ADE7166 datasheet(82/144 Pages) AD

82 / 144 page

ADE7566/ADE7569/ADE7166/ADE7169

Rev. A | Page 82 of 144

Address 0x80 through Address 0xFF of general-purpose RAM

are shared with the special function registers. The mode of

addressing determines which memory space is accessed, as

shown in Figure 83.

GENERAL-PURPOSE RAM

SPECIAL FUNCTION REGISTERS (SFRs)

ACCESSIBLE BY

INDIRECT ADDRESSING

ONLY

ACCESSIBLE BY

DIRECT AND INDIRECT

ADDRESSING

ACCESSIBLE BY

DIRECT ADDRESSING

ONLY

0xFF

0x80

0x7F

0x00

Figure 83. General-Purpose RAM and SFR Memory Address Overlap

Both direct and indirect addressing can be used to access general-

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 Address 0x2F can be accessed through

their 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 Address 0x2F can be seen in Figure 84.

BYTE

ADDRESS

BIT ADDRESSES (HEXA)

0x2F

0x2E

0x2D

0x2C

0x2B

0x2A

0x29

0x28

0x27

0x26

0x25

0x24

0x23

0x22

0x21

0x20

Figure 84. 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

accessible through direct addressing as shown in Figure 83.

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.

Extended Internal RAM (XRAM)

The ADE7566/ADE7569/ADE7166/ADE7169 provide 256

bytes of extended on-chip RAM. No external RAM is

supported. This RAM is located in Address 0x0000 through

Address 0x00FF in the extended RAM space. To select the

extended RAM memory space, the extended indirect addressing

modes are used. The internal XRAM is enabled in the

Configuration SFR (CFG, 0xAF) by writing 01 to CFG[1:0].

256 BYTES OF

EXTENDED INTERNAL

RAM (XRAM)

0x00FF

0x0000

Figure 85. 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

addressing 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 63.

Table 63. 8052 Addressing Modes

Core Clock

Cycles

Addressing Mode

Example

Bytes

Immediate

MOV A,#A8h

MOV DPTR,#A8h

Direct

MOV A,A8h

MOV A,IE

MOV A,R0

Indirect

MOV A,@R0

Extended Direct

MOVX A,@DPTR

Extended Indirect

MOVX A,@R0

Code Indirect

MOVC A,@A+DPTR

MOVC A,@A+PC

JMP @A+DPTR

Immediate Addressing

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.

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