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C. S. Manjula, Grad IETE
Lab Mechanic
Computer Engineering
S.P.W. Polytechnic, Tirupati,
IV semester
Microprocessors
CM 405
Instruction Set
100 Minutes
Addressing Modes of 8086
PPT
K.Srikanth,Lecturer,GPT, Nizamabad
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Addressing Modes of 8086
Definition
Addressing mode indicates the method through which an
operand is specified or indicated in an instruction
Types of Addressing Modes: 11
1. Immediate Addressing mode
2. Direct Addressing mode
3. Register Addressing mode
4. Register Indirect Addressing mode
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Addressing Modes of 8086 (Contd..)
5. Register Relative Addressing mode
6. Based Indexed Addressing mode
7. Relative Based Indexed Addressing mode
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Branch Related Addressing Modes
8. Intra-segment Direct Addressing mode
9. Intra-segment Indirect Addressing mode
10. Inter-segment Direct Addressing mode
11. Inter-segment Indirect Addressing mode
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1. Immediate Addressing mode
Operand is indicated in the instruction itself
Ex:
MOV AX, 0007H
0007H is the immediate data here.
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2. Direct Addressing mode
• Offset Address of the operand is specified directly in the
instruction
EX: MOV AX , [5000H]
NOTE:1.[ ] indicates offset or effective address
2. Data resides in the Data Segment (DS),
whose Physical address is computed as
PA = DS x 10H + 5000H
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3. Register Addressing mode
The register which holds the data is mentioned in the
instruction
Ex: MOV BX, AX
All the registers, except IP and CS may be used
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4. Register Indirect Addressing
•
•
Offset address is stored in a register
That register is indicated in the instruction
EX: MOV AX, [BX]
•
•
•
The offset address of the data is in BX.
The Physical Address (PA) is given as:
PA = [DS] x 10H + [BX]
• Permitted Registers: SI, DI, BX
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5. Register Relative Addressing mode
• Offset address is stored in a register
• Permitted Registers: SI, DI, BX, BP
• That register, and an 8-bit or 16-bit displacement are
given within the instruction
• The Offset Address of the data is computed by adding
the displacement with the memory offset address
present in the given register
EX: MOV AX, 50H[BX]
Offset address = 50H + [BX]
PA = 10H * DS + 8 or 16 bit relative addr.
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6. Based Indexed Addressing
• A base register (BX/BP), and an index register (SI/DI)
are given within the instruction
• The Effective Address of the data is computed by adding
the addresses present in the base and index regs.
EX: MOV AX, [BX] [SI]
EA = [BX] + [SI]
PA = 10H * DS + EA
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7. Relative Based Indexed Addressing Mode
• A base register (BX/BP), an index register (SI/DI), and
an 8-bit or 16-bit displacement are given within the
instruction
• The Effective Address of the data is computed by adding
the addresses present in the given registers with the 8bit or 16-bit displacement
EX: MOV AX, 50H [BX][SI]
EA = [BX] + [SI] + 50H
PA = 10H * DS + EA
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Branch Related Addressing Modes
Instructions under this category doesn’t try to access
data, instead they alter normal sequence of program
execution (By branching to an instruction somewhere
else)
• Inter segment branch – Branching within the same code
segment
• Intra segment branch – Branching into another code
segment
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8. Intra-segment Direct Addressing mode
• An 8-bit or 16-bit displacement is given within the
instruction
• The effective branch address (code segment offset
address) is given as the sum of 8-bit or 16-bit
displacement and the contents of Instruction Pointer (IP)
and lies within the same segment
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9. Intra-segment Indirect Addressing mode
• The address of a register or a memory location, where
the 16-bit code segment offset address is located, is
given within the instruction
• A branch is affected by copying this offset address into
IP register
• This branch is to a location within the code segment
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10. Inter-segment Direct Addressing Mode
• Two 16-bit values, specifying the base and offset
addresses of the code segment, are given within the
instruction
• A branch is affected by copying the contents of the
above mentioned addresses into CS and IP registers.
This branch can be to a location outside the code
segment
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11. Inter-segment Indirect Addressing Mode
• The starting address of a memory block, containing the
base and offset addresses of the code segment, is
specified using any of the data related addressing
modes
• A branch is affected by copying the contents of the
above mentioned memory block into CS and IP
registers. This branch can be to a location outside the
code segment
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Summary
We have discussed about
•
Types of addressing modes
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Quiz
1.What do you mean by addressing mode ?
a)
Locating ALU
b)
Locating operand
c)
Locating memory
d)
Locating register
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Quiz (Contd.)
2.The length of an instruction of 8086 can be ?
a)
1 to 4 bytes
b)
2 to 4 bytes
c)
1 to 6 bytes
d)
2 to 6 bytes
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Quiz (Contd.)
3.What is meant by inter segment addressing
mode ?
a) Branch address is available in the same segment
b) Branch address is available outside the segment
---------------------------------------------------------
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Frequently Asked Questions
1.
List out addressing modes supported by 8086 ?
2.
Explain each addressing mode by using suitable
examples ?
3.
Compare direct and indirect addressing modes and
explain the similarities and differences with suitable
examples
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