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Preliminary Technical Data

ADE5166/ADE5169/ADE5566/ADE5569

Rev. PrB | Page 79 of 148

Table 66. 8052 Addressing Modes

Addressing Mode

Example

Bytes

Core Clock

Cycles

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

memory address specified. 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 is 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.

Direct Addressing

With direct addressing, the value at the source address is moved

to the destination address. Direct addressing provides the fastest

execution time of all the addressing modes when an instruction

is performed between registers using direct addressing. Note

that indirect or direct addressing modes can be used to access

general-purpose RAM Address 0x00 through Address 0x7F. An

instruction with direct addressing that uses an address between

0x80 and 0xFF is referring to a special function memory location.

Indirect Addressing

With indirect addressing, the value pointed to by the register is

moved to the destination address. For example, to move the

contents of internal RAM Address 0x82 to the accumulator, use

the following two instructions, which require a total of four

clock cycles and three bytes of storage in the program memory:

MOV

R0,#82h

MOV

A,@R0

Indirect addressing allows addresses to be computed, and is

useful for indexing into data arrays stored in RAM.

Note that an instruction that refers to Addresses 0x00 through

Address 0x7F is referring to internal RAM, and indirect or direct

addressing modes can be used. An instruction with indirect

addressing that uses an address between 0x80 and 0xFF is

referring to internal RAM, not to an SFR.

Extended Direct Addressing

The DPTR register is used to access internal extended RAM in

extended indirect addressing mode. The ADE5166/ADE5169/

ADE5566/ADE5569 provide 2 kB of internal extended RAM

(XRAM), accessed through MOVX instructions. External

memory spaces are not supported on the ADE5166/ADE5169/

ADE5566/ADE5569.

In extended direct addressing mode, the DPTR register points

to the address of the byte of extended RAM. The following code

moves the contents of extended RAM Address 0x100 to the

accumulator:

MOV

DPTR,#100h

MOVX

A,@DPTR

These two instructions require a total of seven clock cycles and

four bytes of storage in the program memory.

Extended Indirect Addressing

The internal extended RAM is accessed through a pointer to the

address in indirect addressing mode. The ADE5166/ADE5169/

ADE5566/ADE5569 provide 2 kB of internal extended RAM,

accessed through MOVX instructions. External memory is not

supported on the ADE5166/ADE5169/ADE5566/ADE5569.

In extended indirect addressing mode, a register holds the

address of the byte of extended RAM. The following code

moves the contents of extended RAM Address 0x80 to the

accumulator:

MOV

R0,#80h

MOVX A,@R0

These two instructions require six clock cycles and three bytes

of storage.

Note that there are 2 kB of extended RAM, so both extended

direct and extended indirect addressing can cover the whole

address range. There is a storage and speed advantage to using

extended indirect addressing because the additional byte of

addressing available through the DPTR register that is not

needed is not stored.

From the three examples demonstrating the access of internal

RAM from 0x80 through 0xFF and extended internal RAM

from 0x00 through 0xFF, it can be seen that it is most efficient

to use the entire internal RAM accessible through indirect

access before moving to extended RAM.

Code Indirect Addressing

The internal code memory can be accessed indirectly. This can

be useful for implementing lookup tables and other arrays of

constants that are stored in Flash. For example, to move the data

stored in Flash memory at Address 0x8002 into the accumulator:

MOV

DPTR,#8002h

CLR

MOVX

A,@A+DPTR

The accumulator can be used as a variable index into the array

of flash memory located at DPTR.

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