Several 805x's, e.g. DS89C4x0, allow the boot code to reside in INTERNAL code space, and, subsequently, allow the external read/write memory whether it's BBRAM or FLASH, to be loaded under the control of that internal code, then allows the internal code to be mapped out, i.e. removed from the memory map, thereby allowing the code in BBRAM or FLASH, with the aid of an external flipflop, to become the external program store. There are several ways in which this can be accomplished.

This does, however, require that the designer know something about hardware, which the O/P apparently does not.

RE