Instruction 86

7/29/2019 Instruction 86

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INSTRUCTION SET [8086]

* Following are the Data Transfer Types:

1. Move contents of a register, or contents of a memory location, or immediate data toregister or memory location.

2. Data transfer between a segment register and a register.

3. PUSH & POP instructions

4. Exchange instructions.

5. Data transfer with I/O ports

General Purpose Instructions:

Instruction/Syntax Explanations/Example

1 MOVMOV [Dest.], [Source] Copy a byte or a wordBoth source and destination should be of same type (byte

or word)

Ex. MOV AX,BX, MOV CL,0F2H,

MOV AX,25H;

MOV WORD PTR 0F2H[BP],34H

MOV DS,BX

2 PUSH

PUSH [source]

Push the contents of register onto stack top

Ex. PUSH SI, PUSH DS,

PUSH AX

3 POP

POP Destination

Pop to a register from stack top

Ex. POP SI, POP DS,POP AX

4 PUSHF Push the contents of FLAG register onto the stack top

5 POPF Pop the stack top to the FLAG register

6 XCHG

XCHG [Dest.], [Source]

Exchange

Interchange the contents of two registers

Ex. ECHG AX,SI, XCHG BX,43h[SI]

7 XLAT OR XLATB

XLAT

Translate

Translate byte from one code to another code

Ex. MOV BX,ASCII_TABLE

XLAT B

This will require data in AL with ASCII from the

lookup table.

Input / Output Instructions:

8 IN

IN Acc., [port add.]

Copy a data from port to accumulator

Ex. IN AL,OAH,IN AX,22H

9 OUT

OUT [port add.], Acc.

Output a byte or word to a port

Ex. OUT 44H,AL,OUT 22H,AX


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Address Object Instructions:

Instruction/Syntax Explanations/Example10 LEA

LEA [Dest.], [Source]

Load effective Address

Loads effective address of a memory location into aregister

Ex. LEA BX,83H[SI],LEA DX,MSG1

11 LDS

LDS [Dest.], [Source]

Load register and DS with words from memory.

(REG) Source

(DS) Source + 2

Ex. LDS SI,[200]

LDS BX,82H[SI]

12 LES

LES [Dest.], [Source]

Load registers and ES with words from memory.

(REG) source

(ES)source + 2

Ex. LES AX, [12345]

LES BX,42H[SI]

13 LAHF

LAHF

Load AH with LS byte of FLAG Register

LS of FLAG register.

(AH)

14 SAHF

SAHF

Store AH contents in the LS byte of FLAG register.

(AH)

Arithmetic Group15 AAA

AAA

ASCII adjust for addition.

Ex. ADD AL, BL; if AL+BL=67H, then

AAA; AL contains 07H

16 DAA

DAA

Decimal adjust AL after BCD addition.

DAA operates only on [AL] register

Ex. ADD AL, BL; 59+34=>8DH

DAA; Adds O6 to AL as lower nibble value is greater

than 9

17 NEG

NEG destination

Negate (Forms 2's complement).

Ex. NEG BX; Replaces word in BX with its 2'scomplement

18 AAS

AAS

ASCII adjust for subtraction.

Ex. SUB AL, DL;

34H-38H=>FCH in AL

AAS;

As lower nibble C is greater than 9 it subtracts

6 from AL and CF is set.

S Z U A U P U C

S Z U A U P U C


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Instruction/Syntax Explanations/Example19 DAS

DAS

Decimal adjust AL after BCD subtraction.

If lower nibble after subtraction is greater than 9, then

subtract 6

from AL (OR if CF is set)Ex. SUB AL, BL;

78H-93H=>E5 with

DAS;

borrow, CF is set

20 AAM

AAM

BCD adjust after multiplication.

Ex. MUL BL;

AL*BL=AX (Say 0020H)

AAM;

AX=0302H

21 CBW

CBW

Convert signed byte to signed word CBW produces a

double length dividend from a byte prior to performing

division.

22 CWD

CWD

Convert signed byte to signed double word.

CWD produces a double length dividend from a word

prior to performing division.

23 AAD

AAD

BCD to binary convert before division.

AAD converts two unpacked BCD digits in AH & AL to

the equivalent binary number

Logical Instructions

24 TEST

TEST [Dest.], [Source]

AND operands to update flags.

TEST instruction performs logical AND of two operands,

updates flag, but does not return result i.e. neither operand

is changed.

Ex. TEST SI, DI

TEST AL, 0100 0100b

25 RCL

RCL [Dest.], [Source]

Rotate operand around to the left through carry.

By default CL register is used.

Ex: RCL AL, CL

26 RCR

RCR [Dest.], [Source]

Rotate operand around to the right through carry.

By default CL register is used.

Ex: RCR AL, CL

Cy MSB

LSB

Cy MSB

LSB


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Instruction/Syntax Explanations/Example27 SHL / SAL

SHL/SAL [Opr], [Cnt]

Shift logical left / shift Arithmetic left.

28 SHR

SHR [Opr], [Cnt]

Shift logical right.

29 SAR

SAR [Opr], [Cnt]

Shift arithmetic right.

