Complete 8086 instruction set

Quick reference:

AAA
AAD
AAM
AAS
ADC
ADD
AND
CALL
CBW
CLC
CLD
CLI
CMC
CMP
CMPSB
CMPSW
CWD
DAA
DAS
DEC
DIV
HLT
IDIV
IMUL
IN
INC
INT
INTO
IRET
JA
JAE
JB
JBE
JC
JCXZ
JE
JG
JGE
JL
JLE
JMP
JNA
JNAE
JNB
JNBE
JNC
JNE
JNG
JNGE
JNL
JNLE
JNO
JNP
JNS
JNZ
JO
JP
JPE
JPO
JS
JZ
LAHF
LDS
LEA
LES
LODSB
LODSW
LOOP
LOOPE
LOOPNE
LOOPNZ
LOOPZ
MOV
MOVSB
MOVSW
MUL
NEG
NOP
NOT
OR
OUT
POP
POPA
POPF
PUSH
PUSHA
PUSHF
RCL
RCR
REP
REPE
REPNE
REPNZ
REPZ
RET
RETF
ROL
ROR
SAHF
SAL
SAR
SBB
SCASB
SCASW
SHL
SHR
STC
STD
STI
STOSB
STOSW
SUB
TEST
XCHG
XLATB
XOR


Operand types:

REG: AX, BX, CX, DX, AH, AL, BL, BH, CH, CL, DH, DL, DI, SI, BP, SP.

SREG: DS, ES, SS, and only as second operand: CS.

memory: [BX], [BX+SI+7], variable, etc...(see Memory Access).

immediate: 5, -24, 3Fh, 10001101b, etc...


Notes:




These marks are used to show the state of the flags:

1 - instruction sets this flag to 1.
0 - instruction sets this flag to 0.
r - flag value depends on result of the instruction.
? - flag value is undefined (maybe 1 or 0).




Some instructions generate exactly the same machine code, so disassembler may have a problem decoding to your original code. This is especially important for Conditional Jump instructions (see "Program Flow Control" in Tutorials for more information).




Instructions in alphabetical order:

Instruction Operands Description  
AAA No operands ASCII Adjust after Addition.
Corrects result in AH and AL after addition when working with BCD values.

It works according to the following Algorithm:

if low nibble of AL > 9 or AF = 1 then:
  • AL = AL + 6
  • AH = AH + 1
  • AF = 1
  • CF = 1
else
  • AF = 0
  • CF = 0
in both cases:
clear the high nibble of AL.

Example:
MOV AX, 15   ; AH = 00, AL = 0Fh
AAA          ; AH = 01, AL = 05
RET
C Z S O P A
r ? ? ? ? r
 
AAD No operands ASCII Adjust before Division.
Prepares two BCD values for division.

Algorithm:

  • AL = (AH * 10) + AL
  • AH = 0
Example:
MOV AX, 0105h   ; AH = 01, AL = 05
AAD             ; AH = 00, AL = 0Fh (15)
RET
C Z S O P A
? r r ? r ?
 
AAM No operands ASCII Adjust after Multiplication.
Corrects the result of multiplication of two BCD values.

Algorithm:

  • AH = AL / 10
  • AL = remainder
Example:
MOV AL, 15   ; AL = 0Fh
AAM          ; AH = 01, AL = 05
RET
C Z S O P A
? r r ? r ?
 
AAS No operands ASCII Adjust after Subtraction.
Corrects result in AH and AL after subtraction when working with BCD values.

Algorithm:

if low nibble of AL > 9 or AF = 1 then:
  • AL = AL - 6
  • AH = AH - 1
  • AF = 1
  • CF = 1
else
  • AF = 0
  • CF = 0
in both cases:
clear the high nibble of AL.

Example:
MOV AX, 02FFh  ; AH = 02, AL = 0FFh
AAS            ; AH = 01, AL = 09
RET
C Z S O P A
r ? ? ? ? r
 
ADC REG, memory
memory, REG
REG, REG
memory, immediate
REG, immediate 		Add with Carry.


Algorithm:

operand1 = operand1 + operand2 + CF

Example:
STC        ; set CF = 1
MOV AL, 5  ; AL = 5
ADC AL, 1  ; AL = 7
RET
C Z S O P A
r r r r r r
 
ADD REG, memory
memory, REG
REG, REG
memory, immediate
REG, immediate 		Add.


Algorithm:

operand1 = operand1 + operand2

Example:
MOV AL, 5   ; AL = 5
ADD AL, -3  ; AL = 2
RET
C Z S O P A
r r r r r r
 
AND REG, memory
memory, REG
REG, REG
memory, immediate
REG, immediate 		Logical AND between all bits of two operands. Result is stored in operand1.

These rules apply:

1 AND 1 = 1
1 AND 0 = 0
0 AND 1 = 0
0 AND 0 = 0

Example:
MOV AL, 'a'        ; AL = 01100001b
AND AL, 11011111b  ; AL = 01000001b  ('A')
RET
C Z S O P
0 r r 0 r
 
CALL procedure name
label
4-byte address
 		Transfers control to procedure, return address is (IP) is pushed to stack. 4-byte address may be entered in this form: 1234h:5678h, first value is a segment second value is an offset (this is a far call, so CS is also pushed to stack).


Example:
#make_COM#
ORG 100h  ; for COM file.

CALL p1

ADD AX, 1

RET         ; return to OS.

p1 PROC     ; procedure declaration.
    MOV AX, 1234h
    RET     ; return to caller.
p1 ENDP
C Z S O P A
unchanged
 
CBW No operands Convert byte into word.

Algorithm:

if high bit of AL = 1 then:
  • AH = 255 (0FFh)

else
  • AH = 0
Example:
MOV AX, 0   ; AH = 0, AL = 0
MOV AL, -5  ; AX = 000FBh (251)
CBW         ; AX = 0FFFBh (-5)
RET
C Z S O P A
unchanged
 
CLC No operands Clear Carry flag.

