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Lect 3: Instruction Set and Addressing Modes

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Title: Lect 4: Instruction Set and Addressing Modes Author: maeng Last modified by: maeng Created Date: 9/8/1998 2:07:52 AM Document presentation format – PowerPoint PPT presentation

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Title: Lect 3: Instruction Set and Addressing Modes


1
Lect 3 Instruction Set and Addressing Modes
2
386 Instruction Set (3.4)
  • Basic Instruction Set 8086/8088 instruction set
  • Extended Instruction Set 80286 several new
    instructions and additional addressing modes
  • 80386 specific instruction set

80386
80286
8086/8088
Protected Mode
System control Instruction set
System control Instruction set
Basic Extended 80386 specific Instruction Set
Basic Extended Instruction Set
Basic Instruction Set
Real Mode
3
386 Instruction Set (3.4)
  • Addressing Modes of 386DX (3.5)
  • Addressing Modes a method of specifying an
    operand
  • Operands in REG, Memory, I/O ports, and within
    Instruction
  • Control Transfer direct, indirect addressing
  • the modes available
  • register addressing REG
  • immediate addressing within Instruction
  • direct addressing
  • register indirect addressing
  • based addressing
  • indexed addressing
  • based indexed addressing

MEM or I/O
4
Addressing Modes
  • Register Operand Addressing Mode
  • can be accessed in byte, word, or double word
    sizes.
  • MOV AX, BX
  • Byte AL, AH, BL, BH, CL, CH, DL, DH
  • Word AX, BX, CX, DX, SP, BP, SI, DI, CS, DS,
    SS, ES, FS, GS
  • Double Word EAX, EBX, ECX, EDX, ESP, EBP, ESI,
    EDI
  • See Fig 3.8 in page 64
  • Immediate Operand Addressing
  • an operand is part of the instruction
  • MOV AL, 15H
  • 8 bits, 16 bits, and 32 bits in length
  • See Fig 3.10 in page 67

5
Register Addressing
0000
01000 8B MOV AX, BX 01001
C3 01002 XX
0100
ABCD
XXXX
ABCD
6
Immediate Addressing
0000
01000 B0 MOV AL, 15H 01001
15 01002 XX
0100
XX
15
7
Direct Addressing
  • 16-bit Memory Operand Addressing Modes
  • 16-bit addressing modes and 32-bit addressing
    modes
  • Physical address Segment Base EA(effective
    address)
  • Segment Base Address(SBA) the starting location
    of the segment
  • EA the offset of the operand from the beginning
    of the segment of memory
  • EA Base Index Displacement
  • Base BX or BP, Index SI or DI,
    displacement 8-bit or 16-bit

8
16-bit Memory Operand Addressing
  • Direct Addressing Mode
  • PA Segment Base Direct Address
  • MOV CX, 1234H

MOV CX, 1234H
9
16-bit Memory Operand Addressing
  • Register Indirect Addressing Mode
  • PA Segment Base Indirect Address
    BX,BP,SI,DI
  • example MOV AX, SI

MOV AX,SI
10
16-bit Memory Operand Addressing
  • Based Addressing Mode
  • PA Segment Base BX or BP 8-bit or 16-bit
    displacement
  • Base register the beginning of a data structure
    (See Fig 3.16 (b) in page 74
  • Example MOV BX1234H, AL

MOV BX1234H, AL
11
16-bit Memory Operand Addressing
  • Indexed Addressing Mode
  • PA Segment Base SI, DI8-bit or 16-bit
    displacement
  • Displacement the starting address of an array
    Index selects the specific element in the array
  • Example MOV AL, SI2000H

8A 44 34 12 XX
MOV AL, SI1234H
0000
0100
0200
Element n-1
Index Register
XX
1000
Array of data

BE
05234 05235
Element 1
Displacement
Element 0
2000
12
16-bit Memory Operand Addressing
  • Based-Indexed Addressing Mode
  • PA Seg Base BX, BPSI,DI8-bit or 16-bit
    displacement
  • to access complex data structures
  • See fig 3.20 in page 80
  • Example MOV AH, BXSI1234H
  • opcode 8A 44 34 12

13
32-bit Memory Operand Addressing Modes
  • Enhanced in two ways
  • Scale factor EA base (index x scale factor)
    displacement
  • PA Segment Base EA

14
32-bit Memory Operand Addressing Modes
  • See fig 3.23 in page 83 change 16-bit
    displacement to 32-bit displacement
  • How can we specify the 32-bit extension modes?
  • Default (D) bit in the code segment descriptor
  • 2 prefixes to the instruction set
  • Operand size prefix
  • Address size prefix
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