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CHAPTER 3
CPU ARCHITECTURE
User’s Manual U12790EJ2V0UD
3.1.2 Internal data memory space
The
PD178078 and 178098A Subseries products incorporate the following RAMs.
(1) Internal high-speed RAM
A high-speed memory of 1024 bytes is incorporated.
In this area, four banks of general-purpose registers, each bank consisting of eight 8-bit registers, are allocated
in the 32-byte area FEE0H to FEFFH.
This area cannot be used as a program area to which instructions are written and executed.
The internal high-speed RAM can also be used as a stack memory area.
(2) Buffer RAM
Buffer RAM is allocated to the 32-byte area from FAC0H to FADFH. Buffer RAM is used to store transmit/
receive data for serial interface channel 1 (3-wire serial I/O mode with automatic transmit/receive function).
When not used in this mode, buffer RAM can also be used as normal RAM.
(3) Internal expansion RAM
Internal expansion RAM is allocated to the 1024-byte area from F400H to F7FFH in the
PD178076 and
178096A. For the
PD178078, 178098A, and 178F098, it is allocated to the 2048-byte area from F000H to
F7FFH.
This area can be used as a normal data area like the internal high-speed RAM, and also as a program area
to which instructions are written and executed.
The internal expansion RAM cannot be used as a stack memory.
3.1.3 Special-function register (SFR) area
On-chip peripheral hardware special-function registers (SFRs) are allocated in the area FF00H to FFFFH. (Refer
to Table 3-4 Special-Function Registers.)
Caution Do not access addresses where an SFR is not assigned.