1. Assembly Language Programming Part 2
Microprocessor’s Instruction Set

2. Microprocessor’s Instruction Set
An instruction set is a list of all the instructions, and all their variations, that a processor (or in the case of a virtual machine, an interpreter) can execute.
an instruction is a single operation of a processor defined by an instruction set architecture.
On traditional architectures, an instruction includes
An opcode specifying the operation to be performed, such as "add contents of memory to register",
zero or more operand specifiers, which may specify registers, memory locations, or literal data. The operand specifiers may have addressing modes determining their meaning or may be in fixed fields.

3. Microprocessor’s Instruction Set
Instructions include:
Arithmetic such as add and subtract
Logic instructions such as and, or, and not
Data instructions such as move, input, output, load, and store
Control flow instructions such as goto, if ... goto, call, and return.

4. MOV Operands Algorithm Examples
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).
Operands
Algorithm
Examples
REG, memory
memory, REG
REG, REG
memory, immediate
REG, immediate
SREG, memory
memory, SREG
REG, SREG
SREG, REG
operand1 = operand2
FLAGS
MOV has no impact on FLAGS register
MOV AL,[0100]
MOV [0100],AH
MOV AX,BX
MOV [0200],5
MOV BL,0EH
MOV DS, MyVar *
MOV MyVar, CS
MOV AX,ES
MOV SS,DX
* MyVar is a variable of size 2 bytes (Not available in Debug)

5. ADD Operands Algorithm Examples Add REG, memory memory, REG REG, REG
memory, immediate
REG, immediate
operand1 = operand1 + operand2
FLAGS
ADD AL,[0105]
ADD [0100],AH
ADD BX,CX
ADD [0200],5
ADD BL,1AH
ADD AL, MyVar *
ADD MyVar, DX **
* MyVar is a variable of size 1 bytes.
** MyVar is a variable of size 2 bytes.

6. INC Operands Algorithm Examples Increment. REG memory
operand = operand + 1
FLAGS
CF-Not changed
INC AL
INC [0100]
INC SI
INC CX
INC MyVar *
* MyVar is a variable of any size

7. SUB Operands Algorithm Examples Subtract REG, memory memory, REG
REG, REG
memory, immediate
REG, immediate
operand1 = operand1 - operand2
FLAGS
SUB AL,[0105]
SUB [0100],AH
SUB BX,CX
SUB [0200],5
SUB BL,1AH
SUB AL, MyVar *
SUB MyVar, DX **
* MyVar is a variable of size 1 bytes.
** MyVar is a variable of size 2 bytes.

8. DEC Operands Algorithm Examples Decrement. REG memory
operand = operand - 1
FLAGS
CF-Not changed
DEC AL
DEC [0100]
DEC SI
DEC CX
DEC MyVar *
* MyVar is a variable of any size

9. MUL Operands Algorithm Examples Unsigned multiply. REG memory
when operand is a byte: AX = AL * operand.
when operand is a word (2 Bytes): (DX AX) = AX * operand.
FLAGS
CF=OF=0 when high section of the result is zero.  
MUL BL
MUL [0302]
MUL BX
MUL MyVar *
* MyVar is a variable of any size

10. IMUL Operands Algorithm Examples Signed multiply. REG memory
when operand is a byte: AX = AL * operand.
when operand is a word (2 Bytes): (DX AX) = AX * operand.
FLAGS
CF=OF=0 when result fits into operand of IMUL. 
IMUL BL
IMUL [0302]
IMUL BX
IMUL MyVar *
* MyVar is a variable of any size

11. DIV Operands Algorithm Examples Unsigned divide. REG memory
when operand is a byte: AL = AX / operand AH = remainder (modulus)
when operand is a word: AX = (DX AX) / operand DX = remainder (modulus)
FLAGS
DIV BL
DIV [0302]
DIV BX
DIV MyVar *
* MyVar is a variable of any size

12. IDIV Operands Algorithm Examples Signed divide. REG memory
when operand is a byte: AL = AX / operand AH = remainder (modulus)
when operand is a word: AX = (DX AX) / operand DX = remainder (modulus)
FLAGS
IDIV BL
IDIV [0302]
IDIV BX
IDIV MyVar *
* MyVar is a variable of any size

13. NEG Operands Algorithm Examples
Negate. Makes operand negative (two's complement).
Operands
Algorithm
Examples
REG
memory
Invert all bits of the operand
Add 1 to inverted operand
FLAGS
NEG BL
NEG [0302]
NEG BX
NEG DI
NEG MyVar *
* MyVar is a variable of any size

14. NOP Operands Algorithm Examples No Operation. Do nothing No Operands
FLAGS

15. NOT Operands Algorithm Examples Invert each bit of the operand. REG
memory
if bit is 1 turn it to 0.
if bit is 0 turn it to 1.
FLAGS
NOT BL
NOT [0302]
NOT BX
NOT DI
NOT MyVar *
* MyVar is a variable of any size

16. AND Operands Algorithm Examples Logical 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
FLAGS
AND AL,[0105]
AND [0100],AH
AND BX,CX
AND [0200],5
AND BL,1AH
AND AL, MyVar *
AND MyVar, DX **
* MyVar is a variable of size 1 bytes.
** MyVar is a variable of size 2 bytes.

