4 data memory addressing – NEC switch User Manual

Page 38

CHAPTER 3 CPU ARCHITECTURE

User’s Manual U12978EJ3V0UD

3.1.4 Data memory addressing

The

µPD789800 Subseries provides a variety of addressing modes which take account of memory manipulability,

etc. Especially at addresses corresponding to data memory area (FE00H to FFFFH), particular addressing modes

are possible to meet the functions of the special function registers (SFR) and general-purpose registers. Figures 3-3

and 3-4 show the data memory addressing modes.

Figure 3-3. Data Memory Addressing (

µµµµPD789800)

Special function registers (SFR)

256

× 8 bits

Internal high-speed RAM

256

× 8 bits

Internal ROM
8,192

× 8 bits

FFFFH

0000H

Direct addressing

Based addressing

FF00H

FEFFH

FF20H

FF1FH

FE20H

FE1FH

SFR addressing

Short direct
addressing

Reserved

FE00H

FDFFH

2000H

1FFFH