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SH79F3283
23
7.2 RAM
7.2.1 Features
SH79F3283 provides both internal RAM and external RAM for random data storage. The internal data memory is mapped into
four separated segments:
The Lower 128 bytes of RAM (addresses 00H to 7FH) are directly and indirectly addressable.
The Upper 128 bytes of RAM (addresses 80H to FFH) are indirectly addressable only.
The Special Function Registers (SFR, addresses 80H to FFH) are directly addressable only.
The 1280 bytes of external RAM (addresses 00H to FFH) are indirectly accessed by MOVX instructions.
The Upper 128 bytes occupy the same address space as SFR, but they are physically separate from SFR space. When an
instruction accesses an internal location above address 7FH, the CPU can distinguish whether to access the upper 128 bytes
data RAM or to access SFR by different addressing mode of the instruction.
SH79F3283 provides an extra 1280 bytes of RAM to support high-level language in external data space. Also, SH79F3283
provides 28 bytes LCD RAM (500H - 51BH).
51BH
7FH
80H
0FFH
0FFH
80H
00H
00H
Upper
128 bytes
Internal
Ram
indirect accesses
Lower
128 bytes
Internal
Ram
direct or indirect
accesses
Extenal
RAM
SFR
Bank0
direct accesses
500H
4FFH
LCD RAM
SFR
Bank1
direct accesses
80H
0FFH
The Internal and External RAM Configuration
The SH79F3283 provides traditional method for accessing of external RAM. Use
MOVXA, @Ri
or
MOVX @Ri, A;
to access
external low 256 bytes RAM;
MOVX A, @DPTR
or
MOVX @DPTR, A
also to access external 1308 bytes RAM.
In SH79F3283 the user can also use XPAGE register to access external RAM only with
MOVX A, @Ri
or
MOVX @Ri, A
instructions. The user can use XPAGE to represent the high byte address of RAM above 256 Bytes.
In Flash SSP mode, the XPAGE can also be used as sector selector (Refer to SSP Function).
7.2.2 Register
Table 7.3
Data Memory Page Register
F7H
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
Bit0
XPAGE
-
XPAGE.6
XPAGE.5
XPAGE.4
XPAGE.3
XPAGE.2
XPAGE.1
XPAGE.0
R/W
-
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Reset Value
(POR/WDT/LVR/PIN)
-
0
0
0
0
0
0
0
Bit Number
Bit Mnemonic
Description
6-0
XPAGE[6:0]
RAM Page Selector