A microprocessor is an electronic component that is used by a computer to do its work. It is a central processing unit on a single integrated circuit chip containing millions of very small components including transistors, resistors, and diodes that work together. Some microprocessors in the 20th century required several chips. Microprocessors help to do everything from controlling elevators to searching the Web. Everything a computer does is described by instructions of computer programs, and microprocessors carry out these instructions many millions of times a second. [1] Microprocessors were invented in the 1970s for use in embedded systems. The majority are still used that way, in such things as mobile phones, cars, military weapons, and home appliances. Some microprocessors are microcontrollers, so small and inexpensive that they are used to control very simple products like flashlights and greeting cards that play music when you open them. A few especially powerful microprocessors are used in personal computers.

1. Arithmetic Instructions

2. Arithmetic Instructions
• ADD Des, Src:
• It adds a byte to byte or a word to word.
• It effects AF, CF, OF, PF, SF, ZF flags.
• E.g.:
• ADD AL, 74H
• ADD DX, AX
• ADD AX, [BX]

3. Arithmetic Instructions
• ADC Des, Src:
• It adds the two operands with CF.
• It effects AF, CF, OF, PF, SF, ZF flags.
• E.g.:
• ADC AL, 74H
• ADC DX, AX
• ADC AX, [BX]

4. Arithmetic Instructions
• SUB Des, Src:
• It subtracts a byte from byte or a word from
word.
• It effects AF, CF, OF, PF, SF, ZF flags.
• For subtraction, CF acts as borrow flag.
• E.g.:
• SUB AL, 74H
• SUB DX, AX
• SUB AX, [BX]

5. Arithmetic Instructions
• SBB Des, Src:
• It subtracts the two operands and also the
borrow from the result.
• It effects AF, CF, OF, PF, SF, ZF flags.
• E.g.:
• SBB AL, 74H
• SBB DX, AX
• SBB AX, [BX]

6. Arithmetic Instructions
• INC Src:
• It increments the byte or word by one.
• The operand can be a register or memory
location.
• It effects AF, OF, PF, SF, ZF flags.
• CF is not effected.
• E.g.: INC AX

7. Arithmetic Instructions
• DEC Src:
• It decrements the byte or word by one.
• The operand can be a register or memory
location.
• It effects AF, OF, PF, SF, ZF flags.
• CF is not effected.
• E.g.: DEC AX

8. DAA (Decimal Adjust Accumulator)
Syntax :-- DAA
• This instruction is used to convert the result of the
addition of two packed BCD numbers to a valid BCD
number.
• The result has to be only in AL.
• After addition if the lower nibble is greater than 9 or
AF =1, it will add 06H to the lower nibble in AL.
• After this addition, if the upper nibble is greater than
9 or if CF = 1, DAA instruction adds 60H to AL.
• DAA instruction affects AF,CF,PF and ZF. OF is
undefined.

9. DAA Instruction contd..
• Operation Performed :--
– If lower nibble of AL > 9 or AF =1 then AL = AL +06
– If higher nibble of AL > 9 or CF =1 then AL = AL +60

10. Numeric Examples
AL = 53H, CL = 29H
ADD AL,CL ; AL  (AL) + (CL)
;AL  53 + 29
;AL  7CH
DAA ; AL 7C +06 (as C>9)
;AL 82

11. Numeric Examples
AL = 73H, CL = 29H
ADD AL,CL ; AL  (AL) + (CL)
;AL  73 + 29
;AL  9CH
DAA ; AL 02 and CF = 1 (as C>9)

12. DAS (Decimal Adjust After Subtraction)
Syntax :-- DAS
• This instruction is used to convert the result of the
subtraction of two packed BCD numbers to a valid BCD
number.
• The subtraction has to be only in AL.
• After subtraction if the lower nibble is greater than 9
or AF =1, it will subtract 06H from the lower nibble in
AL.
• If the result of the subtraction sets the carry flag or if
the upper nibble is greater than 9, DAS instruction
subtracts 60H from AL.
• DAS instruction affects AF,CF,PF and ZF. OF is
undefined.

