8051 Addressing Modes | Addressing modes of 8051 Microcontroller
Addressing Modes :-
The 8051 provides a total of five distinct addressing modes.
They are as follows:-
1) Immediate addressing modes.
2) Register addressing modes.
3) Direct addressing modes.
4) Register indirect - addressing mode.
5) Indexed addressing mode.
Let us study
different modes with selective examples:-
1) Immediate
Addressing mode:-
In This
addressing mode, the source operated is a constant i.e. immediate data. Note
that the immediate data must be preceded by the pound sign"#".
Example:-
MOV A, # 82H ; load 82H into A
MOV R4, # 100 ; load the decimal value
100 in to R4
MOV B, # 40H ; load 40H in to B
MOV P1, # 55H
; load 55H directly to port 1
MOV DPTR , # 4521 H ;
DPTR =4521 H
2) Register - Addressing Mode:-
Register
addressing mode involves the use of registers to hold data to be manipulated.
Example:-
MOV A,RO ;copy the
contents of R0 in to A
MOV R2,A
;copy the contents of A in to R2
ADD A,R5
;Add contents of R5 to A
MOV R7,DPL ;load R7 with
contents of DPL
3) Direct Addressing mode:-
In direct
addressing mode the data is in a RAM Memory location whose addressing is known
and this address is given as a part of the instruction.
Although the
entire 128 bytes of RAM com be addressed Using direct addressing mode
It is most often
used to access RAM locations 30-7FH
Example:-
MOV R0, 40H
; save content of RAM location 40H in Ro
MOV 7FH, A
; save content of A in to RAM location 7FH
MOV A,07H
;same as move A1 R7 is copies data in R7 to A
MOV 03H, 04H
; it copies data in R4 to R3
4) Indirect addressing mode:-
In the register indirect
addressing mode a register is used as a pointer to the data .only register R0
and R1 are used for internal RAM indirect Data transfer.
When they hold the
address of Rom locations they must be preceded by the “@” symbol.
Example :-
MOV ,A, @R0 ;move
contents of Ram location whose address is help
By R0 in to A
MOV @ R1 ,B ;move
contents of B in to RAM location whose Address is
held by R1
5) Indexed addressing mode :-
Indexed addressing mode
is widely used in accessing data elements of look-up table entries located in the program Rom space of the 8051.
Example :-
MOV A, @ A + DPTR
MOV A, @ A+ PC
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