Algorithm:

CF = 0

C
0
 
CLD No operands Clear Direction flag. SI and DI will be incremented by chain instructions: CMPSB, CMPSW, LODSB, LODSW, MOVSB, MOVSW, STOSB, STOSW.

Algorithm:

DF = 0

D
0
 
CLI No operands Clear Interrupt enable flag. This disables hardware interrupts.

Algorithm:

IF = 0

I
0
 
CMC No operands Complement Carry flag. Inverts value of CF.

Algorithm:

if CF = 1 then CF = 0
if CF = 0 then CF = 1

C
r
 
CMP REG, memory
memory, REG
REG, REG
memory, immediate
REG, immediate 		Compare.

Algorithm:

operand1 - operand2

result is not stored anywhere, flags are set (OF, SF, ZF, AF, PF, CF) according to result.

Example:
MOV AL, 5
MOV BL, 5
CMP AL, BL  ; AL = 5, ZF = 1 (so equal!)
RET
C Z S O P A
r r r r r r
 
CMPSB No operands Compare bytes: ES:[DI] from DS:[SI].

Algorithm:

  • DS:[SI] - ES:[DI]
  • set flags according to result:
    OF, SF, ZF, AF, PF, CF
  • if DF = 0 then
    • SI = SI + 1
    • DI = DI + 1
    else
    • SI = SI - 1
    • DI = DI - 1
 Example:
see cmpsb.asm in Samples.

C Z S O P A
r r r r r r
 
CMPSW No operands Compare words: ES:[DI] from DS:[SI].

Algorithm:

  • DS:[SI] - ES:[DI]
  • set flags according to result:
    OF, SF, ZF, AF, PF, CF
  • if DF = 0 then
    • SI = SI + 2
    • DI = DI + 2
    else
    • SI = SI - 2
    • DI = DI - 2
 Example:
see cmpsw.asm in Samples.

C Z S O P A
r r r r r r
 
CWD No operands Convert Word to Double word.

Algorithm:

if high bit of AX = 1 then:
  • DX = 65535 (0FFFFh)

else
  • DX = 0
Example:
MOV DX, 0   ; DX = 0
MOV AX, 0   ; AX = 0
MOV AX, -5  ; DX AX = 00000h:0FFFBh
CWD         ; DX AX = 0FFFFh:0FFFBh
RET
C Z S O P A
unchanged
 
DAA No operands Decimal adjust After Addition.
Corrects the result of addition of two packed BCD values.

Algorithm:

if low nibble of AL > 9 or AF = 1 then:
  • AL = AL + 6
  • AF = 1
if AL > 9Fh or CF = 1 then:
  • AL = AL + 60h
  • CF = 1
Example:
MOV AL, 0Fh  ; AL = 0Fh (15)
DAA          ; AL = 15h
RET
C Z S O P A
r r r r r r
 
DAS No operands Decimal adjust After Subtraction.
Corrects the result of subtraction of two packed BCD values.

Algorithm:

if low nibble of AL > 9 or AF = 1 then:
  • AL = AL - 6
  • AF = 1
if AL > 9Fh or CF = 1 then:
  • AL = AL - 60h
  • CF = 1
Example:
MOV AL, 0FFh  ; AL = 0FFh (-1)
DAS           ; AL = 99h, CF = 1
RET
C Z S O P A
r r r r r r
 
DEC REG
memory
 		Decrement.

Algorithm:

operand = operand - 1


Example:
MOV AL, 255  ; AL = 0FFh (255 or -1)
DEC AL       ; AL = 0FEh (254 or -2)
RET
Z S O P A
r r r r r
CF - unchanged!  
DIV REG
memory
 		Unsigned divide.

Algorithm:

when operand is a byte:
AL = AX / operand
AH = remainder (modulus)
when operand is a word:
AX = (DX AX) / operand
DX = remainder (modulus)
Example:
MOV AX, 203   ; AX = 00CBh
MOV BL, 4
DIV BL        ; AL = 50 (32h), AH = 3
RET
C Z S O P A
? ? ? ? ? ?
 
HLT No operands Halt the System.

Example:
MOV AX, 5
HLT
C Z S O P A
unchanged
 
IDIV REG
memory
 		Signed divide.

Algorithm:

when operand is a byte:
AL = AX / operand
AH = remainder (modulus)
when operand is a word:
AX = (DX AX) / operand
DX = remainder (modulus)
Example:
MOV AX, -203 ; AX = 0FF35h
MOV BL, 4
IDIV BL      ; AL = -50 (0CEh), AH = -3 (0FDh)
RET
C Z S O P A
? ? ? ? ? ?
 
IMUL REG
memory
 		Signed multiply.

Algorithm:

when operand is a byte:
AX = AL * operand.
when operand is a word:
(DX AX) = AX * operand.
Example:
MOV AL, -2
MOV BL, -4
IMUL BL      ; AX = 8
RET
C Z S O P A
r ? ? r ? ?
CF=OF=0 when result fits into operand of IMUL.  
IN AL, im.byte
AL, DX
AX, im.byte
AX, DX 		Input from port into AL or AX.
Second operand is a port number. If required to access port number over 255 - DX register should be used.
Example:
IN AX, 4  ; get status of traffic lights.
IN AL, 7  ; get status of stepper-motor.
C Z S O P A
unchanged
 
INC REG
memory
 		Increment.

Algorithm:

operand = operand + 1

Example:
MOV AL, 4
INC AL       ; AL = 5
RET
Z S O P A
r r r r r
CF - unchanged!  
INT immediate byte Interrupt numbered by immediate byte (0..255).

Algorithm:

    Push to stack:
    • flags register
    • CS
    • IP
  • IF = 0
  • Transfer control to interrupt procedure
Example:
MOV AH, 0Eh  ; teletype.
MOV AL, 'A'
INT 10h      ; BIOS interrupt.
RET
C Z S O P A I
unchanged 0
  
INTO No operands Interrupt 4 if Overflow flag is 1.

