VRS51x540
______________________________________________________________________________________________
www.ramtron.com
page 7 of 40
Program Memory Structure
Program Memory
The VRS51x540 includes 4k of on-chip Program Flash
memory.
FIGURE 3: VRS51X540 INTERNAL PROGRAM MEMORY
VRS51x540
Flash Memory
(4K Bytes)
0000h
FFFh
Program Status Word Register
The PSW register is a bit addressable register that
contains the status flags (CY, AC, OV, P), user flag
(F0) and register bank select bits (RS1, RS0) of the
8051 processor.
TABLE 7: PROGRAM STATUS WORD REGISTER (PSW) - SFR DOH
7
6
5
4
3
2
1
0
CY
AC
F0
RS1
RS0
OV
-
P
Bit
Mnemonic
Description
7
CY
Carry Bit
6
AC
Auxiliary Carry Bit from bit 3 to 4.
5
F0
User flag
4
RS1
R0-R7 Registers bank select bit 0
3
RS0
R0-R7 Registers bank select bit 1
2
OV
Overflow flag
1
-
-
0
P
Parity flag
RS1
RS0
Active Bank
Address
0
0
0
00h-07h
0
1
1
08h-0Fh
1
0
2
10h-17h
1
1
3
18-1Fh
Data Pointer
The VRS51x540 has one 16-bit data pointer. The
DPTR is accessed through two SFR addresses: DPL
located at address 82h and DPH located at address
83h.
Data Memory
The VRS51x540 has a total of 128 Bytes of RAM
memory configured as the internal memory structure of
a standard 8051.
FIGURE 4: VRS51X540 DATA MEMORY
128 bytes RAM
(Can be accessed in indirect and
direct addressing mode)
SFR
(Direct addressing mode only)
128 bytes RAM
(indirect addressing only)
80h
FFh
7Fh
00h
Lower 128 bytes (00h to 7Fh, Bank 0 & Bank 1)
The lower 128 bytes of data memory (from 00h to 7Fh)
is summarized as follows:
• Address range 00h to 7Fh can be accessed in
direct and indirect addressing modes.
• Address range 00h to 1Fh includes R0-R7
registers area.
• Address range 20h to 2Fh is bit addressable.
• Address range 30h to 7Fh is not bit addressable
and can be used as general-purpose storage.
.
FIGURE 5: VRS51X540 INTERNAL RAM STRUCTURE
Registers Bank 0
R7
-
R0
Registers Bank 1
R7
-
R0
Registers Bank 2
R7
-
R0
Registers Bank 3
R7
-
R0
80 Bytes of
General Purpose RAM
00h
08h
10h
18h
20h
07
06
05
04
03
02
01
00
0F
0E
0D
0C
0B
0A
09
08
77
76
75
74
73
72
71
70
7F
7E
7D
7C
7B
7A
79
78
30h
SFR Area
Direct or Bit Access Only
80h
7Fh
2Fh
FFh
85
84
83
82
81
80
P0
SP
DPL
DPH
87
86
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
