This way you cannot use NVRAM. It's because PSEN is inactive when you address Data memory (CS is then inactive !), as well as /RD is inactive while fetching the opcode.

The solution is: PSEN-AND-/RD (HC08) to /OE of RAM and /CS of RAM can be grounded (or tied to some other logic if you address more units).

By the way, it's a risk to have common area for program and data, because it can be difficult to trace and find a bug when the code is destroyed.


Regards, Slobodan