1. Handout 2 Digital System Engineering (EE-390)
(Ref: Text book and
KFUPM Online course of EE-390)
(Remember to solve all the related examples,
exercises problems as given in the Syllabus)

2. MOV Statement 0202 01 00 IP CS SS DS ES AX BX CX DX SP BP SI DI SR
Mem. contents IP CS SS DS ES AX BX CX DX SP BP SI DI SR
0200
0100 XX
P.A’s
00000
01200 8C
MOV DX, CS
01201 CA
01202 XX
Next Instruction
01203
FFFFF
0202 01 00

3. Addressing Modes
Accumulator

4. A) Register Operand Addressing Mode
Mem. contents IP CS SS DS ES AX BX CX DX SP BP SI DI SR
02F0
0120 XX 1B D7
P.A’s
00000
014F0 8B
MOV AX, BX
014F1 C3
014F2 XX
Next Instruction
014F3
FFFFF
02F2 1B D7

5. A) Register Operand Addressing Mode
Mem. contents IP CS SS DS ES AX BX CX DX SP BP SI DI SR
0260
45A2 1B D7 XX
P.A’s
00000
45C80 8B
MOV DL, BH
45C81 C3
45C82 XX
Next Instruction
45C83
FFFFF
0262 1B

6. B) Immediate Operand Addressing Mode
Mem. contents IP CS SS DS ES AX BX CX DX SP BP SI DI SR
0400
0210 XX
P.A’s
00000
02500 B8
MOV AX, 4A1FH
02501 1F
02502 4A
02503 XX
Next Instruction
FFFFF
0403 4A 1F

7. B) Immediate Operand Addressing Mode
Mem. contents IP CS SS DS ES AX BX CX DX SP BP SI DI SR
0400
0210 XX
P.A’s
00000
02500 B6
MOV DH, 28H
02501 28
02502 XX
Next Instruction
FFFFF
0402 28 XX

8. Valid and Invalid Instructions
MOV CL, AH
 VALID
MOV CX, SP
 VALID
MOV CH, DX
 INVALID
MOV 15H, AL
 INVALID
MOV CL, 1234H
 INVALID
MOV IP, CX
 INVALID
MOV CS, DS
 INVALID
MOV CL, 234H
 INVALID

9. C) Memory Operand Addressing Mode
1) Direct Memory Addressing
2) Indirect Memory Addressing
a) Register Indirect Addressing
b) Based Addressing
c) Indexed Addressing
d) Based-Indexed Addressing

10. C) Memory Operand Addressing Mode
PA = Segment Base Address (SBA) : Effective Address (EA)
= SBA : EA
EA (called Effective or Offset) is EA = Base + Index + Displacement
PA = SBA : Base + Index + Displacement CS SS DS ES
PA = : BX BP SI DI
8-bit displacement
16-bit displacement

11. 1) Direct Addressing Mode
Mem. contents IP CS SS DS ES AX BX CX DX SP BP SI DI SR
0010
0320
6500 XX
P.A’s
00000
03210 8B
MOV CX, [52F1H]
03211 0E
03212 F1
03213 52
03214 XX
Next Instruction
6A2F1 = DS:52F1 3F
6A2F2= DS:52F2 D2
FFFFF
0012
Code segment D2 3F
data segment

12. 1) Direct Addressing Mode
Mem. contents IP CS SS DS ES AX BX CX DX SP BP SI DI SR
0010
0320
6500 XX
P.A’s
00000
03210 8A
MOV CH, [52F1H]
03211 2E
03212 F1
03213 52
03214 XX
Next Instruction
6500 : 52F1 = DS : 52F1 3F
FFFFF
0014 3F XX

13. 1) Direct Addressing Mode
Mem. contents IP CS SS DS ES AX BX CX DX SP BP SI DI SR
0010
0320
6500 52 XX
P.A’s
00000
03210 88
MOV [52F1H], CH
03211 2E
03212 F1
03213 52
03214 XX
Next Instruction
6500 : 52F1 = DS : 52F1
FFFFF
0014 52

14. 2) Register Indirect Addressing Mode
Mem. contents IP CS SS DS ES AX BX CX DX SP BP SI DI SR
0010
0320
6500 XX
0528
P.A’s
00000
03210 8B
MOV CX, [SI]
03211 1C
03212 XX
Next Instruction
03213
03214
6500 : 0528 = DS : SI 5D
6500 : 0529 = DS : SI + 1 CA
FFFFF
0012 CA 5D

