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CHAPTER 3 CPU ARCHITECTURE
User
’
s Manual U15017EJ2V0UD
(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 that are 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, refer to
78K/IV Series User
’
s Manual Instruction (U10905E)
.
A program cannot be fetched from IRAM. If a program is fetched from an address that is mapped by IRAM, the
CPU runs wild.
The following areas are reserved in IRAM.
General-purpose register area:
Macro service control word area: FE06H to FE2BH
Macro service channel area:
FE80H to FEFFH
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 in this text are the addresses when the LOCATION 0H instruction is executing. When
the LOCATION 0FH instruction is executing, 0F0000H is added to the values in this text.
(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 register (SFR) of the on-chip peripheral hardware is mapped to the area from 0FF00H to
0FFFFH (refer to
Figures 3-2
and
3-3
).
Caution In this area, do not access an address that is not mapped in SFR. If mistakenly accessed, the
CPU enters the deadlock state. The deadlock state is released only by reset input.
Remark
The addresses in this text are the addresses only when the LOCATION 0H instruction is executing. If
the LOCATION 0FH instruction is executing, 0F0000H is added to the values in the text.