Hi Matt,

I have solved your problem for flash MC AT89C52 or such alike. It turned out to be easy. The solution has 3 two-input gates only.

Using it I can have the 64 KB X-data memory and the 64 KB code memory in one chip of 128 KB size. Besides, I can distribute the 128 KB between program and data memory as I wish.

For example, I can get the size of the X-data memory from 0 to 128 KB and the size of the program memory from 8 KB to 128 KB.

By chance (?), I found one more solution. It uses 2 two-input gates but I have no enough time to analyze it to the end.

I can not imagine how to show you the scheme, because I have not the scanner home. Email me if you still interested in this issue: makeev@podolsk.ru

What kind of SRAM do you use?

Regards,
George