P9 8086 Addressing Modes

8/5/2013

1

Dr. M. Tariq Dr. M. Tariq Dr. M. Tariq Dr. M. Tariq BandayBandayBandayBandayPG Department of Electronics & Instrumentation

Technology, UoK, Srinagar

P9

Dr. M. Tariq Bandayhttp://banday.info

w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

An Assembly language instruction can be divided into two parts: Operation code (opcode) one- to five-letter mnemonic mnemonic mnemonic mnemonic , and

Operands (None, One or More Operands)

MENMONIC OPRANDSE.g.

MOV AX, BX

MnemonicMnemonicMnemonicMnemonic

SourceSourceSourceSourceSourceSourceSourceSourceOperandOperandOperandOperand

DestinationDestinationDestinationDestinationDestinationDestinationDestinationDestinationOperandOperandOperandOperand


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

The move (MOV) instruction is used totransfer a byte or a word of data from asource operand to a destination operand.

Examples: MOV AX, BX

MOV AX, [BX]

MOV BX, [2000]


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Note that the MOV instruction cannot transfer data directly between external memory.

MTBStamp

8/5/2013

2


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

An Addressing mode is defined as amethod of specifying the effectiveaddress of the operands in memory.

The addressing mode increases theflexibility of the programminglanguages.

It is used in implementing the constructsand data structures of the powerful highlevel programming language.


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Implicit Addressing

Immediate Addressing

Register Addressing

Memory Addressing Modes Direct Addressing

Indirect Addressing

Register Indirect Addressing

Based Addressing

Indexed Addressing

Based Indexed Addressing

Inter Segment Direct Addressing

Inter Segment Indirect Addressing


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

In this mode the instruction assumes that data is in some pre defined register which varies from one instruction to other. Such instructions are also called zero address instructions. E.g. CMC

STD

CLC, etc.

OPCODEOPCODEOPCODEOPCODE

Instruction


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

In this mode data (Operand) is part of theinstruction. It does not involve computationof address.

e.g.

MOV AX, 100h AX100h

MOV AL, 15h AL15h

OPCODEOPCODEOPCODEOPCODE DATADATADATADATA

Instruction

MTBStamp

8/5/2013

3


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Status of CPU before Execution of InstructionMOV AL, 15H


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

After Execution of Instruction MOV AL, 15H


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

In this mode, operands on which instructionsoperate are stored in some internal registerof the microprocessor. Operand may be insome 16 bit or 8 bit register.

16 bit register may be any one from: AX, BX, CX,DX, SP, BP, SI, DI, CS, DS, SS or ES

8 bit register may be AL, AH, BL, BH, CL, CH, DL orDH


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

OPCODEOPCODEOPCODEOPCODE RegisterRegisterRegisterRegister

Instruction

DataDataDataData

Register

E.g.

MOV AX, BX AXBXMOV AL, CL ALCL

MTBStamp

8/5/2013

4


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Before execution of instruction MOV AX, BX


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

After execution of instruction MOV AX, BX


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Direct Addressing Modes

Indirect Addressing Modes

Register Indirect Addressing

Based Addressing

Indexed Addressing

Based Indexed Addressing

Inter Segment Direct

Inter Segment Indirect


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

To reference an Operand in memory,8086/8088 calculates Physical Address (PA)of the Operand and then initiates a read orwrite operation to this location.

Physical Address (PA) 20 bit address of memory location

Segment Base Address (SBA) 16 bit address of the segment in use as specified byany one of Segment Registers.

Effective Address (EA) 16 bit logical address specifying offset fromsegment base address

8/5/2013

5


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Registers used in computation of Physical address of memory

One of the Segment Registers (CS, SS, DS or ES) and one or more of the following:

One of the Base Registers (BX or BP) BP can not used independently in the addressing mode

One of the Index Registers (SI or DI), and

8 Bit or 16 Bit displacement


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Segment, Base, index and displacement is combined as following:


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

In this mode data is in memory and theaddress of the data is part of the Instruction.The address is hard coded with theinstruction itself.

E.g. MOV AX, [1234H]

OPCODEOPCODEOPCODEOPCODE EAEAEAEA

Instruction

DataDataDataData

Memory

8/5/2013

6


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Before execution of instruction MOV CX, [1234H]


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

After execution of instruction MOV CX, [1234H]


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Assuming DS = 0200H, calculate the PA of memory locations used as source/destination in the following instructions:

MOV CX, [1234H]

MOV [2000H], CL

MOV AL, [1340H]


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

In this addressing mode the effective addressof the Operand is in register. The data onwhich the instruction operates is pointed toby register (BX, SI, DI) which is part of theinstruction.