Algorithm:

if OF = 1 then INT 4

Example:
; -5 - 127 = -132 (not in -128..127)
; the result of SUB is wrong (124),
; so OF = 1 is set:
MOV AL, -5
SUB AL, 127   ; AL = 7Ch (124)
INTO          ; process error.
RET
 
IRET No operands Interrupt Return.

Algorithm:

    Pop from stack:
    • IP
    • CS
    • flags register
C Z S O P A
popped
 
JA label Short Jump if first operand is Above second operand (as set by CMP instruction). Unsigned.

Algorithm:

    if (CF = 0) and (ZF = 0) then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 250
   CMP AL, 5
   JA label1
   PRINT 'AL is not above 5'
   JMP exit
label1:
   PRINT 'AL is above 5'
exit:
   RET
C Z S O P A
unchanged
 
JAE label Short Jump if first operand is Above or Equal to second operand (as set by CMP instruction). Unsigned.

Algorithm:

    if CF = 0 then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 5
   CMP AL, 5
   JAE label1
   PRINT 'AL is not above or equal to 5'
   JMP exit
label1:
   PRINT 'AL is above or equal to 5'
exit:
   RET
C Z S O P A
unchanged
 
JB label Short Jump if first operand is Below second operand (as set by CMP instruction). Unsigned.

Algorithm:

    if CF = 1 then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 1
   CMP AL, 5
   JB  label1
   PRINT 'AL is not below 5'
   JMP exit
label1:
   PRINT 'AL is below 5'
exit:
   RET
C Z S O P A
unchanged
 
JBE label Short Jump if first operand is Below or Equal to second operand (as set by CMP instruction). Unsigned.

Algorithm:

    if CF = 1 or ZF = 1 then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 5
   CMP AL, 5
   JBE  label1
   PRINT 'AL is not below or equal to 5'
   JMP exit
label1:
   PRINT 'AL is below or equal to 5'
exit:
   RET
C Z S O P A
unchanged
 
JC label Short Jump if Carry flag is set to 1.

Algorithm:

    if CF = 1 then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 255
   ADD AL, 1
   JC  label1
   PRINT 'no carry.'
   JMP exit
label1:
   PRINT 'has carry.'
exit:
   RET
C Z S O P A
unchanged
 
JCXZ label Short Jump if CX register is 0.

Algorithm:

    if CX = 0 then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV CX, 0
   JCXZ label1
   PRINT 'CX is not zero.'
   JMP exit
label1:
   PRINT 'CX is zero.'
exit:
   RET
C Z S O P A
unchanged
 
JE label Short Jump if first operand is Equal to second operand (as set by CMP instruction). Signed/Unsigned.

Algorithm:

    if ZF = 1 then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 5
   CMP AL, 5
   JE  label1
   PRINT 'AL is not equal to 5.'
   JMP exit
label1:
   PRINT 'AL is equal to 5.'
exit:
   RET
C Z S O P A
unchanged
 
JG label Short Jump if first operand is Greater then second operand (as set by CMP instruction). Signed.

Algorithm:

    if (ZF = 0) and (SF = OF) then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 5
   CMP AL, -5
   JG  label1
   PRINT 'AL is not greater -5.'
   JMP exit
label1:
   PRINT 'AL is greater -5.'
exit:
   RET
C Z S O P A
unchanged
 
JGE label Short Jump if first operand is Greater or Equal to second operand (as set by CMP instruction). Signed.

Algorithm:

    if SF = OF then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 2
   CMP AL, -5
   JGE  label1
   PRINT 'AL < -5'
   JMP exit
label1:
   PRINT 'AL >= -5'
exit:
   RET
C Z S O P A
unchanged
 
JL label Short Jump if first operand is Less then second operand (as set by CMP instruction). Signed.

Algorithm:

    if SF <> OF then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, -2
   CMP AL, 5
   JL  label1
   PRINT 'AL >= 5.'
   JMP exit
label1:
   PRINT 'AL < 5.'
exit:
   RET
C Z S O P A
unchanged
 
JLE label Short Jump if first operand is Less or Equal to second operand (as set by CMP instruction). Signed.

Algorithm:

    if SF <> OF or ZF = 1 then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, -2
   CMP AL, 5
   JLE label1
   PRINT 'AL > 5.'
   JMP exit
label1:
   PRINT 'AL <= 5.'
exit:
   RET
C Z S O P A
unchanged
 
JMP label
4-byte address
 		Unconditional Jump. Transfers control to another part of the program. 4-byte address may be entered in this form: 1234h:5678h, first value is a segment second value is an offset.


Algorithm:

    always jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 5
   JMP label1    ; jump over 2 lines!
   PRINT 'Not Jumped!'
   MOV AL, 0
label1:
   PRINT 'Got Here!'
   RET
C Z S O P A
unchanged
 
JNA label Short Jump if first operand is Not Above second operand (as set by CMP instruction). Unsigned.

Algorithm:

    if CF = 1 or ZF = 1 then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 2
   CMP AL, 5
   JNA label1
   PRINT 'AL is above 5.'
   JMP exit
label1:
   PRINT 'AL is not above 5.'
exit:
   RET
C Z S O P A
unchanged
 
JNAE label Short Jump if first operand is Not Above and Not Equal to second operand (as set by CMP instruction). Unsigned.

Algorithm:

    if CF = 1 then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 2
   CMP AL, 5
   JNAE label1
   PRINT 'AL >= 5.'
   JMP exit
label1:
   PRINT 'AL < 5.'
exit:
   RET
C Z S O P A
unchanged
 
JNB label Short Jump if first operand is Not Below second operand (as set by CMP instruction). Unsigned.

Algorithm:

    if CF = 0 then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 7
   CMP AL, 5
   JNB label1
   PRINT 'AL < 5.'
   JMP exit
label1:
   PRINT 'AL >= 5.'
exit:
   RET
C Z S O P A
unchanged
 
JNBE label Short Jump if first operand is Not Below and Not Equal to second operand (as set by CMP instruction). Unsigned.

