Suranaree University Of Technology มทส 2002 Anant Oonsivilai 2002/4/8 Microcomputers and Microprocessors 1 Chapter 5 Addressing Modes

2002/4/82002/4/8 Microcomputers and MicroprocessorsMicrocomputers and Microprocessors 11

Suranaree UniversitySuranaree University

Of TechnologyOf Technologyมทสมทส

2002 Anant Oonsivilai2002 Anant Oonsivilai

Chapter 5Chapter 5Addressing ModesAddressing Modes

222002/4/82002/4/8 Microcomputers and MicroprocessorsMicrocomputers and Microprocessors2002 Anant Oonsivilai2002 Anant Oonsivilai

OutlinesOutlines

Five addressing modes of 8051Five addressing modes of 8051

Code instructions using each addressing Code instructions using each addressing modemode

Access RAM using various addressing modesAccess RAM using various addressing modes

SFR addresses (Special Function Register) SFR addresses (Special Function Register)

Access SFRAccess SFR

Operate stack using direct addressing modeOperate stack using direct addressing mode

Code instructions to operate look-up tableCode instructions to operate look-up table


Five Addressing ModesFive Addressing Modes

ImmediateImmediate

RegisterRegister

DirectDirect

Register indirectRegister indirect

IndexedIndexed


Immediate Addressing ModeImmediate Addressing Mode

MOVMOV A,#25HA,#25H ;load 25H into A;load 25H into A

MOV MOV R4,#62R4,#62 ;load the decimal value 62 into R4;load the decimal value 62 into R4

MOV B,#40HMOV B,#40H ;load 40H into B;load 40H into B

MOVMOV DPTR,#4521HDPTR,#4521H ;DPTR=4521H;DPTR=4521H

MOVMOV DPTR,#2550HDPTR,#2550H

;is the same as:;is the same as:

MOVMOV DPL,#50HDPL,#50H

MOVMOV DPH,#25HDPH,#25H


MOVMOV DPTR,#68975DPTR,#68975 ;illegal!! value > 65535 (FFFFH);illegal!! value > 65535 (FFFFH)

COUNTCOUNT EQU 30 EQU 30

…… … …

MOV MOV R4,#COUNT R4,#COUNT ;R4=1E (30=1EH) ;R4=1E (30=1EH)

MOV DPTR,#MYDATAMOV DPTR,#MYDATA ;DPTR=200H;DPTR=200H

ORGORG 200H 200H

MYDATA:MYDATA: DB “America” DB “America”


Register Addressing ModeRegister Addressing Mode

MOVMOV A,R0A,R0 ;copy the contents of R0 into A;copy the contents of R0 into A

MOVMOV R2,AR2,A ;copy the contents of A into R2;copy the contents of A into R2

ADDADD A,R5A,R5 ;add the contents of R5 to contents of A;add the contents of R5 to contents of A

ADDADD A,R7A,R7 ;add the contents of R7 to contents of A;add the contents of R7 to contents of A

MOVMOV R6,AR6,A ;save accumulator in R6;save accumulator in R6

MOVMOV DPTR,#25F5HDPTR,#25F5H

MOVMOV R7,DPLR7,DPL

MOVMOV R6,DPHR6,DPH


Direct Addressing ModeDirect Addressing Mode

RAM addresses 00 to 7FHRAM addresses 00 to 7FHMOVMOV R0,40HR0,40H ;save content of RAM location 40H in R0;save content of RAM location 40H in R0

MOVMOV 56H,A56H,A ;save content of A in RAM location 56H;save content of A in RAM location 56H

MOVMOV R4,7FHR4,7FH ;move contents of RAM location 7FH to R4;move contents of RAM location 7FH to R4

MOVMOV A,4A,4 ;is same as;is same as

MOV A,R4MOV A,R4 ;which means copy R4 into A;which means copy R4 into A

MOVMOV A,7A,7 ;is same as;is same as

MOVMOV A,R7A,R7 ;which means copy R7 into A;which means copy R7 into A


MOVMOV A,2A,2 ;is the same as;is the same as


MOVMOV A,0A,0 ;is the same as;is the same as


MOVMOV R2,#5R2,#5 ;R2=05;R2=05

MOVMOV A,2A,2 ;copy R2 to A (A=R2=05);copy R2 to A (A=R2=05)

MOVMOV B,2B,2 ;copy R2 to B (B=R2=05);copy R2 to B (B=R2=05)

MOVMOV 7,27,2 ;copy R2 to R7;copy R2 to R7

;since “MOV R7,R2” is invalid;since “MOV R7,R2” is invalid


SFR Registers & Their SFR Registers & Their AddressesAddresses

MOVMOV 0E0H,#55H0E0H,#55H ;is the same as;is the same as

MOVMOV A,#55HA,#55H ;which means load 55H into A (A=55H);which means load 55H into A (A=55H)

MOVMOV 0F0H,#25H0F0H,#25H ;is the same as;is the same as

MOV B,#25HMOV B,#25H ;which means load 25H into B (B=25H);which means load 25H into B (B=25H)

MOVMOV 0E0H,R20E0H,R2 ;is the same as;is the same as


MOVMOV 0F0H,R00F0H,R0 ;is the same as;is the same as

MOVMOV B,R0B,R0 ;which means copy R0 into B;which means copy R0 into B


SFR Addresses ( 1 of 2 )SFR Addresses ( 1 of 2 )


SFR Addresses ( 2 of 2 )SFR Addresses ( 2 of 2 )


ExampleExample


Stack and Direct Addressing ModeStack and Direct Addressing Mode

Only direct addressing is allowed for stackOnly direct addressing is allowed for stack


Register Indirect Addressing ModeRegister Indirect Addressing Mode

Only R0 & R1 can be usedOnly R0 & R1 can be used

MOVMOV A,@R0A,@R0 ;move contents of RAM location whose;move contents of RAM location whose

;address is held by R0 into A;address is held by R0 into A

MOVMOV @R1,B@R1,B ;move contents of B into RAM location;move contents of B into RAM location

;whose address is held by R1;whose address is held by R1


Example ( 1 of 2 )Example ( 1 of 2 )




Advantage of Register Indirect Advantage of Register Indirect AddressingAddressing

Looping not possible in direct addressingLooping not possible in direct addressing


ExampleExample


Index Addressing Mode & On-chip ROM Index Addressing Mode & On-chip ROM AccessAccess

Limitation of register indirect addressing: Limitation of register indirect addressing: 8-bit addresses (internal RAM)8-bit addresses (internal RAM)

DPTR: 16 bitsDPTR: 16 bits

MOVCMOVC A, @A+DPTRA, @A+DPTR ; “C” means ; “C” means program (code) space ROMprogram (code) space ROM












Look-up Table & Indexed Look-up Table & Indexed AddressingAddressing


ExampleExample

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Suranaree University Of Technology มทส 2002 Anant Oonsivilai 2002/4/8 Microcomputers and Microprocessors 1 Chapter 5 Addressing Modes