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]

 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]

 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]



 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]

 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

 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

 AAA (ASCII Adjust after Addition):

  •  The data entered from the terminal is in ASCII format.
  •  In ASCII, 0 – 9 are represented by 30H – 39H.
  •  This instruction allows us to add the ASCII codes.
  •  This instruction does not have any operand.

 Other ASCII Instructions:

  •  AAS (ASCII Adjust after Subtraction)
  •  AAM (ASCII Adjust after Multiplication)
  •  AAD (ASCII Adjust Before Division)


 DAA (Decimal Adjust after Addition)

  •  It is used to make sure that the result of adding two BCD numbers is adjusted to be a correct BCD number.
  •  It only works on AL register.


 DAS (Decimal Adjust after Subtraction)

  •  It is used to make sure that the result of subtracting two
  •  BCD numbers is adjusted to be a correct BCD number.
  •  It only works on AL register.



 NEG Src:

  •  It creates 2’s complement of a given number.
  •  That means, it changes the sign of a number.



 CMP Des, Src:

  •  It compares two specified bytes or words.
  •  The Src and Des can be a constant, register or memory location.
  •  Both operands cannot be a memory location at the same time.
  •  The comparison is done simply by internally subtracting the source from destination.
  •  The value of source and destination does not change, but the flags are modified to indicate the result.


 MUL Src:

  •  It is an unsigned multiplication instruction.
  •  It multiplies two bytes to produce a word or two words to produce a double word.
  •  AX = AL * Src
  •  DX : AX = AX * Src
  •  This instruction assumes one of the operand in AL or AX. 
  •  Src can be a register or memory location.


 IMUL Src:

  •  It is a signed multiplication instruction.



 DIV Src:

  •  It is an unsigned division instruction.
  •  It divides word by byte or double word by word.
  •  The operand is stored in AX, divisor is Src and the result is stored as:
  •  AH = remainder AL = quotient


 IDIV Src:

  •  It is a signed division instruction.


 CBW (Convert Byte to Word):

  •  This instruction converts byte in AL to word in AX.
  •  The conversion is done by extending the sign bit of AL throughout AH.


 CWD (Convert Word to Double Word):

  •  This instruction converts word in AX to double word in] DX : AX.
  •  The conversion is done by extending the sign bit of AX throughout DX.



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