1. 80x86 Instruction Set
Dr. Qiang Lin

2. Overview
Most of assembler instructions presented are supported by all of the following Intel processors:
80186, 80286, 80386, 80486, Pentium (80586)
Five major instruction categories:
Transfer and Set
Arithmetic
Logic
Jump
Miscellaneous

3. 80x86 Transfer & Set Instructions 1

4. Transfer Instructions Examples 1
MOV AX,0006h ; Move immediate data to AX register
MOV BX,AX ; Move AX register data to BX register
This small program moves the value of 0006H to the AX register, then it
moves the content of AX (0006h) to the BX register
Example 2:
MOV AX,2000h ; Move immediate data to AX register
MOV DS,AX ; Load DS segment register
MOV SI, 100h ; Load immediate data to SI index register
MOV DI, 120h ; Load immediate data to DI index register
MOV CX, 10h ; Load immediate data to CX register
MOV AH, [SI], ; Move memory data pointed by [SI] to AH register
MOV [DI], AH ; Move AH register to memory located at [DI]

5. Set Instructions That Test Flags

6. Set Instructions for Unsigned Comparisons

7. Set Instructions for Signed Comparisons

8. Set Instructions Example
Bool := ((A <= B) and (D = E)) or (F <> G)
MOV AX, A
CMP AX, B
SETLE BL
MOV AX, D
CMP AX, E
SETE BH
AND BL, BH
MOV AX, F
CMP AX, G
SETNE BH
OR BL, BH
MOV Bool, BH

9. 80x86 Transfer Instructions 2

10. Transfer Instructions Examples 2
PUSH DS ; Push current DS content to stack
MOV AX,0 ; Move immediate data to AX register
PUSH AX ; Push 0 to stack
MOV AL, 0A1H
CBW
CWD
Example 2:
IN AL, 60h ; Read keyboard port
MOV DX,378h ; Point at LPT1: data port
IN AL, DX ; Read data from printer port
INC AX ; Bump ASCII code by one
OUT DX, AL ; Write data in AL to printer port

11. 80x86 String (Transfer) Instructions 3

12. 80x86 Arithmetic Instructions 1

13. Arithmetic Instructions Examples 1
Example 1: J = K + M
MOV AX, K
ADD AX,M
MOV J, AX
Example 2: J = K + M + N + P
ADD AX,N
ADD AX,P

14. Arithmetic Instructions Examples 2
Example 1: J = K - J
MOV AX, K
SUB J, AX
MOV J, AX
Example 1: J = J - (K + M)
MOV AX, J
SUB AX, K
SUB AX, M or
ADD AX, M

15. 80x86 Arithmetic Instructions 2

16. Arithmetic Instructions Examples 3
Example 1: ((J*7 + K) * 6 + M) * 2
MOV BX, J
IMUL BX, 7
ADD BX, K
IMUL BX, 6
ADD BX, M
ADD BX, BX
Example 2: J = K/ M (unsigned)
MOV AX, K
MOV DX, 0 ; Zero extend unsigned value in AX to DX
DIV M
MOV J, AX

17. 80x86 Arithmetic Instructions 3

18. SHL\SAL\SAR Instructions
Move each bit in destination operand one bit to left by No. of times specified by count operand
Zeros fill vacated positions at L.O. bit; H.O. bit shifts into carry flag
SHL AH, 4 ; Move L.O. bits to H.O. position
SAR
Move each bit in destination operand one bit to right by No. of times specified by count operand
H.O. bit fills vacated position at H.O. bit; L.O. bit shifts into carry flag
SAR AH, 4

19. RCL\RCR\ROL\ROR Instructions

20. 80x86 Logic Instructions 1

21. 80x86 Logic Instructions 2
Except NOT, AND, OR and XOR instructions affect flags as follows:
Clear carry flag
Clear overflow flag
Set zero flag if result is zero and clear it otherwise
Copy H.O. bit of result into sign flag
Set parity flag according to parity (number of one bits) in result
Scramble auxiliary carry flag
NOT instruction does not affect any flags

22. SHR\SHLD\SHRD Instructions
Provide double precision shift left and right operations, respectively
Available only on and later processors with forms of
SHLD operand1, operand2, immediate
SHLD operand1, operand2, CL
SHRD operand1, operand2, immediate
SHRD operand1, operand2, CL

23. SHRD Instruction Example
Let
ax contains a value in range representing a year ( )
bx contains a value in the range representing a day, and
cx contains a value in the range representing a month
Pack these data into dx as follows:
SHRD DX, AX, 7
SHRD DX, BX, 5
SHRD DX, CX, 4

24. 80x86 Miscellaneous Instructions
LEA - Loads specified 16 or 32 bit general purpose register with effective
address of the specified memory location using formats of:
LEA reg16, mem or LEA reg32, mem (only for or later processors)
Examples:
LEA AX, [BX]
LEA BX, 3[BX]
LEA AX, 3[BX]
LEA BX, 4[BP+SI]
LEA AX, -123[DI]

25. 80x86 General Jump Instructions 1

26. 80x86 General Jump Instructions 2

27. 80x86 Unsigned Jump (Cardinal) Instructions

28. 80x86 Signed Jump (Integer) Instructions

29. Jump Instructions Examples 1
POP AX
JMP AX
CALL SUB
CALL DwordTbl[BX]
SUB: PUSH AX
PUSH BX ….
POP BX
RET