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CHAPTER 3
CPU ARCHITECTURE
User’s Manual U12697EJ4V1UD
(1) Internal high-speed RAM (IRAM)
The internal high-speed RAM can be accessed at high speed. FD20H to FEFFH can use the short direct
addressing mode for high-speed access. The two short direct addressing modes are short direct addressing 1
and short direct addressing 2, based on the address of the target. Both addressing modes have the same function.
In a portion of the instructions, short direct addressing 2 has a shorter word length than short direct addressing
1. For details, see 78K/IV Series Instruction User’s Manual (U10905E).
A program cannot be fetched from IRAM. If a program is fetched from an address that is mapped by IRAM, the
CPU inadvertently loops.
The following areas are reserved in IRAM.
General-purpose register area:
FE80H to FEFFH
Macro service control word area: FE06H to FE39H
Macro service channel area:
FE00H to FEFFH (the address is set by a macro service control word)
When reserved functions are not used in these areas, they can be used as normal data memory.
Remark
The addresses here are the addresses when the LOCATION 0H instruction is executed. When the
LOCATION 0FH instruction is executed, 0F0000H is added to the values here.
(2) Peripheral RAM (PRAM)
The peripheral RAM (PRAM) is used as normal program memory or data memory. When used as the program
memory, the program must be written beforehand in the peripheral RAM by a program.
A program fetch from the peripheral RAM is high speed and can occur in two clocks in 2-byte units.
3.4.2 Special function register (SFR) area
The special function registers (SFRs) of the on-chip peripheral hardware are mapped to the area from 0FF00H
to 0FFFFH (refer to Figures 3-1 and 3-2).
The area from 0FFD0H to 0FFDFH is mapped as the external SFR area. Peripheral I/O externally connected in
the external memory expansion mode (set by the memory expansion mode register (MM)) can be accessed.
Caution In this area, do not access an address that is not mapped in the SFR area. If mistakenly accessed,
the CPU enters the deadlock state. The deadlock state is released only by reset input.
Remark
The addresses here are the addresses only when the LOCATION 0H instruction is executed. If the
LOCATION 0FH instruction is executed, 0F0000H is added to the values here.
3.4.3 External SFR area
In the products of the
PD784225 Subseries, the 16-byte area of the 0FFD0H to 0FFDFH area (during LOCATION
0H instruction execution, or 0FFFD0H to 0FFFDFH area during LOCATION 0FH instruction execution) in the SFR
area is mapped as the external SFR area. In the external memory expansion mode, the address bus and address/
data bus are used and the externally attached peripheral I/O can be accessed.
Since the external SFR area can be accessed by SFR addressing, the features are that peripheral I/O operations
can be simplified; the object size can be reduced; and macro service can be used.
The bus operation when accessing an external SFR area is the same as a normal memory access.
3.5 External Memory Space
The external memory space is the memory space that can be accessed based on the setting of the memory
expansion mode register (MM). The program and table data can be stored and peripheral I/O devices can be assigned.