Using background modes for testing, debugging and emulation of microcontrollers

The Background Mode of operation for the M68HC16 and M68300 families of microcontrollers has provided a method whereby an external host development system can take control of the microcontroller causing it to execute certain elementary commands. As shown here, a more complex system can be built using the Background Mode as a base to form an inexpensive, yet capable, emulation system. The addition of a bus state analyzer and appropriate software can further enhance a host development system's usefulness without significantly impacting the complexity of the emulation/debugging system. Most importantly, the Background Debug Mode allows the actual microcontroller in the target system to emulate itself providing, perhaps, the most accurate form of emulation.