Hello Stephane,

use an external EPROM (32K at adr. 0x0000) for the bootloader, an external SRAM (32K at adr. 0x0000) for data storage and an external SRAM / Flash (32K banks at adress 0x8000) for the code.

If your bootloader doesn't need to be changed anymore, you can program it to the internal EPROM of the 87C591 and use an external SRAM for both the code and the data storage (/PSEN and /RD connected together via an AND, /PSEN is a push-pull output!).

There are not too much pins left for usage...

Mike