Algorithm:

    if (CF = 0) and (ZF = 0) then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 7
   CMP AL, 5
   JNBE label1
   PRINT 'AL <= 5.'
   JMP exit
label1:
   PRINT 'AL > 5.'
exit:
   RET
C Z S O P A
unchanged
 
JNC label Short Jump if Carry flag is set to 0.

Algorithm:

    if CF = 0 then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 2
   ADD AL, 3
   JNC  label1
   PRINT 'has carry.'
   JMP exit
label1:
   PRINT 'no carry.'
exit:
   RET
C Z S O P A
unchanged
 
JNE label Short Jump if first operand is Not Equal to second operand (as set by CMP instruction). Signed/Unsigned.

Algorithm:

    if ZF = 0 then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 2
   CMP AL, 3
   JNE  label1
   PRINT 'AL = 3.'
   JMP exit
label1:
   PRINT 'Al <> 3.'
exit:
   RET
C Z S O P A
unchanged
 
JNG label Short Jump if first operand is Not Greater then second operand (as set by CMP instruction). Signed.

Algorithm:

    if (ZF = 1) and (SF <> OF) then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 2
   CMP AL, 3
   JNG  label1
   PRINT 'AL > 3.'
   JMP exit
label1:
   PRINT 'Al <= 3.'
exit:
   RET
C Z S O P A
unchanged
 
JNGE label Short Jump if first operand is Not Greater and Not Equal to second operand (as set by CMP instruction). Signed.

Algorithm:

    if SF <> OF then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 2
   CMP AL, 3
   JNGE  label1
   PRINT 'AL >= 3.'
   JMP exit
label1:
   PRINT 'Al < 3.'
exit:
   RET
C Z S O P A
unchanged
 
JNL label Short Jump if first operand is Not Less then second operand (as set by CMP instruction). Signed.

Algorithm:

    if SF = OF then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 2
   CMP AL, -3
   JNL label1
   PRINT 'AL < -3.'
   JMP exit
label1:
   PRINT 'Al >= -3.'
exit:
   RET
C Z S O P A
unchanged
 
JNLE label Short Jump if first operand is Not Less and Not Equal to second operand (as set by CMP instruction). Signed.

Algorithm:

    if (SF = OF) and (ZF = 0) then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 2
   CMP AL, -3
   JNLE label1
   PRINT 'AL <= -3.'
   JMP exit
label1:
   PRINT 'Al > -3.'
exit:
   RET
C Z S O P A
unchanged
 
JNO label Short Jump if Not Overflow.

Algorithm:

    if OF = 0 then jump
Example:
; -5 - 2 = -7 (inside -128..127)
; the result of SUB is correct,
; so OF = 0:

include 'emu8086.inc'
#make_COM#
ORG 100h
  MOV AL, -5
  SUB AL, 2   ; AL = 0F9h (-7)
JNO  label1
  PRINT 'overflow!'
JMP exit
label1:
  PRINT 'no overflow.'
exit:
  RET
C Z S O P A
unchanged
 
JNP label Short Jump if No Parity (odd). Only 8 low bits of result are checked. Set by CMP, SUB, ADD, TEST, AND, OR, XOR instructions.

Algorithm:

    if PF = 0 then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 00000111b   ; AL = 7
   OR  AL, 0           ; just set flags.
   JNP label1
   PRINT 'parity even.'
   JMP exit
label1:
   PRINT 'parity odd.'
exit:
   RET
C Z S O P A
unchanged
 
JNS label Short Jump if Not Signed (if positive). Set by CMP, SUB, ADD, TEST, AND, OR, XOR instructions.

Algorithm:

    if SF = 0 then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 00000111b   ; AL = 7
   OR  AL, 0           ; just set flags.
   JNS label1
   PRINT 'signed.'
   JMP exit
label1:
   PRINT 'not signed.'
exit:
   RET
C Z S O P A
unchanged
 
JNZ label Short Jump if Not Zero (not equal). Set by CMP, SUB, ADD, TEST, AND, OR, XOR instructions.

Algorithm:

    if ZF = 0 then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 00000111b   ; AL = 7
   OR  AL, 0           ; just set flags.
   JNZ label1
   PRINT 'zero.'
   JMP exit
label1:
   PRINT 'not zero.'
exit:
   RET
C Z S O P A
unchanged
 
JO label Short Jump if Overflow.

Algorithm:

    if OF = 1 then jump
Example:
; -5 - 127 = -132 (not in -128..127)
; the result of SUB is wrong (124),
; so OF = 1 is set:

include 'emu8086.inc'
#make_COM#
org 100h
  MOV AL, -5
  SUB AL, 127   ; AL = 7Ch (124)
JO  label1
  PRINT 'no overflow.'
JMP exit
label1:
  PRINT 'overflow!'
exit:
  RET
C Z S O P A
unchanged
 
JP label Short Jump if Parity (even). Only 8 low bits of result are checked. Set by CMP, SUB, ADD, TEST, AND, OR, XOR instructions.

Algorithm:

    if PF = 1 then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 00000101b   ; AL = 5
   OR  AL, 0           ; just set flags.
   JP label1
   PRINT 'parity odd.'
   JMP exit
label1:
   PRINT 'parity even.'
exit:
   RET
C Z S O P A
unchanged
 
JPE label Short Jump if Parity Even. Only 8 low bits of result are checked. Set by CMP, SUB, ADD, TEST, AND, OR, XOR instructions.

Algorithm:

    if PF = 1 then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 00000101b   ; AL = 5
   OR  AL, 0           ; just set flags.
   JPE label1
   PRINT 'parity odd.'
   JMP exit
label1:
   PRINT 'parity even.'
exit:
   RET
C Z S O P A
unchanged
 
JPO label Short Jump if Parity Odd. Only 8 low bits of result are checked. Set by CMP, SUB, ADD, TEST, AND, OR, XOR instructions.