13. DAS Instruction contd..
• Operation Performed :--
– If lower nibble of AL > 9 or AF =1 then AL = AL -06
– If higher nibble of AL > 9 or CF =1 then AL = AL -60

14. Numeric Examples
AL = 75, BH = 46
SUB AL,BH ; AL  (AL) - (BH)
;AL  75 - 46
;AL  2FH
; AF = 1
DAS ; AL 2F - 06 (as F>9)
;AL 29

15. Numeric Examples
AL = 38, BH = 61
SUB AL,BH ; AL  (AL) - (BH)
;AL  38 - 61
;AL  D7H
; CF = 1
DAS ; AL D7 - 60 (as D>9)
;AL 77

16. NEG ( Negate )
Syntax :-- NEG destination
• This instruction replaces the number in the
destination with the 2’s complement of that number.
• For obtaining the 2’s complement, it subtracts the
contents of destination from zero.
•The result is stored back in the destination which may
be a register or a memory location
• If OF =1, it indicates that the operation could not be
completed successfully.
• NEG instruction affects all conditional flags.

17. MUL (Unsigned multiplication)
Syntax :-- MUL source
• This instruction multiplies an unsigned byte
from source with an unsigned byte in AL
register
or
unsigned word from source with an unsigned
word in AX register.
• The source can be a register or memory
location but cannot be an immediate data.

18. MUL (Unsigned multiplication) Contd..
•When a byte is multiplied with a byte in AL, the
result is stored in AX.
• When a word is multiplied with a word in AX, the
MSW (Most Significant Word ) of the result is stored
in DX and the LSW (Least Significant Word ) of the
result is stored in AX.
• If MS Byte or Word of the result is zero, CF and OF
both will be set.
•All other flags are modified depending upon the
result

19. • Operation Performed :--
– If source is byte then AX  AL * unsigned 8 bit
source
– If source is word then DX, AX  AX * unsigned 16
bit source
Examples :--
1. MUL BL ; Multiply AL by BL & the result in AX
2. MUL CX ; Multiply AX by CX & the result in DX,AX
3. MUL Byte PTR [SI] ; AX  AL * [SI]
MUL (Unsigned multiplication) Contd..

20. IMUL (Signed multiplication)
Syntax :-- IMUL source
• This instruction multiplies a signed byte from
source with a signed byte in AL register
or
signed word from source with an signed word
in AX register.
• The source can be a register, general purpose,
base or index, or memory location, but cannot
be an immediate data.

21. IMUL (Signed multiplication) Contd..
•When a byte is multiplied with a byte in
AL, the result is stored in AX.
• When a word is multiplied with a word
in AX, the MSW (Most Significant Word )
of the result is stored in DX and the LSW
(Least Significant Word ) of the result is
stored in AX.

22. IMUL (Signed multiplication) Contd..
•If the magnitude of the product does not
require all the bits of the destination, the
unused bits are filled with copies of the sign
bit.
•If AH and DX contain parts of the 16 & 32 bit
results, CF and OF are set, If the unused bits
are filled by the sign bit, OF and CF are
cleared.

23. • Operation Performed :--
– If source is byte then AX  AL * signed 8 bit
source
– If source is word then DX, AX  AX * signed 16 bit
source
Examples :--
1. IMUL BL ; Multiply AL by BL & the result in AX
2. IMUL CX ; Multiply AX by CX & the result in DX,AX
3. IMUL Byte PTR [SI] ; AX  AL * [SI]
IMUL (Signed multiplication) Contd..

24. DIV (Unsigned Division)
Syntax :-- DIV source
• This instruction divides an unsigned word (16Bits)
in AX register by an unsigned byte (8Bits) from
source
or
an unsigned double word (32 bits) in DX & AX
register by an unsigned word (16bits) from source
• The source can be a register or memory location
but cannot be an immediate data.

25. DIV (Unsigned Division)Contd..
•When a word in AX is divided by a byte,
AL will contain the 8 bit quotient and AH
will contain an 8 bit remainder.
• When a double word in DX (MSW) &
AX (LSW) is divided by a word, AX will
contain the 16 bit quotient and DX will
contain an 16 bit remainder.

26. DIV (Unsigned Division)Contd..
•If a byte is to be divided by a byte, AL is
loaded with dividend and AH is filled with all
0’s.
•If a word is to be divided by a word, Ax is
loaded with dividend and DX is filled with all
0’s.
•If an attempt is made to divide by 0, or the
quotient is too large (FF or FFFF), type 0
interrupt is generated.
•No flags are affected.