17. OR Operands Algorithm Examples Logical 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
FLAGS
OR AL,[0105]
OR [0100],AH
OR BX,CX
OR [0200],5
OR BL,1AH
OR AL, MyVar *
OR MyVar, DX **
* MyVar is a variable of size 1 bytes.
** MyVar is a variable of size 2 bytes.

18. XOR Operands Algorithm Examples Logical OR. 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
FLAGS
XOR AL,[0105]
XOR [0100],AH
XOR BX,CX
XOR [0200],5
XOR BL,1AH
XOR AL, MyVar *
XOR MyVar, DX **
* MyVar is a variable of size 1 bytes.
** MyVar is a variable of size 2 bytes.

19. SHL Operands Algorithm Examples
Shift operand1 Left. The number of shifts is set by operand2.
Operands
Algorithm
Examples
memory, immediate
REG, immediate
memory, CL
REG, CL
Shift all bits left, the bit that goes off is set to CF.
Zero bit is inserted to the right-most position.
FLAGS
OF=0 if first operand keeps original sign.
SHL [0105],2
SHL AH, 3
SHL [0200],CL
SHL BX, CL
SHL MyVar, 4 *
SHL MyVar, CL *
* MyVar is a variable of any size

20. SHR Operands Algorithm Examples
Shift operand1 Right. The number of shifts is set by operand2.
Operands
Algorithm
Examples
memory, immediate
REG, immediate
memory, CL
REG, CL
Shift all bits right, the bit that goes off is set to CF.
Zero bit is inserted to the left-most position.
FLAGS
OF=0 if first operand keeps original sign.
SHR [0105],2
SHR AH, 3
SHR [0200],CL
SHR BX, CL
SHR MyVar, 4 *
SHR MyVar, CL *
* MyVar is a variable of any size

21. ROL Operands Algorithm Examples
Rotate operand1 left. The number of rotates is set by operand2.
Operands
Algorithm
Examples
memory, immediate
REG, immediate
memory, CL
REG, CL
shift all bits left, the bit that goes off is set to CF and the same bit is inserted to the right-most position.
FLAGS
OF=0 if first operand keeps original sign.
ROL [0105],2
ROL AH, 3
ROL [0200],CL
ROL BX, CL
ROL MyVar, 4 *
ROL MyVar, CL *
* MyVar is a variable of any size

22. ROR Operands Algorithm Examples
Rotate operand1 right. The number of rotates is set by operand2.
Operands
Algorithm
Examples
memory, immediate
REG, immediate
memory, CL
REG, CL
shift all bits right, the bit that goes off is set to CF and the same bit is inserted to the left-most position.
FLAGS
OF=0 if first operand keeps original sign.
ROR [0105],2
ROR AH, 3
ROR [0200],CL
ROR BX, CL
ROR MyVar, 4 *
ROR MyVar, CL *
* MyVar is a variable of any size

23. XCHG Operands Algorithm Examples Exchange values of two operands.
REG, memory
memory, REG
REG, REG
operand1 < - > operand2
FLAGS
XCHG AL,[020E]
XCHG [020E], AL
XCHG AX,BX
XCHG DL,MyVar *
XCHG MyVar, BP **
* MyVar is a variable of size Byte
** MyVar is a variable of size Word

24. PUSH Operands Algorithm Examples
Store 16 bit value in the stack. Note: PUSH immediate works only on CPU and later!
Operands
Algorithm
Examples
REG
SREG
memory
immediate
SP = SP - 2
SS:[SP] (top of the stack) = operand
FLAGS
PUSH AX
PUSH CS
PUSH [020E]
PUSH 1AH
PUSH MyVar *
* MyVar is a variable of any size

25. POP Operands Algorithm Examples Get 16 bit value from the stack. REG
SREG
memory
operand = SS:[SP] (top of the stack)
SP = SP + 2
FLAGS
POP AX
POP CS
POP [020E]
POP MyVar *
* MyVar is a variable of any size

26. LOOP Operands Algorithm Examples
Decrease CX, jump to label if CX not zero.
Operands
Algorithm
Examples
Label/address
CX = CX - 1
if CX <> 0 then
jump
else
no jump, continue
FLAGS
MOV CX,5
label1:
; Some Code
LOOP label1
CS:0100 MOV CX,5
CS:0103 INC SI
CS:107 LOOP 103

