University of Thi-Qar
College of Engineering
Department of Electrical and Electronic Engineering
MICROPROCESSOR
Lecture3
BY
MSc. Zahraa M. Baqir
Addressing Modes in 8086
Examples of the register-addressed instructions.
Examples of the immediate-addressed instructions.
Assembly Language
MOV BL,44
MOV AX,44H
MOV SI,0
MOV CH,100
MOV AL,’A’
MOV AX,’AB’
MOVCL,11001110B
size
8-bits
16-bits
16-bits
8-bits
8-bits
16-bits
8-bits
Operation
Copies a 44 decimal into BL
Copies a 0044H into AX
Copies a 0000H into SI
Copies a 100 decimal into CH
Copies an ASCII A into AL
Copies an ASCII BA into AX
Copies a 11001110 binary into CL
Examples: Direct Addressing Modes
MOV DL, [2400]
;move contents of DS:2400 intoDL
MOV CX, [3200]
; move contents of DS:3200 into CX
Examples: Register indirect addressing modes
MOV AL, [BX]
;move contents of DS:BX into AL
MOV CL, [SI]
MOV [DI], AH
; move contents of DS:SI into CL
; move contents of AH into DS:DI
Examples: indexed relative addressing mode
MOV DX,[SI]+5;PA=DS*10+SI+5
MOV CL,[DI]+20;PA=DS*10+DI+20
Examples:based indexed addressing mode
Ex1:
MOV AL, [2000 H]
; PA=DS*10 + 2000 H
Ex2:
MOV AX, [SI]
;PA=DS*10 + (SI)
PA=02000 + 1234 = 03234 H
Ex3:
MOV [BX]+1234 H, AL .
If (AL)=ED H,
(DS)=0200H
and (BX)=1000 H.
PA=(DS)*10 + (BX) + 1234 H
PA= 0200 H*10 + 1000 H+ 1234 H
PA=02000 + 1000 + 1234
PA=04234 H
;copy of (AL)=ED H
Ex4:
MOV CX, [BX]
;PA= DS*10 + (BX).
MOV [Bp], BL
;PA= SS*10 + (Bp).
MOV [DI], AH
;PA= DS*10 + (DI).
MOV [DI], [BX]
;NOT ALLOWED.
❖ Data Transfer Group:
1-The MOV Instruction:
Mnemonic
Meaning
Format
Operation
Flags affected
MOV
move
MOV D,S
(S)→(D)
None
2-PUSH/POP Instructions:
Mnem.
Meaning
Format
Operation
Flags
PUSH
Push word
onto stack
PUSH S
None
POP
POP word
onto stack
POP D
(Sp-1) ← (S)
(Sp) ← (Sp)2
(D) ← (Sp)
(Sp) ←
(Sp)+2
None
Operand (S
or D)
Register
Seg reg (CS
illegal)
Memory
Flag register
Example:
MOV AX, 6000H
MOV SS, AX
MOV SP, 7500H
MOV BX, 5378H
PUSH BX
POP BX
(PA=SS*10+SP-1)=(BH)
(60000+7500-1)= (BH)
(674FF)= 53 H
(60000+7500-2)= (BL)
(674FE)= 78 H
(SP) = 7500-2
(SP) = 74FE H
(BL) = (PA=SS*10+SP)
(BL) = (60000+74FE)= 78 H
(BH) = (60000+SP+1)
(BH) = (674FF)= 53 H
(SP) = 7500 H
3- XCHG Instruction:
4- XLAT Instruction :
Example:
XCHG AL, BL
XCHG [BX][DI], CX
XCHG AX, SP
Example:
MOV AX, 2200 H
MOV DS, AX
MOV AL, 15 H
MOV BX, 1234 H
XLAT
HLT
;
;
Homework
Q1/ What is the result of executing the following instruction sequence?
MOV AX, EDH
MOV SS, AX
MOV SP, 7500H
MOV BX, 1000H
PUSH BX
POP BX
Q2/ What is the result of executing the following instruction sequence ?
MOV AX, 0A
MOV BX, 100
MOV CX,3579
MOV DS, 2200
XCHG AL, BL
MOV CL, BL
XCHG [BX][DI], CX
XLAT
HLT
Q3/ Fill blanks
1. MOV SI,DI is example of --------------------addressing mode.
2. MOV AL,’G’ is an example of --------------------addressing mode.
3. MOV AL, [BX] is an example of --------------------addressing mode.
4. MOV CL,[DI]+20 is an example of --------------------addressing mode.
5. MOV CL,[BX][DI]+6 is an example of --------------------addressing mode.
6. Physical address is -------------------If (AL)=ED H, (DS)=200H and (BX)=1000 H.