Here new MSB = old MSB

Branch Instructions

30 CALL Call procedure

31 RET Return from procedure

32 JMP Jump to specified location

Conditional Transfer Instructions

33 JA / JNBE Jump if above / not below or equal

34 JAE / JNB Jump if above or equal / not below

35 JG / JNLE Jump if greater / not less or equal

36 JLE / JNG Jump if less or equal / not greater

37 JNP / JPO Jump if no parity / odd parity

38 LOOPE / LOOPZ Jump if equal / zero

39 LOOPNE / LOOPNZ Loop if not equal / not zero

40 JCXZJCXZ [location]

Jump if CX is equal to zero.If CX contents are zero, then transfer control to specified

location.

Ex: JCXZ skip_label

* All the BRANCH instructions must have a single operand specifying the location where to

branch. Generally we use LABELS to jump to that particular location depending on the

condition instead of specifying the exact memory location.

Cy MSB LSB

0

CyMSB LSB

0

Cy

MSB

LSB


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Instruction/Syntax Explanations/Example41 INT

INT [Interrupt type]

Interrupt program execution.

Int. type number should be 00H to FFH

Ex: INT 01H, INT 21H

42 IRET Interrupt ReturnIRET transfers control back to the point of interruption

by popping IP, CS & flags from the stack.

Process Control Instructions

43 CLC Clear the Carry flag

44 CMC Complement the Carry flag

45 STC Set the Carry flag

46 CLA Clear Direction flagUsed for string instructions to auto-increment SI & DI

47 STD Set Direction flag

Used for string instructions to auto-decrement SI & DI

48 CLI Clear Interrupt flag

49 STI Set Interrupt flag

50 NOP No Operation

Used for software delays

51 WAIT Wait for test signal at Interrupt signal.

When WAIT is executed 8086 goes into idle condition. It

keeps checking TEST, INTR & NMI52 ESC

ESC [ExtOp],[Source]

Escape

Escape provides a means for an external processor to

obtain an Opcode & possibly a memory operand from

8086

Ex: ESC 6, ARRAY[SI]

ESC 20, AL

53 LOCK Assert bus lock signal.

It is not an instruction but a prefix to be used with

instructions.

Ex: LOCK XCHG FLAG, AL

String Instructions

Register SI & DI must be initialized to point to the source & destination strings before

executing the string instructions.

54 MOVS

MOVS [Dest.],[Source]

OrMOVSB / MOVSW

Move string byte or string word.

Transfers a byte or word from source string to destination

string.

Ex: MOVSB ;Move (DI) (SI)


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Instruction/Syntax Explanations/Example55 CMPS

CMPS [Dest.],[Source]

OrCMPSB / CMPSW

Compare string byte or string word.

It compares byte/word of one string with byte/word of

another string.

Flags affected CF, SF, IF

Ex: CMPS Str1, Str256 SCAS

SCAS [Dest_Str]

OR SCASB,SCASW

Scan a string byte or string word.

SCAS compares byte AL or word in AX with a byte or

word pointed by DI in ES.Destination has to be in

ES.SCAS updates FLAGS but doesnot alter destination

string or accumulator.

EX. SCAS Input_str,

LEA DI,BOFF1

MOV AL,ODH

SCASB

57 LODS

LODS Source_string

OR LODSB,LODSW

Load string byte in AL or load string word in AX.LODS

transfers the byte or word string element addressed by SI

to register AL or AX.

EX. MOV SI,Offset source_str

CLD

LODSB

58 STOS

STOS [Dest_str.]

OR STOSB,STOSW

Store byte or word in string STOS transfers a byte or

word from register AL or AX to the string element

addressed by DI.

EX. MOV DI,Offset atr1

CLD

MOV AX,00HSTOSW

59 LODS

LODS [Src_str.]

OR LODSB,LODSW

Load string byte in AL or load string word in AX.LODS

transfers the byte or word string element addressed by SI

to register AL or AX.

EX.MOV SI,Offset source_str

CLD

LODSB

60 STOS

STOS [Dest_str.]

OR STOSB,STOSW

Store byte or word in string STOS transfers a byte or

word from register AL or AX to the string element

addressed by DI.

EX. MOV DI,Offset atr1CLD

MOV AX,00H

STOSW

61 REP

REP

Repeat string instruction until specified condition exists.

EX. LEA SI,Service_str

LEA DI,Dest_str

MOV CX,20H

CLD

REP MOVSW


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Instruction/Syntax Explanations/Example62 REPE / REPZ Repeat while equal/Repeat while not zero.

This will cause string instructions to be repeated as long

as ZF = 0 & CX != 0.

EX. LEA DI,Str1MOV AL,ODH

CLD

MOV CX,25H

REPE SCASB

63 REPNE / REPNZ Repeat while not equal/Repeat while not zero.

This will cause string instructions to be repeated as long

as ZF = 0 & CX != 0

EX. MOV DI,Offset Str1

MOV CX,100H

CLD

RPNE SCASW

By Asawari D

Dept. of Electronics VESIT ,Mumbai

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Instruction 86