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Addressing Modes

Addressing Modes. • Instruction – Op-code – Operand • Addressing mode indicates a way of locating data or operands. – Any instruction may belong to one or more addressing modes – Some instructions may not belong to any of the addressing modes. Addressing Modes.

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Addressing Modes

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  1. Addressing Modes • Instruction – Op-code – Operand • Addressing mode indicates a way of locating data or operands. – Any instruction may belong to one or more addressingmodes – Some instructions may not belong to any of the addressing modes

  2. Addressing Modes • Data-Addressing Modes • Program Memory-Addressing Modes • Stack Memory-Addressing Modes

  3. Addressing Modes • Immediate: The data is either 8 bits or 16 bits long and is part of the instruction Example – MOV AX,0001H – MOV CX,0045H – MOV BL,08H – MOV AH,BFH

  4. Direct: The 16-bit effective address of the data is part of the instruction • Example: – MOV AX, [5000H] – ADD AX, [1000H]

  5. Register addressing: The datum is in the register that is specified by the instruction. For a 16-bit operand, a register may be AX, BX, CX, DX,SI,DI,SP or BP. For an 8 bit operand a register may be AL, AH, BL, BH, CL, CH, DL, DH. • Example : MOV AX,BX ADD AL, BL

  6. Register Indirect: The effective address of the data is in the base register BX or an index register that is specified by the instruction Example: MOV AX, [BX] MOV AX,[SI]

  7. Register Relative: The effective address is the sum of an 8 or 16 bit displacement and the contents of a base register or an index register

  8. Example • If (BX)=0158 (DI)=10A5 Displacement=1B57 (DS)=2100 and DS is used as the segment register, then the effective and physical address produced by these quantities and the various addressing modes would be Direct: EA=_______ PA=______ Register indirect assuming register BX:EA=___ PA=_____ Register relative assuming register BX:EA=__ PA=______ Based indexed assuming BX and DI:EA=____ PA=______ Relative based indexed assuming BX and DI:EA=______ PA=______

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