include a parallel input/output port so that the logic circuits also communicate commands and data between the parallel input/output port, the trace logic, and the processor. The debug system includes a plurality of state machines that read the commands and data from the serial input/output ports. The commands are decoded by a decode logic. Some of the commands, such as commands for reading data from memory, utilize processor intervention and are transferred to the processor for execution. The state machines operate only on a single command at one time so that an active state machine does not accept additional commands until completion of the command that is currently executed.