0000 RAM in first 32K less final 256 bytes
7exx Terbium workspace RAM
7fxx I/O space:
XBUS_CS0; ADDR $7F00; SIZE 32
XBUS_CS1 ADDR $7F20; SIZE 32
XBUS_CS2 ADDR $7F40; SIZE 32
XBUS_CS3 ADDR $7F60; SIZE 32
USER_ACIA ADDR $7F80; SIZE 4
USER_PIA ADDR $7FA0; SIZE 32
USER_VIA ADDR $7FC0; SIZE 32
SYSTEM_VIA ADDR $7FE0; SIZE 32
8000 Start of 32K Flash ROM, start of Terbium IDE.
853B End of Terbium IDE (in the particular ROM disassembled)
ABORT ADDR $FFF8; SIZE 2
NMI ADDR $FFFA; SIZE 2
RESET ADDR $FFFC; SIZE 2
IRQ ADDR $FFFE; SIZE 2
Like the BBC Micro, it uses the first 32K for RAM and the last 32K for ROM.
The BBC Micro disables three 256-byte pages of ROM space for I/O devices.
The WD65C02SXB disabled one 256-byte page of RAM space for I/O devices.
This decoding is done by U6,10,12,13 which are simple to modify logically but not physically, because they are surface-mount TSSOP. I can do it but would probably need to restore it in future. I would also have to mod the IDE software too.