8088 Instruction Set Summary Revised August 20, 1997

8088 Instruction Set Summary Revised August 21,2000

This summary has been compiled from a number of sources, but chiefly from 8086/8088/80286 Assembly Language, by Scanlon, and A86 Macro Assembler and D86 Debugger Reference Manual, by Isaacson.

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Instructions Important to El E 485/486

Flags

ADC

Add with carry: dest ¬ dest + source + CF

ADD

Add: dest ¬ dest + source

AND

And: dest ¬ dest .AND. source

CALL

CS:IP or IP ¬ address of procedure,

stack ¬ IP or CS:IP of next instruction

CBW

Convert byte to word. AH ¬ bit 7of AL

CLC

Clear the carry flag. CF ¬ 0

CLI

Clear the interrupt enable bit.

Maskable interrupts are ignored.

CMC

Complement the carry flag

CMP

dest - source, result not stored

CWD

DX ¬ AX15

DEC

Decrement. dest ¬ dest - 1

DIV

Unsigned divide (immediate operand not allowed)

AX ¬ quo of {DX:AX/(word op)} and

DX ¬ rem of {DX:AX/(word op)}

AL ¬ quo of {AX/(byte op)} and

AH ¬ rem of {AX/(byte op)}

IDIV

Signed divide (immediate operand not allowed)

AX, DX ¬ quo, rem of {DX:AX/(word op)}, or

AL, AH ¬ quo, rem of {AX/(byte op)}

IMUL

Signed multiply (immediate operand not allowed)

DX:AX ¬ AX * (word op), or AX ¬ AL * (byte op)

AL ¬ port, or AX ¬ port

port is an immediate 8-bit address or DX

INC

dest ¬ dest + 1

INT

execute a software interrupt

IRET

return from interrupt

Jxx

conditional jumps to a relative address (-128 to +127)

JA/JNBE, JAE/JNB, JB/JNAE, JC, JBE/JNA, JCXZ, JE/JZ, JG/JNLE, JGE/JNL, JL/JNGE, JLE/JNG, JNC, JNE/JNZ, JNO, JNP/JPO, JNS, JO, JP/JPE, JS

JMP

Jump, IP or CS:IP ¬ operand

LEA

dest ¬ address of operand

	Instructions Important to El E 485/486	Flags
		S	Z	C	O	P	A
LOOP	CX ¬ CX - 1, then transfer to short label destination if CX ¹ 0; LOOPE/LOOPZ, transfers if CX ¹ 0 *and* ZF = 1; LOOPNE/LOOPNZ transfers if CX ¹ 0 *and* ZF = 0.
MOV	dest ¬ operand or data stored at operand address
MUL	Unsigned multiply (immediate operand not allowed) DX:AX ¬ AX * (word op), or AX ¬ AL * (byte op)	?	?	ü	ü	?	?
NEG	dest ¬ - dest	ü	ü	ü	ü	ü	ü
NOT	dest ¬ complement{dest}
OR	dest ¬ dest .OR. source	ü	ü	0	0	ü	?
OUT	port ¬ AL or AX operand is 8-bit immediate or DX
POP	dest ¬ contents of stack, SP ¬ SP + 2
POPF	flags ¬ contents of stack, SP ¬ SP + 2	ü	ü	ü	ü	ü	ü
PUSH	stack ¬ source, SP ¬ SP - 2
PUSHF	stack ¬ flags, SP ¬ SP - 2
RCL	rotate word or byte left including CF (9 bit or 17 bit rotate); source 1 or CL.			ü	?
RCR	rotate word or byte right including CF (9 bit or 17 bit rotate); source is 1 or CL.			ü	?
RET	CS:IP or IP ¬ stack
ROL	Rotate left 8 or 16 bit dest.; source is 1 or CL Bit rotated out is copied to CF			ü	?
ROR	Rotate right 8 or 16 bit dest.; source is 1 or CL Bit rotated out is copied to CF			ü	?
SAR	Shift right through CF with sign extension; source is 1 or CL	ü	ü	ü	?	ü	?
SBB	Subtract with borrow. dest ¬ dest - source - CF	ü	ü	ü	ü	ü	ü
SHL or SAL	Shift left dest through CF with 0 fill; source is 1 or CL	ü	ü	ü	?	ü	?
SHR	Shift right dest through CF with 0 fill; source is 1 or CL	0	ü	ü	?	ü	?
STC	CF ¬ 1			1
STI	Set interrupt enable flag. Maskable interrupts are serviced
SUB	dest ¬ dest - source	ü	ü	ü	ü	ü	ü
TEST	dest .AND. source	ü	ü	0	0	ü	?
XCHG	dest « source
XLAT	AL ¬ [DS:(BX + unsigned AL)]
XOR	dest ¬ dest .XOR. source	ü	ü	0	0	ü	?

Instructions Less Important to El E 485/486

Flags

AAA

ASCII adjust AL (carry into AH) after addition:

ASCII (0-9) + ASCII (0-9) ® Unpacked BCD

AAD

ASCII adjust before division (AX=10*AH +AL):

Unpacked BCD ® Binary

AAM

ASCII adjust after multiply

(AL/10: AH=Quo, AL=Rem)

Single digit BCD * Single digit BCD ® Unpacked BCD

AAS

ASCII adjust AL (borrow from AH) after subtraction:

ASCII (0-9) - ASCII (0-9) ® Unpacked BCD

CLD

Clear the direction bit.

String instructions increment SI and DI

CMPS

[DS:SI] - [ES:DI], update DI and SI (based on D flag)

CMPSB and CMPSW are size-specific

DAA

Decimal adjust AL after addition,

After a byte-wide add of packed BCD digits, adjusts AL to correct BCD result and sets C if result is > 9910

DAS

Decimal adjust after subtraction. Like DAA

ESC

put an operand on the data bus

HLT

stop the processor until a RESET or external interrupt

INTO

execute interrupt 4 if overflow flag is set

LAHF

Load AH from flags.

Bits (0,2,4,6,7) ¬ (CF, PF, AF, ZF, SF)

LDS

Load pointer using DS

DS:dest ¬ address of operand

LES

like LDS, except ES:dest receives address

LOCK

A prefix. Bus is locked until execution is completed

LODS

Load String. AX or AL ¬ [DS:SI], update SI

LODSB and LODSW are size-specific

MOVS

[ES:DI] ¬ [DS:SI], adjust SI and DI

MOVSB and MOVSW are size-specific

REP

A prefix. Like LOOP for string instructions.

REPE/REPZ and REPNE/REPNZ are also valid

SAHF

flags ¬ AH (used with LAHF)

SCAS

[ES:DI] - AL or AX. Update DI.

SCASB and SCASW are size-specific

STD

DF ¬ 1

String instructions decrement SI and DI

STOS

[ES:DI] ¬ AX or AL. Adjust DI.

STOSB and STOSW are size-specific

WAIT

processor idles processing interrupts until the external TEST line is asserted, then continues