1. MEMORY ORGANIZATION
OF
8051
SMM
NOTES

2. INTERNAL MEMORYINTERNAL MEMORY
A functioning computer must have memory for
program code bytes, commonly in ROM, and
RAM memory for variable data that can be
altered as the program runs
8051 has internal RAM (128 bytes) and ROM
(4Kbytes)
8051 uses the same address but in different
memories for code and data
Internal circuitry access the correct memory
based on the nature of the operation in progress
Can add memory externally if needed

3. 8051 Internal RAM Organisation8051 Internal RAM Organisation
R7
R6
R5
R4
R3
R2
R1
R0
R7
R6
R5
R4
R3
R2
R1
R0
R7
R6
R5
R4
R3
R2
R1
R0
R7
R6
R5
R4
R3
R2
R1
R0
07
06
05
04
03
02
01
00
0F
0E
0D
0C
0B
0A
09
08
17
16
15
14
13
12
11
10
1F
1E
1D
1C
1B
1A
19
18
Bank0Bank1Bank2Bank3
27
26
25
24
23
22
21
20
2F
2E
2D
2C
2B
2A
29
28
7F 78
77 70
6F 68
67 60
5F 58
57 50
4F 48
47 40
3F 38
37 30
2F 28
27 20
1F 18
17 10
0F 08
07 00 30
7F
Working Registers Bit Addressable General Purpose

4. Program Status Word (PSW)Program Status Word (PSW)
Bank Select Bits, RS1, & RS0 to select 1 of 4 register bankBank Select Bits, RS1, & RS0 to select 1 of 4 register bank

5. Internal ROMInternal ROM
Internal ROM occupies the code address space
from 0000H to 0FFFH (Size = 4K byte)
Program addresses higher than 0FFFH will
automatically fetch code bytes from external
program memory
Code bytes can also be fetched exclusively from
an external memory by connecting the external
access pin (EA) to ground

6. Interfacing with External Program MemoryInterfacing with External Program Memory

7. Interfacing with External Data MemoryInterfacing with External Data Memory

8.  Read referenceRead reference
The 8051 Microcontroller and
Embedded Systems - Using Assembly
and C, Mazidi
• The 8051 Microcontroller – Hardware,
Software and Interfacing, James W.
Stewart
• Microprocessor and Micro controllers –
Prof. C.R.Sharma, Premier publishing
house