Algorithm:

    if PF = 0 then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 00000111b   ; AL = 7
   OR  AL, 0           ; just set flags.
   JPO label1
   PRINT 'parity even.'
   JMP exit
label1:
   PRINT 'parity odd.'
exit:
   RET
C Z S O P A
unchanged
 
JS label Short Jump if Signed (if negative). Set by CMP, SUB, ADD, TEST, AND, OR, XOR instructions.

Algorithm:

    if SF = 1 then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 10000000b   ; AL = -128
   OR  AL, 0           ; just set flags.
   JS label1
   PRINT 'not signed.'
   JMP exit
label1:
   PRINT 'signed.'
exit:
   RET
C Z S O P A
unchanged
 
JZ label Short Jump if Zero (equal). Set by CMP, SUB, ADD, TEST, AND, OR, XOR instructions.

Algorithm:

    if ZF = 1 then jump
Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AL, 5
   CMP AL, 5
   JZ  label1
   PRINT 'AL is not equal to 5.'
   JMP exit
label1:
   PRINT 'AL is equal to 5.'
exit:
   RET
C Z S O P A
unchanged
 
LAHF No operands Load AH from 8 low bits of Flags register.

Algorithm:

    AH = flags register

AH bit:   7    6   5    4   3    2   1    0
        [SF] [ZF] [0] [AF] [0] [PF] [1] [CF]
bits 1, 3, 5 are reserved.

C Z S O P A
unchanged
 
LDS REG, memory Load memory double word into word register and DS.

Algorithm:

  • REG = first word
  • DS = second word
Example: 

#make_COM#
ORG 100h

LDS AX, m

RET

m  DW  1234h
   DW  5678h

END
AX is set to 1234h, DS is set to 5678h.

C Z S O P A
unchanged
 
LEA REG, memory Load Effective Address.

Algorithm:

  • REG = address of memory (offset)
Generally this instruction is replaced by MOV when assembling when possible.

Example: 

#make_COM#
ORG 100h

LEA AX, m

RET

m  DW  1234h

END
AX is set to: 0104h.
LEA instruction takes 3 bytes, RET takes 1 byte, we start at 100h, so the address of 'm' is 104h.

C Z S O P A
unchanged
 
LES REG, memory Load memory double word into word register and ES.

Algorithm:

  • REG = first word
  • ES = second word
Example: 

#make_COM#
ORG 100h

LES AX, m

RET

m  DW  1234h
   DW  5678h

END
AX is set to 1234h, ES is set to 5678h.

C Z S O P A
unchanged
 
LODSB No operands Load byte at DS:[SI] into AL. Update SI.

Algorithm:

  • AL = DS:[SI]
  • if DF = 0 then
    • SI = SI + 1
    else
    • SI = SI - 1
 Example: 
#make_COM#
ORG 100h

LEA SI, a1
MOV CX, 5
MOV AH, 0Eh

m: LODSB
INT 10h
LOOP m

RET

a1 DB 'H', 'e', 'l', 'l', 'o'
C Z S O P A
unchanged
 
LODSW No operands Load word at DS:[SI] into AX. Update SI.

Algorithm:

  • AX = DS:[SI]
  • if DF = 0 then
    • SI = SI + 2
    else
    • SI = SI - 2
 Example: 
#make_COM#
ORG 100h

LEA SI, a1
MOV CX, 5

REP LODSW   ; finally there will be 555h in AX.

RET

a1 dw 111h, 222h, 333h, 444h, 555h
C Z S O P A
unchanged
 
LOOP label Decrease CX, jump to label if CX not zero.

Algorithm:

  • CX = CX - 1
  • if CX <> 0 then
    • jump
    else
    • no jump, continue
 Example:
   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV CX, 5
label1:
   PRINTN 'loop!'
   LOOP label1
   RET
C Z S O P A
unchanged
 
LOOPE label Decrease CX, jump to label if CX not zero and Equal (ZF = 1).

Algorithm:

  • CX = CX - 1
  • if (CX <> 0) and (ZF = 1) then
    • jump
    else
    • no jump, continue
 Example:
; Loop until result fits into AL alone,
; or 5 times. The result will be over 255
; on third loop (100+100+100),
; so loop will exit.

   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AX, 0
   MOV CX, 5
label1:
   PUTC '*'
   ADD AX, 100
   CMP AH, 0
   LOOPE label1
   RET
C Z S O P A
unchanged
 
LOOPNE label Decrease CX, jump to label if CX not zero and Not Equal (ZF = 0).

Algorithm:

  • CX = CX - 1
  • if (CX <> 0) and (ZF = 0) then
    • jump
    else
    • no jump, continue
 Example:
; Loop until '7' is found,
; or 5 times.

   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV SI, 0
   MOV CX, 5
label1:
   PUTC '*'
   MOV AL, v1[SI]
   INC SI         ; next byte (SI=SI+1).
   CMP AL, 7
   LOOPNE label1
   RET
   v1 db 9, 8, 7, 6, 5
C Z S O P A
unchanged
 
LOOPNZ label Decrease CX, jump to label if CX not zero and ZF = 0.

Algorithm:

  • CX = CX - 1
  • if (CX <> 0) and (ZF = 0) then
    • jump
    else
    • no jump, continue
 Example:
; Loop until '7' is found,
; or 5 times.

   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV SI, 0
   MOV CX, 5
label1:
   PUTC '*'
   MOV AL, v1[SI]
   INC SI         ; next byte (SI=SI+1).
   CMP AL, 7
   LOOPNZ label1
   RET
   v1 db 9, 8, 7, 6, 5
C Z S O P A
unchanged
 
LOOPZ label Decrease CX, jump to label if CX not zero and ZF = 1.

