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CHAPTER 3 CPU ARCHITECTURE
User’s Manual U12697EJ3V0UM
(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, see
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 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 in this text are the addresses when the LOCATION 0H instruction is executed. When
the LOCATION 0FH instruction is executed, 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.