Instruction

EAEAEAEA

Register

DATADATADATADATA

Memory

e.g.MOV AX, [BX]

MTBStamp

8/5/2013

7


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Computation of Physical Address

PA=Segment Base : Register


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Before execution of Instruction MOV AX, [SI]PA = 0200H X 10H + 1234H = 03234H


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

After execution of Instruction MOV AX, [SI]PA = 0200H X 10H + 1234H = 03234H


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

In this the EA of the Operand is calculated byadding contents of one of Base Registers (BP orBX) and 8 or 16 bit offset. This is a RegisterRelative addressing mode that uses one of theBase Registers.

E.g. MOV [BX]+1234H, AL

MOV [BX + 20h], AL

MOV AX, [BP +2000H]

MTBStamp

8/5/2013

8


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Assuming DS = 0200H, SS = 0400h, BX = 1000H and BP = 2000H Calculate the PA of memory locations used as source/destination in the following instructions:

MOV [BX]+1234H, AL

MOV [BX + 20h], AL

MOV AX, [BP +2000H]

MOV CX,[BX+1000H]


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Address Calculation


Instruction

AddressAddressAddressAddress

Base Register

EAEAEAEA

Memory

DisplacementDisplacementDisplacementDisplacement

++++

DATADATADATADATA


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Address Calculation


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Before execution of instruction MOV [BX] +1234H, AL

PA = 0200H X 10H + 1000H +1234H = 04234H

MTBStamp

8/5/2013

9


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

After execution of instruction MOV [BX] +1234H, AL

PA = 0200H x 10H + 1000H +1234H = 04234H


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

In this the EA of the Operand is calculated byadding contents of one of Index Registers (SI orDI) and 8 or 16 bit offset. This is a RegisterRelative addressing mode that uses one of theIndex Registers.

E.g. MOV [SI]+1234H, AL

MOV [DI+ 20h], AL

MOV AX, [SI+2000H]


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Address Calculation


Instruction


Index Register

EAEAEAEA

Memory


++++

DATADATADATADATA


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Address Calculation

MTBStamp

8/5/2013

10


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Before execution of instruction MOV AL, [SI] +1234H

PA = 0200H X 10H + 2000H +1234H = 05234H


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

After execution of instruction MOV AL, [SI] +1234H

PA = 0200H X 10H + 2000H +1234H = 05234H


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

In this the EA of the Operand is calculated byadding contents of one of Base registers (BX orBP), one of Index Registers (SI or DI) and 8 or 16bit offset. This is a Register Relative addressingmode that uses one of the Index Registers.

E.g. MOV [BX + SI]+1234H, AL

MOV [DI+ 20h] [SI + 50H], AL

MOV AX, [BX+SI+2000H]


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Assuming DS = 0200H, ES = 0400h, SI= 1000H and DI= 2000H Calculate the PA of memory locations used as source/destination in the following instructions:

MOV [SI]+1234H, AL

MOV [SI+ 20h], AL

MOV AX, [DI+2000H]

MOV CX, [DI+1000H]

MTBStamp

8/5/2013

11


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Address Calculation


Instruction


Index Register

EAEAEAEA

Memory


++++

DATADATADATADATA

RegisterRegisterRegisterRegister


Base Register


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Address Calculation


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Before execution of instruction MOV AH, [BX][SI] + 1234H

PA = 0200H X 10H + 1000H +2000H +1234H = 05234H


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

After execution of instruction MOV AH, [BX][SI] + 1234H

PA = 0200H X 10H + 1000H +2000H +1234H = 05234H

MTBStamp

8/5/2013

12


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Assuming DS = 0200H, ES = 0400h, SI= 1000H, BX=2000H, BP =1230H and DI= 2000H Calculate the PA of memory locations used as source/destination in the following instructions:

MOV [BX]+[SI] +1234H, AL

MOV [BX][SI], AL

MOV AX, [BP+ DI + 2000H]

MOV CX, [BX][SI]+1234H


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Inter Segment Direct CALL 0050H

Inter Segment Indirect MOV BX, 0050H

CALL BX

Intra Segment Direct CALL 2000H:0050H

Intra Segment Indirect MOV BX, 2000H

MOV DI, 0050H

CALL BX:DI


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

MTBStamp

8/5/2013

13


w

w

w

.

b

a

n

d

a

y

.

i

n

f

o

www.banday.info

www.banday.info

Thank you

Any Questions?

MTBStamp

Documents

P9 8086 Addressing Modes