Algorithm:

  • CX = CX - 1
  • if (CX <> 0) and (ZF = 1) then
    • jump
    else
    • no jump, continue
 Example:
; Loop until result fits into AL alone,
; or 5 times. The result will be over 255
; on third loop (100+100+100),
; so loop will exit.

   include 'emu8086.inc'
   #make_COM#
   ORG 100h
   MOV AX, 0
   MOV CX, 5
label1:
   PUTC '*'
   ADD AX, 100
   CMP AH, 0
   LOOPZ label1
   RET
C Z S O P A
unchanged
 
MOV REG, memory
memory, REG
REG, REG
memory, immediate
REG, immediate

SREG, memory
memory, SREG
REG, SREG
SREG, REG 		Copy operand2 to operand1.

The MOV instruction cannot:
  • set the value of the CS and IP registers.
  • copy value of one segment register to another segment register (should copy to general register first).
  • copy immediate value to segment register (should copy to general register first).

Algorithm:

operand1 = operand2
Example:
#make_COM#
ORG 100h
MOV AX, 0B800h    ; set AX = B800h (VGA memory).
MOV DS, AX        ; copy value of AX to DS.
MOV CL, 'A'       ; CL = 41h (ASCII code).
MOV CH, 01011111b ; CL = color attribute.
MOV BX, 15Eh      ; BX = position on screen.
MOV [BX], CX      ; w.[0B800h:015Eh] = CX.
RET               ; returns to operating system.
C Z S O P A
unchanged
 
MOVSB No operands Copy byte at DS:[SI] to ES:[DI]. Update SI and DI.

Algorithm:

  • ES:[DI] = DS:[SI]
  • if DF = 0 then
    • SI = SI + 1
    • DI = DI + 1
    else
    • SI = SI - 1
    • DI = DI - 1
 Example:
#make_COM#
ORG 100h

LEA SI, a1
LEA DI, a2
MOV CX, 5
REP MOVSB

RET

a1 DB 1,2,3,4,5
a2 DB 5 DUP(0)
C Z S O P A
unchanged
 
MOVSW No operands Copy byte at DS:[SI] to ES:[DI]. Update SI and DI.

Algorithm:

  • ES:[DI] = DS:[SI]
  • if DF = 0 then
    • SI = SI + 2
    • DI = DI + 2
    else
    • SI = SI - 2
    • DI = DI - 2
 Example:
#make_COM#
ORG 100h

LEA SI, a1
LEA DI, a2
MOV CX, 5
REP MOVSW

RET

a1 DW 1,2,3,4,5
a2 DW 5 DUP(0)
C Z S O P A
unchanged
 
MUL REG
memory
 		Unsigned multiply.

Algorithm:

when operand is a byte:
AX = AL * operand.
when operand is a word:
(DX AX) = AX * operand.
Example:
MOV AL, 200   ; AL = 0C8h
MOV BL, 4
MUL BL        ; AX = 0320h (800)
RET
C Z S O P A
r ? ? r ? ?
CF=OF=0 when high section of the result is zero.  
NEG REG
memory
 		Negate. Makes operand negative (two's complement).

Algorithm:

  • Invert all bits of the operand
  • Add 1 to inverted operand
 Example:
MOV AL, 5   ; AL = 05h
NEG AL      ; AL = 0FBh (-5)
NEG AL      ; AL = 05h (5)
RET
C Z S O P A
r r r r r r
 
NOP No operands No Operation.

Algorithm:

  • Do nothing
 Example:
; do nothing, 3 times:
NOP
NOP
NOP
RET
C Z S O P A
unchanged
 
NOT REG
memory
 		Invert each bit of the operand.

Algorithm:

  • if bit is 1 turn it to 0.
  • if bit is 0 turn it to 1.
 Example:
MOV AL, 00011011b
NOT AL   ; AL = 11100100b
RET
C Z S O P A
unchanged
 
OR REG, memory
memory, REG
REG, REG
memory, immediate
REG, immediate 		Logical OR between all bits of two operands. Result is stored in first operand.

These rules apply:

1 OR 1 = 1
1 OR 0 = 1
0 OR 1 = 1
0 OR 0 = 0

Example:
MOV AL, 'A'       ; AL = 01000001b
OR AL, 00100000b  ; AL = 01100001b  ('a')
RET
C Z S O P A
0 r r 0 r ?
 
OUT im.byte, AL
im.byte, AX
DX, AL
DX, AX 		Output from AL or AX to port.
First operand is a port number. If required to access port number over 255 - DX register should be used.

Example:
MOV AX, 0FFFh ; Turn on all
OUT 4, AX     ; traffic lights.

MOV AL, 100b  ; Turn on the third
OUT 7, AL     ; magnet of the stepper-motor.
C Z S O P A
unchanged
 
POP REG
SREG
memory 		Get 16 bit value from the stack.

Algorithm:

  • operand = SS:[SP] (top of the stack)
  • SP = SP + 2
Example:
MOV AX, 1234h
PUSH AX
POP  DX     ; DX = 1234h
RET
C Z S O P A
unchanged
 
POPA No operands Pop all general purpose registers DI, SI, BP, SP, BX, DX, CX, AX from the stack.
SP value is ignored, it is Popped but not set to SP register).

Note: this instruction works only on 80186 CPU and later!

Algorithm:

  • POP DI
  • POP SI
  • POP BP
  • POP xx (SP value ignored)
  • POP BX
  • POP DX
  • POP CX
  • POP AX
C Z S O P A
unchanged
 
POPF No operands Get flags register from the stack.

Algorithm:

  • flags = SS:[SP] (top of the stack)
  • SP = SP + 2
C Z S O P A
popped
 
PUSH REG
SREG
memory
immediate 		Store 16 bit value in the stack.

Note: PUSH immediate works only on 80186 CPU and later!

Algorithm:

  • SP = SP - 2
  • SS:[SP] (top of the stack) = operand
Example:
MOV AX, 1234h
PUSH AX
POP  DX     ; DX = 1234h
RET
C Z S O P A
unchanged
 
PUSHA No operands Push all general purpose registers AX, CX, DX, BX, SP, BP, SI, DI in the stack.
Original value of SP register (before PUSHA) is used.

Note: this instruction works only on 80186 CPU and later!

