I want to modify my uc-board to make both internal and external memory software-debuggable. I thought of a von Neumann architecture but dont know how to design it correctly. I planed to get the different modes switchable (monitor-program for downloading, Run external and Run internal). All of these modes can be selected by !PSEN and !EA signals.
!PSEN !EA monitor = 0 1 run ext = 1 0 run int = 1 1