ADE7518
0xFF
0x80
0x7F
0x00
ACCESSIBLE BY
INDIRECT ADDRESSING
ONLY
ACCESSIBLE BY
DIRECT AND INDIRECT
ADDRESSING
ACCESSIBLE BY
DIRECT ADDRESSING
ONLY
Extended Internal RAM (XRAM)
The ADE7518 provides 256 bytes of extended on-chip RAM,
which is located in Address 0x0000 through Address 0x00FF in
the extended RAM space. No external RAM is supported. To
select the extended RAM memory space, the extended indirect
GENERAL-PURPOSE RAM
SPECIAL FUNCTION REGISTERS (SFRs)
addressing modes are used. The internal XRAM is enabled in
the Configuration SFR (CFG, 0xAF) by writing 01 to CFG[1:0].
Figure 70. General-Purpose RAM and SFR Memory Address Overlap
Both direct and indirect addressing can be used to access general-
0x00FF
256 BYTES OF
EXTENDED INTERNAL
RAM (XRAM)
purpose RAM from 0x00 through 0x7F. However, only indirect
addressing can be used to access general-purpose RAM from
0x80 through 0xFF because this address space shares the same
space with the special function registers (SFRs).
The 8052 core also has the means to access individual bits of
certain addresses in the general-purpose RAM and special
function memory spaces. The individual bits of general-purpose
RAM Address 0x20 to RAM Address 0x2F can be accessed
through Bit Address 0x00 through Bit Address 0x7F. The
benefit of bit addressing is that the individual bits can be
accessed quickly without the need for bit masking, which takes
more code memory and execution time. The bit addresses for
general-purpose RAM Address 0x20 through RAM Address
0x2F can be seen in Figure 71.
0x0000
Figure 72. Extended Internal RAM (XRAM) Space
Code Memory
Code and data memory are stored in the 16 kB flash memory
space. No external code memory is supported. To access code
memory, code indirect addressing is used.
ADDRESSING MODES
The 8052 core provides several addressing modes. The address-
ing mode determines how the core interprets the memory location
or data value specified in assembly language code. There are six
addressing modes, as shown in Table 53.
Table 53. 8052 Addressing Modes
BYTE
ADDRESS
BIT ADDRESSES (HEXA)
Addressing Mode
Example
Bytes
Core Clock
Cycles
0x2F
0x2E
0x2D
0x2C
0x2B
0x2A
0x29
0x28
0x27
0x26
0x25
0x24
0x23
0x22
7F
77
6F
67
5F
57
4F
47
3F
37
2F
27
1F
17
7E
76
6E
66
5E
56
4E
46
3E
36
2E
26
1E
16
7D
75
6D
65
5D
55
4D
45
3D
35
2D
25
1D
15
7C
74
6C
64
5C
54
4C
44
3C
34
2C
24
1C
14
7B
73
6B
63
5B
53
4B
43
3B
33
2B
23
1B
13
7A
72
6A
62
5A
52
4A
42
3A
32
2A
22
1A
12
79
71
69
61
59
51
49
41
39
31
29
21
19
11
78
70
68
60
58
50
48
40
38
30
28
20
18
10
Immediate
Direct
Indirect
Extended Direct
Extended Indirect
Code Indirect
MOV A, #A8h
MOV DPTR, #A8h
MOV A, A8h
MOV A, IE
MOV A, R0
MOV A, @R0
MOVX A, @DPTR
MOVX A, @R0
MOVC A, @A+DPTR
MOVC A, @A+PC
JMP @A+DPTR
2
3
2
2
1
1
1
1
1
1
1
2
3
2
2
1
2
4
4
4
4
3
0x21
0x20
0F
07
0E
06
0D
05
0C
04
0B
03
0A
02
09
01
08
00
Immediate Addressing
Figure 71. Bit Addressable Area of General-Purpose RAM
Bit addressing can be used for instructions that involve Boolean
variable manipulation and program branching (see the Instruction
Set section).
Special Function Registers
Special function registers are registers that affect the function of
the 8052 core or its peripherals. These registers are located in
RAM in Address 0x80 through Address 0xFF. They are only
In immediate addressing, the expression entered after the
number sign (#) is evaluated by the assembler and stored in the
specified memory address. This number is referred to as a literal
because it refers only to a value and not to a memory location.
Instructions using this addressing mode are slower than those
between two registers because the literal must be stored and
fetched from memory. The expression can be entered as a
symbolic variable or an arithmetic expression; the value is
computed by the assembler.
accessible through direct addressing, as shown in Figure 70.
The individual bits of some SFRs can be accessed for use in
Boolean and program branching instructions. These SFRs are
labeled as bit-addressable and the bit addresses are given in the
SFR Mapping section.
Rev. 0 | Page 67 of 128
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