Algorithm:

  • PUSH AX
  • PUSH CX
  • PUSH DX
  • PUSH BX
  • PUSH SP
  • PUSH BP
  • PUSH SI
  • PUSH DI
C Z S O P A
unchanged
 
PUSHF No operands Store flags register in the stack.

Algorithm:

  • SP = SP - 2
  • SS:[SP] (top of the stack) = flags
C Z S O P A
unchanged
 
RCL memory, immediate
REG, immediate

memory, CL
REG, CL 		Rotate operand1 left through Carry Flag. The number of rotates is set by operand2.
When immediate is greater then 1, assembler generates several RCL xx, 1 instructions because 8086 has machine code only for this instruction (the same principle works for all other shift/rotate instructions).

Algorithm:

    shift all bits left, the bit that goes off is set to CF and previous value of CF is inserted to the right-most position.

Example:
STC               ; set carry (CF=1).
MOV AL, 1Ch       ; AL = 00011100b
RCL AL, 1         ; AL = 00111001b,  CF=0.
RET
C O
r r
OF=0 if first operand keeps original sign.  
RCR memory, immediate
REG, immediate

memory, CL
REG, CL 		Rotate operand1 right through Carry Flag. The number of rotates is set by operand2.

Algorithm:

    shift all bits right, the bit that goes off is set to CF and previous value of CF is inserted to the left-most position.

Example:
STC               ; set carry (CF=1).
MOV AL, 1Ch       ; AL = 00011100b
RCR AL, 1         ; AL = 10001110b,  CF=0.
RET
C O
r r
OF=0 if first operand keeps original sign.  
REP chain instruction
 		Repeat following MOVSB, MOVSW, LODSB, LODSW, STOSB, STOSW instructions CX times.

Algorithm:

check_cx:

if CX <> 0 then
  • do following chain instruction
  • CX = CX - 1
  • go back to check_cx
else
  • exit from REP cycle
Z
r
 
REPE chain instruction
 		Repeat following CMPSB, CMPSW, SCASB, SCASW instructions while ZF = 1 (result is Equal), maximum CX times.

Algorithm:

check_cx:

if CX <> 0 then
  • do following chain instruction
  • CX = CX - 1
  • if ZF = 1 then:
    • go back to check_cx
    else
    • exit from REPE cycle
else
  • exit from REPE cycle
 Example:
see cmpsb.asm in Samples.

Z
r
 
REPNE chain instruction
 		Repeat following CMPSB, CMPSW, SCASB, SCASW instructions while ZF = 0 (result is Not Equal), maximum CX times.

Algorithm:

check_cx:

if CX <> 0 then
  • do following chain instruction
  • CX = CX - 1
  • if ZF = 0 then:
    • go back to check_cx
    else
    • exit from REPNE cycle
else
  • exit from REPNE cycle
Z
r
 
REPNZ chain instruction
 		Repeat following CMPSB, CMPSW, SCASB, SCASW instructions while ZF = 0 (result is Not Zero), maximum CX times.

Algorithm:

check_cx:

if CX <> 0 then
  • do following chain instruction
  • CX = CX - 1
  • if ZF = 0 then:
    • go back to check_cx
    else
    • exit from REPNZ cycle
else
  • exit from REPNZ cycle
Z
r
 
REPZ chain instruction
 		Repeat following CMPSB, CMPSW, SCASB, SCASW instructions while ZF = 1 (result is Zero), maximum CX times.

Algorithm:

check_cx:

if CX <> 0 then
  • do following chain instruction
  • CX = CX - 1
  • if ZF = 1 then:
    • go back to check_cx
    else
    • exit from REPZ cycle
else
  • exit from REPZ cycle
Z
r
 
RET No operands
or even immediate		 Return from near procedure.

Algorithm:

  • Pop from stack:
    • IP
  • if immediate operand is present: SP = SP + operand
Example:
#make_COM#
ORG 100h  ; for COM file.

CALL p1

ADD AX, 1

RET         ; return to OS.

p1 PROC     ; procedure declaration.
    MOV AX, 1234h
    RET     ; return to caller.
p1 ENDP
C Z S O P A
unchanged
 
RETF No operands
or even immediate		 Return from Far procedure.

Algorithm:

  • Pop from stack:
    • IP
    • CS
  • if immediate operand is present: SP = SP + operand
C Z S O P A
unchanged
 
ROL memory, immediate
REG, immediate

memory, CL
REG, CL 		Rotate operand1 left. The number of rotates is set by operand2.

Algorithm:

    shift all bits left, the bit that goes off is set to CF and the same bit is inserted to the right-most position.
Example:
MOV AL, 1Ch       ; AL = 00011100b
ROL AL, 1         ; AL = 00111000b,  CF=0.
RET
C O
r r
OF=0 if first operand keeps original sign.  
ROR memory, immediate
REG, immediate

memory, CL
REG, CL 		Rotate operand1 right. The number of rotates is set by operand2.

Algorithm:

    shift all bits right, the bit that goes off is set to CF and the same bit is inserted to the left-most position.
Example:
MOV AL, 1Ch       ; AL = 00011100b
ROR AL, 1         ; AL = 00001110b,  CF=0.
RET
C O
r r
OF=0 if first operand keeps original sign.  
SAHF No operands Store AH register into low 8 bits of Flags register.

Algorithm:

    flags register = AH

AH bit:   7    6   5    4   3    2   1    0
        [SF] [ZF] [0] [AF] [0] [PF] [1] [CF]
bits 1, 3, 5 are reserved.

C Z S O P A
r r r r r r
 
SAL memory, immediate
REG, immediate

memory, CL
REG, CL 		Shift Arithmetic operand1 Left. The number of shifts is set by operand2.

Algorithm:

  • Shift all bits left, the bit that goes off is set to CF.
  • Zero bit is inserted to the right-most position.
 Example:
MOV AL, 0E0h      ; AL = 11100000b
SAL AL, 1         ; AL = 11000000b,  CF=1.
RET
C O
r r
OF=0 if first operand keeps original sign.  
SAR memory, immediate
REG, immediate

memory, CL
REG, CL 		Shift Arithmetic operand1 Right. The number of shifts is set by operand2.

