The document describes the encoding of x86 machine code instructions. It provides examples of encoding for ADD, MOV, XOR, and other instructions. Each instruction encoding includes the opcode, register specification, addressing mode, and resulting machine code. Memory addresses are encoded using base, index, and displacement values.

1. (2)

3. 6- Then R/M = 100
0000001100000100
MACHINE CODE = 0304h
X X X X
ADD AX,[SI]
1- OPCODE = 000000
2- W=1 (16-BIT)
3- The REG is dest. i.e: D=1
4- then REG = 000 for AX
5- MOD =00
D
0
1
REG = code for Source reg
REG = code for Dest. reg
MODE

4. 6- Then R/M = 011
100010001100
000011
MACHINE CODE = 88C3h
X X X X
MOV BL,AL
1- OPCODE = 100010
2- W=0 (8-BIT)
3- Let REG be the source
i.e: D=0
4- then REG = 000 for AL
5- MOD =11
D
0
1
REG = code for Source reg
REG = code for Dest. reg
MODE
OR= 8AD8h (if D=1,REG=011&R/M=000)

5. 6- Then R/M = 110
0011001000001110
MACHINE CODE = 320E3412h
0011 01000001 0010
X X
XOR CL,[1234h]
1- OPCODE = 001100
2- W=0 (8-BIT)
3- The REG is dest. i.e:
D=1
4- then REG = 001 for CL
5- MOD =00
D
0
1
REG = code for Source reg
REG = code for Dest. reg
MODE

6. 6- Then R/M = 001
0000000110000001
MACHINE CODE = 01813412h
0011 01000001 0010
X X
ADD [BX][DI][1234],AX
1- OPCODE = 000000
2- W=1 (16-BIT)
3- The REG is source
i.e. D=0
4- then REG = 000 for AL
5- MOD =10
D
0
1
REG = code for Source reg
REG = code for Dest. reg
MODE

7. 6- Then R/M = 011
1100011110000011
MACHINE CODE = C7833412CDABh
0011 01000001 00101100 11011010 1011
MOV WORD PTR [BP][DI][1234],0ABCDh
1- OPCODE = 110001
2- W=1 (16-BIT)
3- D=1 from table
4- then REG = 000 from
table
5- MOD =10
MODE

8. 4- Then R/M = 011
1000110010011011
MACHINE CODE = 8CC9B3412h
0011 01000001 0010
X X
MOV [BP][DI][1234],DS
1- OPCODE = 10001100
2- then REG = 011 from
table
3- MOD =10
MODE

10. D
0
1
REG = code for Source reg
REG = code for Dest. reg
MODE