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CHAPTER 2 MEMORY SPACE
2.4.2 Special function register (SFR) area
The on-chip peripheral hardware special function registers (SFRs) are mapped onto the area from 0FF00H to
0FFFFH (see the
User’s Manual — Hardware
for the individual products).
In some products, the area from 0FFD0H to 0FFDFH is mapped as an external SFR area, and allows externally
connected peripheral I/Os, etc., to be accessed in external memory extension mode (specified by the memory
extension mode register (MM)) by ROM-less products or on-chip ROM products.
Caution
Addresses onto which SFRs are not mapped should not be accessed in this area. If such an address
is accessed by mistake, the CPU may become deadlocked. A deadlock can only be released by reset
input.
Remark
The addresses in this text are those that apply when the LOCATION 0 instruction is executed. When
the LOCATION 0FH instruction is executed, 0F0000H should be added to the values shown.
The
μ
PD784915 Subseries is fixed to the LOCATION 0 instruction.
2.4.3 External SFR area
In some 78K/IV Series products, the 16-byte area from 0FFD0H to 0FFDFH in the SFR area (when the LOCATION
0 instruction is executed; 0FFFD0H to 0FFFDFH when the LOCATION 0FH instruction is executed) is mapped as
an external SFR area. When the external memory extension mode is set in a ROM-less product or on-chip ROM
product, externally connected peripheral I/Os, etc., can be accessed using the address bus or address/data bus, etc.
As the external SFR area can be accessed by SFR addressing, peripheral I/O and similar operations can be
performed easily, the object size can be reduced, and macro service can be used.
Bus operations for accesses to the external SFR area are performed in the same way as for ordinary memory
accesses.
2.5 External Memory Space
The external memory space is a memory space that can be accessed in accordance with the setting of the memory
extension mode register (MM). It can hold programs, table data, etc., and can have peripheral I/O devices allocated
to it.
A program cannot be allocated to the area from 100000H to 0FFFFFFH in the external memory space.
Note also that some products do not have an external memory space.