Some changes needed:

/CS(NVRAM) -> GND
/RD(NVRAM) -> PSEN

Since internal Flash + external NVRAM < 64kB, there is no need to switch the EA pin.

Nevertheless you can do it, e.g.:

P1.7 -> /EA


But then no lock bits can be set to be able to change EA after reset.
Also the switcher routine must be in this area of the NVRAM, which was always outside the internal Flash and so always external access occur regardless the current state of EA.


Peter