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Suranaree University
Of Technology
มทส
Chapter 5
Addressing Modes
2002/4/8
2002 Anant Oonsivilai
Microcomputers and Microprocessors
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Outlines
Five addressing modes of 8051
Code instructions using each addressing
mode
Access RAM using various addressing modes
SFR addresses (Special Function Register)
Access SFR
Operate stack using direct addressing mode
Code instructions to operate look-up table
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Five Addressing Modes
Immediate
Register
Direct
Register indirect
Indexed
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Immediate Addressing Mode
MOV
MOV
MOV
MOV
A,#25H
R4,#62
B,#40H
DPTR,#4521H
MOV
DPTR,#2550H
;is the same as:
DPL,#50H
DPH,#25H
MOV
MOV
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;load 25H into A
;load the decimal value 62 into R4
;load 40H into B
;DPTR=4521H
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MOV
DPTR,#68975 ;illegal!! value > 65535 (FFFFH)
COUNT
…
MOV
MOV
ORG
MYDATA:
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EQU 30
…
R4,#COUNT
DPTR,#MYDATA
;R4=1E (30=1EH)
;DPTR=200H
200H
DB “America”
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Register Addressing Mode
MOV
MOV
ADD
ADD
MOV
A,R0
R2,A
A,R5
A,R7
R6,A
MOV
MOV
MOV
DPTR,#25F5H
R7,DPL
R6,DPH
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;copy the contents of R0 into A
;copy the contents of A into R2
;add the contents of R5 to contents of A
;add the contents of R7 to contents of A
;save accumulator in R6
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Direct Addressing Mode
RAM addresses 00 to 7FH
MOV
MOV
MOV
R0,40H
56H,A
R4,7FH
;save content of RAM location 40H in R0
;save content of A in RAM location 56H
;move contents of RAM location 7FH to R4
MOV
MOV
A,4
A,R4
;is same as
;which means copy R4 into A
MOV
MOV
A,7
A,R7
;is same as
;which means copy R7 into A
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MOV
MOV
A,2
A,R2
;is the same as
;which means copy R2 into A
MOV
MOV
A,0
A,R0
;is the same as
;which means copy R0 into A
MOV
MOV
MOV
MOV
R2,#5
A,2
B,2
7,2
;R2=05
;copy R2 to A (A=R2=05)
;copy R2 to B (B=R2=05)
;copy R2 to R7
;since “MOV R7,R2” is invalid
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SFR Registers & Their
Addresses
MOV
MOV
0E0H,#55H
A,#55H
;is the same as
;which means load 55H into A (A=55H)
MOV
MOV
0F0H,#25H
B,#25H
;is the same as
;which means load 25H into B (B=25H)
MOV
MOV
0E0H,R2
A,R2
;is the same as
;which means copy R2 into A
MOV
MOV
0F0H,R0
B,R0
;is the same as
;which means copy R0 into B
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SFR Addresses ( 1 of 2 )
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SFR Addresses ( 2 of 2 )
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Example
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Stack and Direct Addressing Mode
Only direct addressing is allowed for stack
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Register Indirect Addressing Mode
Only R0 & R1 can be used
MOV
A,@R0
MOV
@R1,B
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;move contents of RAM location whose
;address is held by R0 into A
;move contents of B into RAM location
;whose address is held by R1
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Example ( 1 of 2 )
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Example ( 2 of 2 )
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Advantage of Register Indirect
Addressing
Looping not possible in direct addressing
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Example
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Index Addressing Mode & On-chip ROM
Access
Limitation of register indirect addressing:
8-bit addresses (internal RAM)
DPTR: 16 bits
MOVC A, @A+DPTR ; “C” means
program (code) space ROM
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Example ( 1 of 2 )
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Example ( 2 of 2 )
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Example ( 1 of 3 )
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Example ( 2 of 3 )
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Example ( 3 of 3 )
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Look-up Table & Indexed
Addressing
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Example
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