27. • Operation Performed :--
–If source is byte then
• AL  AX / unsigned 8 bit source ; (quotient)
• AH  AX MOD unsigned 8 bit source ;
(remainder)
–If source is word then
• AX  DX:AX / unsigned 16 bit source ;
(quotient)
• DX  DX:AX MOD unsigned 16 bit source ;
(remainder)
DIV (Unsigned Division)Contd..

28. Examples :--
1. DIV BL ; Divide word in AX by byte in
BL, Quotient in AL, remainder
in AH.
2. DIV CX ; Divide double word in DX:AX
by word in CX, Quotient in AX,
Remainder in DX.
3. DIV [BX] ; Divide word in AX by byte in
memory location pointer by
BX.
DIV (Unsigned Division)Contd..

29. CBW (Convert Signed Byte to Word)
Syntax :-- CBW
• This instruction converts a signed byte
to a signed word.
•This instruction copies the sign of a byte
in AL to all the bits in AH.
• AH is then said to be the sign extension
of AL.
•CBW operation is done before
performing division of a signed byte in
the AL by another signed byte with IDIV
instruction.

30. CBW (Convert Signed Byte to Word) contd..
Operation :--
• AH  filled with 8th bit of AL i.e., D7
This does not affect any flags.
Example :--
If AX = 009BH, (00000000 10011011
After CBW Instruction,
AX =FF9B (11111111 10011011)

31. CWD (Convert Signed Word to Double Word)
Syntax :-- CWD
• This instruction copies the sign bit of a
word in AX to all the bits in DX.
• Thus the sign of AX is said to be
extended to DX.
•CWD operation is done before
performing division of a signed word in
the AX by another signed word with IDIV
instruction.

32. CWD (Convert Signed Word to Double Word) contd..
Operation :--
• DX filled with 16th bit of AX i.e., D15
This does not affect any flags.
Example :--
If DX = 0000H (00000000 00000000)
If AX = F0C7H, (11110000 11000111)
After CWD Instruction,
DX = FFFFH (11111111 11111111)
AX =F0C7 (11110000 11000111)

33. IDIV (Signed Division)
Syntax :-- IDIV source
• This instruction divides an signed word
(16Bits) in AX register by an signed byte (8Bits)
from source
or
An signed double word (32 bits) in DX & AX
register by an signed word (16bits) from
source
• The source can be a register or memory
location but cannot be an immediate data.

34. IDIV (Signed Division)Contd..
•When a word in AX is divided by a byte,
AL will contain the 8 bit quotient and AH
will contain an 8 bit remainder.
• When a double word in DX (MSW) &
AX (LSW) is divided by a word, AX will
contain the 16 bit quotient and DX will
contain an 16 bit remainder.

35. IDIV (Signed Division)Contd..
•If a byte is to be divided by a byte, AL is
loaded with dividend and AH is filled with all
0’s.
•If a word is to be divided by a word, Ax is
loaded with dividend and DX is filled with all
0’s.
•If an attempt is made to divide by 0, or the
quotient is too large (FF or FFFF), type 0
interrupt is generated.
•No flags are affected.

36. • Operation Performed :--
–If source is byte then
• AL  AX / unsigned 8 bit source ; (quotient)
• AH  AX MOD unsigned 8 bit source ;
(remainder)
–If source is byte then
• AX  DX:AX / unsigned 16 bit source ;
(quotient)
• DX  DX:AX MOD unsigned 16 bit source ;
(remainder)
IDIV (Signed Division)Contd..

37. Examples :--
1. IDIV BL ; Divide signed word in AX by
signed byte in BL, Quotient in
AL, remainder in AH.
2. IDIV CX ; Divide signed double word in
DX:AX by signed word in CX,
Quotient in AX, Remainder in
DX.
3. IDIV [BX] ; Divide signed word in AX by
signed byte in memory
location pointer by BX.
IDIV (Signed Division)Contd..

38. Example of division of a signed byte with
signed byte :--
MOV BL,divisor ; Load signed byte divisor in BL
MOV AL,dividend ; Load signed byte dividend in AL
CBW ;Extend sign of AL into AH
IDIV BL ; Byte division, Remainder in AH
and quotient in AL