27. CMP Operands Algorithm Examples Compare. REG, memory memory, REG
REG, REG
memory, immediate
REG, immediate
operand1 - operand2 result is not stored anywhere, flags are set (OF, SF, ZF, AF, PF, CF) according to result.
FLAGS
CMP DL,[021A]
CMP [021A], CL
CMP AX, DX
CMP [012A], 12H
CMP BL,0FH
CMP DL,MyVar *
CMP MyVar, BX **
* MyVar is a variable of size Byte
** MyVar is a variable of size Word

28. JMP Operands Algorithm Examples
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.
Operands
Algorithm
Examples
Label
address/4-byte address
always jump
FLAGS
label1:
; Some Code
JMP label1
CS:0100 JMP 104
CS:0104 INC SI

29. JE Operands Algorithm Examples
Short Jump if first operand is Equal to second operand (as set by CMP instruction). Signed/Unsigned.
Operands
Algorithm
Examples
Label
address
if ZF = 1 then jump
else continue
FLAGS
CMP AL,BL
JE label1
; Code to skip if ZF = 0
label1:
; Code to execute if ZF = 1
CS:0100 CMP AL,BL
CS:0102 JE 107
CS:0107 INC SI

30. JNE Operands Algorithm Examples
Short Jump if first operand is Not Equal to second operand (as set by CMP instruction). Signed/Unsigned.
Operands
Algorithm
Examples
Label
address
if ZF = 0 then jump
else continue
FLAGS
CMP AL,BL
JNE label1
; Code to skip if ZF = 1
label1:
; Code to execute if ZF = 0
CS:0100 CMP AL,BL
CS:0102 JNE 107
CS:0107 INC SI

31. JZ Operands Algorithm Examples
Short Jump if Zero (equal). Set by CMP, SUB, ADD, TEST, AND, OR, XOR instructions.
Operands
Algorithm
Examples
Label
address
if ZF = 1 then jump
else continue
FLAGS
CMP AL,BL
JZ label1
; Code to skip if ZF = 0
label1:
; Code to execute if ZF = 1
CS:0100 CMP AL,BL
CS:0102 JZ 107
CS:0107 INC SI

32. JNZ Operands Algorithm Examples
Short Jump if Not Zero (not equal). Set by CMP, SUB, ADD, TEST, AND, OR, XOR instructions.
Operands
Algorithm
Examples
Label
address
if ZF = 0 then jump
else continue
FLAGS
CMP AL,BL
JNZ label1
; Code to skip if ZF = 1
label1:
; Code to execute if ZF = 0
CS:0100 CMP AL,BL
CS:0102 JNZ 107
CS:0107 INC SI

33. JA Operands Algorithm Examples
Short Jump if first operand is Above second operand (as set by CMP instruction). Unsigned.
Operands
Algorithm
Examples
Label
address
if (CF = 0) and (ZF = 0) then jump
else continue
FLAGS
CMP AL,BL
JA label1
; Code to skip if CF <> 0 and
;ZF <> 0
label1:
; Code to execute if CF = 0 and
;ZF = 0
CS:0100 CMP AL,BL
CS:0102 JA 107
CS:0107 INC SI

34. JNA Operands Algorithm Examples
Short Jump if first operand is Not Above second operand (as set by CMP instruction). Unsigned.
Operands
Algorithm
Examples
Label
address
if CF = 1 or ZF = 1 then jump
else continue
FLAGS
CMP AL,BL
JNA label1
; Code to skip if CF <> 1 and
;ZF <> 1
label1:
; Code to execute if CF = 1 and
;ZF = 1
CS:0100 CMP AL,BL
CS:0102 JNA 107
CS:0107 INC SI

35. JAE Operands Algorithm Examples
Short Jump if first operand is Above or Equal to second operand (as set by CMP instruction). Unsigned.
Operands
Algorithm
Examples
Label
address
if CF = 0 then jump
else continue
FLAGS
CMP AL,BL
JAE label1
; Code to skip if CF <> 0
label1:
; Code to execute if CF = 0
CS:0100 CMP AL,BL
CS:0102 JAE 107
CS:0107 INC SI

36. JNAE Operands Algorithm Examples
Short Jump if first operand is Not Above and Not Equal to second operand (as set by CMP instruction). Unsigned.
Operands
Algorithm
Examples
Label
address
if CF = 1 then jump
else continue
FLAGS
CMP AL,BL
JNAE label1
; Code to skip if CF <> 1
label1:
; Code to execute if CF = 1
CS:0100 CMP AL,BL
CS:0102 JNAE 107
CS:0107 INC SI

37. JB Operands Algorithm Example if CF = 1 then jump
Short Jump if first operand is Below second operand (as set by CMP instruction). Unsigned.
Operands
Algorithm
Example
Label
address
if CF = 1 then jump
include 'emu8086.inc'
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