Algorithm:

  • Shift all bits right, the bit that goes off is set to CF.
  • The sign bit that is inserted to the left-most position has the same value as before shift.
 Example:
MOV AL, 0E0h      ; AL = 11100000b
SAR AL, 1         ; AL = 11110000b,  CF=0.

MOV BL, 4Ch       ; BL = 01001100b
SAR BL, 1         ; BL = 00100110b,  CF=0.

RET
C O
r r
OF=0 if first operand keeps original sign.  
SBB REG, memory
memory, REG
REG, REG
memory, immediate
REG, immediate 		Subtract with Borrow.

Algorithm:

operand1 = operand1 - operand2 - CF

Example:
STC
MOV AL, 5
SBB AL, 3    ; AL = 5 - 3 - 1 = 1

RET
C Z S O P A
r r r r r r
 
SCASB No operands Compare bytes: AL from ES:[DI].

Algorithm:

  • ES:[DI] - AL
  • set flags according to result:
    OF, SF, ZF, AF, PF, CF
  • if DF = 0 then
    • DI = DI + 1
    else
    • DI = DI - 1
C Z S O P A
r r r r r r
 
SCASW No operands Compare words: AX from ES:[DI].

Algorithm:

  • ES:[DI] - AX
  • set flags according to result:
    OF, SF, ZF, AF, PF, CF
  • if DF = 0 then
    • DI = DI + 2
    else
    • DI = DI - 2
C Z S O P A
r r r r r r
 
SHL memory, immediate
REG, immediate

memory, CL
REG, CL 		Shift operand1 Left. The number of shifts is set by operand2.

Algorithm:

  • Shift all bits left, the bit that goes off is set to CF.
  • Zero bit is inserted to the right-most position.
 Example:
MOV AL, 11100000b
SHL AL, 1         ; AL = 11000000b,  CF=1.

RET
C O
r r
OF=0 if first operand keeps original sign.  
SHR memory, immediate
REG, immediate

memory, CL
REG, CL 		Shift operand1 Right. The number of shifts is set by operand2.

Algorithm:

  • Shift all bits right, the bit that goes off is set to CF.
  • Zero bit is inserted to the left-most position.
 Example:
MOV AL, 00000111b
SHR AL, 1         ; AL = 00000011b,  CF=1.

RET
C O
r r
OF=0 if first operand keeps original sign.  
STC No operands Set Carry flag.

Algorithm:

CF = 1

C
1
 
STD No operands Set Direction flag. SI and DI will be decremented by chain instructions: CMPSB, CMPSW, LODSB, LODSW, MOVSB, MOVSW, STOSB, STOSW.

Algorithm:

DF = 1

D
1
 
STI No operands Set Interrupt enable flag. This enables hardware interrupts.

Algorithm:

IF = 1

I
1
 
STOSB No operands Store byte in AL into ES:[DI]. Update SI.

Algorithm:

  • ES:[DI] = AL
  • if DF = 0 then
    • DI = DI + 1
    else
    • DI = DI - 1
 Example: 
#make_COM#
ORG 100h

LEA DI, a1
MOV AL, 12h
MOV CX, 5

REP STOSB

RET

a1 DB 5 dup(0)
C Z S O P A
unchanged
 
STOSW No operands Store word in AX into ES:[DI]. Update SI.

Algorithm:

  • ES:[DI] = AX
  • if DF = 0 then
    • DI = DI + 2
    else
    • DI = DI - 2
 Example: 
#make_COM#
ORG 100h

LEA DI, a1
MOV AX, 1234h
MOV CX, 5

REP STOSW

RET

a1 DW 5 dup(0)
C Z S O P A
unchanged
 
SUB REG, memory
memory, REG
REG, REG
memory, immediate
REG, immediate 		Subtract.

Algorithm:

operand1 = operand1 - operand2

Example:
MOV AL, 5
SUB AL, 1         ; AL = 4

RET
C Z S O P A
r r r r r r
 
TEST REG, memory
memory, REG
REG, REG
memory, immediate
REG, immediate 		Logical AND between all bits of two operands for flags only. These flags are effected: ZF, SF, PF. Result is not stored anywhere.

These rules apply:

1 AND 1 = 1
1 AND 0 = 0
0 AND 1 = 0
0 AND 0 = 0

Example:
MOV AL, 00000101b
TEST AL, 1         ; ZF = 0.
TEST AL, 10b       ; ZF = 1.
RET
C Z S O P
0 r r 0 r
 
XCHG REG, memory
memory, REG
REG, REG 		Exchange values of two operands.

Algorithm:

operand1 < - > operand2

Example:
MOV AL, 5
MOV AH, 2
XCHG AL, AH   ; AL = 2, AH = 5
XCHG AL, AH   ; AL = 5, AH = 2
RET
C Z S O P A
unchanged
 
XLATB No operands Translate byte from table.
Copy value of memory byte at DS:[BX + unsigned AL] to AL register.

Algorithm:

AL = DS:[BX + unsigned AL]

Example:
#make_COM#
ORG 100h
LEA BX, dat
MOV AL, 2
XLATB     ; AL = 33h

RET

dat DB 11h, 22h, 33h, 44h, 55h
C Z S O P A
unchanged
 
XOR REG, memory
memory, REG
REG, REG
memory, immediate
REG, immediate 		Logical XOR (Exclusive OR) between all bits of two operands. Result is stored in first operand.

These rules apply:

1 XOR 1 = 0
1 XOR 0 = 1
0 XOR 1 = 1
0 XOR 0 = 0

Example:
MOV AL, 00000111b
XOR AL, 00000010b    ; AL = 00000101b
RET
C Z S O P A
0 r r 0 r ?





Copyright © 2002 emu8086, Inc.
All rights reserved.
http://www.emu8086.com