Instruction Operands

Operand Description
reg An 8-, 16-, or 32-bit general register
reg8, reg16, reg32 A general register, identified by its number of bits
segreg A 16-bit segment register
mem A memory operand, using any of the standard memory addressing modes
mem8, mem16, mem32 A memory operand, identified by its number of bits
accum AL, AX, or EAX
immed An immediate operand
immed8, immed16, immed32 An immediate operand, identified by its number of bits
 An Immediate Operand  A Memory Operand  Dereference 
 
 
  .code
 
 
  mov   eax, -5000h
 
 
  call  WriteHex
 
 
 
  .data
 
 
  X  SDWORD  -5000h
 
 
  .code
 
 
  mov   eax, X
 
 
  call  WriteHex
 
 
 
  .data
 
 
  X  SDWORD  -5000h
 
 
  .code
 
 
  mov   eax, [X]
 
 
  call  WriteHex
 Output  Output  Output
   



   



   




 Offset  Dereference  Offset then Dereference 
 
 
  .data
 
 
  X  SDWORD  -5000h
 
 
  .code
 
 
  mov   eax, offset X
 
 
  call  WriteHex
 
 
 
  .data
 
 
  X  SDWORD  -5000h
 
 
  .code
 
 
  mov   eax, [offset X]
 
 
  call  WriteHex
 
 
 
  .data
 
 
  X  SDWORD  -5000h
 
 
  .code
 
 
  mov   ebx, offset X
 
 
  mov   eax, [ebx]
 
 
  call  WriteHex
 Output  Output  Output
   



   



   





ReadSub.asm 
COMMENT!
*
* This program reads and subtracts 32-bit hexadecimal integer from 50000h.
*
!

INCLUDE Irvine32.inc

.data
  prompt1  BYTE   0Dh, 0Ah, "Calculate an Arithmetic Expression of 50000h - Y:",
                  0Dh, 0Ah, 0
  prompt2  BYTE   "Enter the value of operand Y:   ", 0
  prompt3  BYTE   0Dh, 0Ah, "The result is  ", 0
  X        DWORD  50000h
  Y        DWORD  ?
  result   DWORD  ?
 
.code
main PROC
  mov    edx, OFFSET prompt1
  call   WriteString            ; print prompt1

  mov    edx, OFFSET prompt2
  call   WriteString            ; print prompt2

  call   ReadHex
  mov    Y, eax                 ; Y   = eax (the input)
  mov    eax, X                 ; eax = X (50000h)

  ; calculate 50000h – Y
  sub    eax, Y                 ; eax    = X (50000h) – Y (the input)
  mov    result, eax            ; result = eax (X – Y)

  mov    edx, OFFSET prompt3
  call   WriteString            ; print prompt3

  call   WriteHex               ; print eax (result)
  exit

main ENDP
END  main
An Execution Example 
 Calculate an Arithmetic Expression of 50000h – Y:
 Enter the value of operand Y:  4000 

 The result is  0004C000

†The white italic text with a navy background color is entered by users.




      “I am so clever that sometimes I don’t understand    
      a single word of what I am saying.”    
      — Oscar Wilde