38. JBE Operands Algorithm Example
Short Jump if first operand is Below or Equal to second operand (as set by CMP instruction). Unsigned.
Operands
Algorithm
Example
Label
address
if CF = 1 or ZF = 1 then
jump
include 'emu8086.inc'
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

39. JNB Operands Algorithm Example
Short Jump if first operand is Not Below second operand (as set by CMP instruction). Unsigned.
Operands
Algorithm
Example
Label
address
if CF = 0 then jump
include 'emu8086.inc'
ORG 100h
MOV AL, 7
CMP AL, 5
JNB label1
PRINT 'AL < 5.'
JMP exit
label1:
PRINT 'AL >= 5.'
exit:
RET

40. JNBE Operands Algorithm Example
Short Jump if first operand is Not Below and Not Equal to second operand (as set by CMP instruction). Unsigned.
Operands
Algorithm
Example
Label
address
if (CF = 0) and (ZF = 0) then
jump
include 'emu8086.inc'
ORG 100h
MOV AL, 7
CMP AL, 5
JNBE label1
PRINT 'AL <= 5.'
JMP exit
label1:
PRINT 'AL > 5.'
exit:
RET

41. JG Operands Algorithm Example
Short Jump if first operand is Greater then second operand (as set by CMP instruction). Signed.
Operands
Algorithm
Example
Label
address
if (ZF = 0) and (SF = OF) then
jump
include 'emu8086.inc'
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

42. JGE Operands Algorithm Example include 'emu8086.inc'
Short Jump if first operand is Greater or Equal to second operand (as set by CMP instruction). Signed.
Operands
Algorithm
Example
Label
address
if SF = OF then jump
include 'emu8086.inc'
ORG 100h
MOV AL, 2
CMP AL, -5
JGE label1
PRINT 'AL < -5'
JMP exit
label1:
PRINT 'AL >= -5'
exit:
RET

43. JNG Operands Algorithm Example include 'emu8086.inc'
Short Jump if first operand is Not Greater then second operand (as set by CMP instruction). Signed.
Operands
Algorithm
Example
Label
address
if (ZF = 1) and (SF <> OF) then
jump
include 'emu8086.inc'
ORG 100h
MOV AL, 2
CMP AL, 3
JNG label1
PRINT 'AL > 3.'
JMP exit
label1:
PRINT 'Al <= 3.'
exit:
RET

44. JNGE Operands Algorithm Example include 'emu8086.inc'
Short Jump if first operand is Not Greater and Not Equal to second operand (as set by CMP instruction) Signed.
Operands
Algorithm
Example
Label
address
if SF <> OF then jump
include 'emu8086.inc'
ORG 100h
MOV AL, 2
CMP AL, 3
JNGE label1
PRINT 'AL >= 3.'
JMP exit
label1:
PRINT 'Al < 3.'
exit:
RET

45. JL Operands Algorithm Example
Short Jump if first operand is Less then second operand (as set by CMP instruction). Signed.
Operands
Algorithm
Example
Label
address
if SF <> OF then jump
include 'emu8086.inc'
ORG 100h
MOV AL, -2
CMP AL, 5
JL label1
PRINT 'AL >= 5.'
JMP exit
label1:
PRINT 'AL < 5.'
exit:
RET

46. JLE Operands Algorithm Example include 'emu8086.inc'
Short Jump if first operand is Less or Equal to second operand (as set by CMP instruction). Signed.
Operands
Algorithm
Example
Label
address
if SF <> OF or ZF = 1 then jump
include 'emu8086.inc'
ORG 100h
MOV AL, -2
CMP AL, 5
JLE label1
PRINT 'AL > 5.'
JMP exit
label1:
PRINT 'AL <= 5.'
exit:
RET

47. JNL Operands Algorithm Example
Short Jump if first operand is Not Less then second operand (as set by CMP instruction). Signed.
Operands
Algorithm
Example
Label
address
if SF = OF then jump
include 'emu8086.inc'
ORG 100h
MOV AL, 2
CMP AL, -3
JNL label1
PRINT 'AL < -3.'
JMP exit
label1:
PRINT 'Al >= -3.'
exit:
RET

48. JNLE Operands Algorithm Example
Short Jump if first operand is Not Less and Not Equal to second operand (as set by CMP instruction)Signed.
Operands
Algorithm
Example
Label
address
if (SF = OF) and (ZF = 0) then jump
include 'emu8086.inc'
ORG 100h
MOV AL, 2
CMP AL, -3
JNLE label1
PRINT 'AL <= -3.'
JMP exit
label1:
PRINT 'Al > -3.'
exit:
RET

49. Operands Algorithm Example
Label
address

50. Operands Algorithm Example
Label
address