Lect 3: Instruction Set and Addressing Modes

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: Basic Instruction Set Basic + Extended Instruction Set Basic + Extended specific Instruction Set System control Instruction set System control Instruction set 8086/ Protected Mode Real Mode

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

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 MOVAL, 15H 8 bits, 16 bits, and 32 bits in length See Fig 3.10 in page 67

ABCD Register Addressing 0000 IP CS DS SS ES FS GS AX BX CX DX SP BP SI DI Address Memory Content Instruction MPU 0100 XXXX ABCD B MOV AX, BX C XX

Immediate Addressing 0000 IP CS DS SS ES FS GS AX BX CX DX SP BP SI DI Address Memory Content Instruction MPU B0 MOV AL, 15H XX XX 15

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

16-bit Memory Operand Addressing –Direct Addressing Mode PA = Segment Base : Direct Address MOV CX, [1234H] IP CS DS SS ES FS GS AX BX CX DX SP BP SI DI B 0E XX XXXX ED BE BEED

16-bit Memory Operand Addressing –Register Indirect Addressing Mode PA = Segment Base : Indirect Address {BX,BP,SI,DI} example : MOVAX, [SI] MOV AX,[SI] IP CS DS SS ES FS GS AX BX CX DX SP BP SI DI B 04 XX XXXX ED BE BEED 1234

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 [BX]+1234H, AL MOV [BX]+1234H, AL IP CS DS SS ES FS GS AX BX CX DX SP BP SI DI XX ED 1000 Displacement Base Register + Element 0 Element 1 Data Structure Element n-1

16-bit Memory Operand Addressing –Indexed Addressing Mode PA = Segment Base : {SI, DI}+{8-bit or 16-bit displacement} Displacement : the starting address of an array; Index: selects the specific element in the array Example: MOVAL, [SI]+2000H Index Register Displacement + Element 0 Element 1 Array of data Element n-1 IP CS DS SS ES FS GS AX BX CX DX SP BP SI DI A XX XX 1000 MOV AL, [SI]+1234H BE

16-bit Memory Operand Addressing –Based-Indexed Addressing Mode PA= Seg Base: {BX, BP}+{SI,DI}+{8-bit or 16-bit displacement} to access complex data structures See fig 3.20 in page 80 Example: MOVAH, [BX][SI]+1234H opcode : 8A

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

–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 32-bit Memory Operand Addressing Modes