15. 2) Register Indirect Addressing Mode
Mem. contents IP CS SS DS ES AX BX CX DX SP BP SI DI SR
0010
0320
6500 XX
0528
P.A’s
00000
03210 8A
MOV CL, [SI]
03211 0C
03212 XX
Next Instruction
03213
03214
6500 : 0528 = DS : SI 5D
FFFFF
0012 XX 5D

16. NOTE
By default, using a direct address as [1FA4H], or a register indirect address as [SI] or [DI] assumes you are accessing the DATA SEGMENT.
MOV AX, [1FA4H]  MOV AX, DS:[1FA4H]
To access any other segment, use the “SEGMENT OVERIDE PREFIX” as
MOV AX, CS:[1FA4H]
MOV SS:[DI] , AX

17. 3) Based Addressing Mode
Base Register  Points to first address of data (Constant)
Displacement  Contains number of bytes above base register where data of interest exists (Variable)
When Base Register is BX
PA = DS : BX + Displacement
When Base Register is BP
PA = SS : BP + Displacement
These are default segments and
Segment-Override Prefix changes them

18. 3) Based Addressing Mode
Mem. contents IP CS SS DS ES AX BX CX DX SP BP SI DI SR
0010
0320
2577
6500 XX 12 10
15F8
P.A’s
00000
03210 8A
MOV AL, [BX] + 2F10H
03211 87
03212 10
03213 2F
03214 XX
Next Instruction
6500 : F10 5D
FFFFF
0014 XX 5D

19. 3) Based Addressing Mode
Mem. contents IP CS SS DS ES AX BX CX DX SP BP SI DI SR
0010
0320
2577
6500 XX 12 10
15F8
P.A’s
00000
03210 8A
MOV AL, [BP] + 2F10H
03211 86
03212 10
03213 2F
03214 XX
Next Instruction
2577 : 15F8 + 2F10 5D
FFFFF
0014 XX 5D

20. 4) Indexed Addressing Mode
Displacement  Points to first address of data (Constant)
Index Register  Contains number of bytes above Displacement where data of interest exists (Variable)
When Index Register is SI
PA = DS : SI + Displacement
When Base Register is DI
PA = DS : DI + Displacement
These are default segments and
Segment-Override Prefix changes them

21. 4) Indexed Addressing Mode
Mem. contents IP CS SS DS ES AX BX CX DX SP BP SI DI SR
0010
0320
2577
523C XX
76FF
P.A’s
00000
03210 8A
MOV AL, [SI] + 2F10H
03211 84
03212 10
03213 2F
03214 XX
Next Instruction
523C : 76FF + 2F10 99
FFFFF
0014 XX 99

22. 4) Indexed Addressing Mode
Mem. contents IP CS SS DS ES AX BX CX DX SP BP SI DI SR
0010
0320
2577
766A 12 10
8DA5
P.A’s
00000
03210 89
MOV [DI] + 2F10H, BX
03211 9C
03212 10
03213 2F
03214 XX
Next Instruction
766A : 8DA5 + 2F10
766A : 8DA5 + 2F10 + 1
FFFFF
0014 10 12

23. 5) Based-Indexed Addressing Mode
Displacement  Points to first address of data (Constant)
Base Register  Contains Matrix Column Number (Variable)
Index Register  Contains Matrix Row Number (Variable)
Regardless of using SI or DI
When Base Register is BX
PA = DS : BX + (SI or DI) + Displacement
When Base Register is BP
PA = SS : BP + (SI or DI) + Displacement
These are default segments and
Segment-Override Prefix changes them

24. 5) Based-Indexed Addressing Mode
Mem. contents IP CS SS DS ES AX BX CX DX SP BP SI DI SR
0010
0320
2577
523C XX 12 34
76FF
P.A’s
00000
03210 8A
MOV AL, [BX][SI] + 2F10H
03211 80
03212 10
03213 2F
03214 XX
Next Instruction
523C : FF + 2F10 99
FFFFF
0014 XX 99

25. 5) Based-Indexed Addressing Mode
Mem. contents IP CS SS DS ES AX BX CX DX SP BP SI DI SR
0010
0320
2577
523C FF 77 12 34
76FF
P.A’s
00000
03210 89
MOV [BP][SI] + 2F10H, AX
03211 82
03212 10
03213 2F
03214 XX
Next Instruction
2577 : FF + 2F10
FFFFF
0014 FF 77