Addressing Modes in 8086 Microprocessor [Types of 8086 addressing modes]

Addressing Mode refers to the different ways in which a processor can access data. 

The various Addressing Modes present in 8086 Microprocessor are:

1. Immediate Addressing Mode
2. Register Addressing Mode
3. Direct Addressing Mode
4. Register Indirect Addressing Mode
5. Base Plus Index Addressing Mode
6. Register Relative Addressing Mode
7. Base Relative Plus Index Addressing Mode

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A. Immediate Addressing Mode:

• Data immediately follow the hexadecimal opcode in the memory.
• Immediate data are constant data. 
• It transfers the immediate data in Register or Memory location.
• For Example:
•  MOV AL,20 H (copies 20 to AL)
• MOV AX,2050 H (copies 2050 to AX)
• MOV CL, 10000001B (copies Binary value to CL)

• Instruction	Source	Destination
  MOV AL,30 H	Data: 30 H	Register AL

B. Register Addressing Mode:

• It is the most common form of data addressing.
• It transfers a byte/word form source register to destination register.
• It is carried out with 8 bit registers AH,AL,BH,BL,CH,CL,DH & DL or with 16 bit registers AX,BX,CX,DX,SP,BP,SI and DI.
• Never mix an 8 bit register with a 16 bit register i.e. MOV AX, BL.
• 
  

  Instruction	Source	Destination
  MOV AX,BX	REGISTER BX	REGISTER AX

• For example:
• MOV AL, BL  ( Copies BL into AL )
• MOV AX, CX  ( Copies CX into AX )
• MOV ES, DS  ( Copies DS into ES )

C. Direct Addressing Mode:

• The address of the data is defined in the instruction itself.
• When a memory location is to be referenced, its offset address must be specified.

• Instruction	Source	Destination
  MOV AL,[1234H]	ASSUME DS=1000H 10000H + 1234H= 11234H MEMORY LOCATION 11234 H	REGISTER AL

• For Examples:
• MOV AL, [1234H] ( Copies the byte content of data segment memory location                                     11234H into AL.)

D. Register Indirect Addressing Mode:

• The offset address held in Base or Index Register[BP, BX, DI and SI] help to specify the data in a memory location.
• It transfers byte/word between a register and a memory location addressed by an index or base registers. 
• The symbol [ ] denote indirect addressing. 

• Instruction	Source	Destination
  MOV CL,[BX]	ASSUME DS=1000H ASSUME BX=0300H 10000H + 0300H = 10300H MEMORY LOCATION 10300H	REGISTER CL

• For Example:
• MOV CX, [BX]  ( Copies the word contents of the data segment memory               location addressed by BX into CX.)
• MOV [DI], BH  (Copies BH into the data segment memory location addressed by DI.)

E. Base Plus Index Addressing Mode:

• This type of addressing uses one base register (BP or BX) and one Index Register (DI or SI) to indirectly address memory.

• Instruction	Source	Destination
  MOV [BX+SI],CL	REGISTER CL	ASSUME DS=1000H ASSUME BX=0300H ASSUME SI =0200H 10000H + 0300H + 0200H = 10500H MEMORY LOCATION 10500H

• For Example:
• MOV CX, [BX+DI]  (Copies the word contents of the data segment memory    location addressed by BX plus DI into CX. )

F. Register Relative Addressing Mode:

• In this Addressing mode, the data in memory are specified by adding the displacement to the content of Base or an Index register (BP, BX ,DI or SI).
• Transfers a byte/word between a register and the memory location addressed by an index or base register plus a displacement. 

• Instruction	Source	Destination
  MOV [BX+4],CL	REGISTER CL	ASSUME DS=1000H ASSUME BX=0300H 10000H + 0300H + 4H = 10304H MEMORY LOCATION 10304H

• For example: 
• MOV [SI+4], BL : Copies BL into the data segment memory location  addressed by SI plus 4.

G. Base Relative Plus Index Addressing Mode:

• The base relative plus index addressing mode is similar to the base plus index addressing mode but it adds a displacement to form a memory address. 
• Transfers a byte or word between a register and the memory location addressed by a base and an index register plus a displacement. 

• Instruction	Source	Destination
  MOV [BX+SI+05],CL	REGISTER CL	ASSUME DS=1000H ASSUME BX=0300H ASSUME SI =0200H 10000H + 0300H + 0200H +05H = 10505H MEMORY LOCATION 10505H

• For example: 
• MOV DH, [BX+DI+20H] :  Copies the byte contents of the data segment  memory location addressed by the sum of BX, DI and 20H into DH.

Conclusion: 

In assembly language statements, the addressing mode is indicated in the instruction itself. So these are the seven addressing modes in 8086 microprocessor. 

Related Posts: 

• 8085 Microprocessor Features, Pin Diagram, Architecture
• 8086 Microprocessor Features, Architecture
• All 8085 Instructions with Operand, Size, Addressing Mode, Machine Cycle, T-States
• Timing Diagram [8085 Microprocessor]