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ADDRESSING MODES

HETA J DESAI

SDJINTERNATIONAL COLLEGE

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Addressing Modes

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To perform any operation, we have togive the corresponding instructions to

the microprocessor.

In each instruction, programmer has to

specify 3 things:

Operation to be performed.

Address of source of data.

Address of destination of result.

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OP CODE The first part of instructionwhich specifies task to be performed is

called op-code

Operand The second part of instruction isthe data to be operated on is called

operands.

First byte is op code rest are operands.

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Addressing Modes of 8085

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The method by which the address ofsource of data or the address of

destination of result is given in the

instruction is called AddressingModes.

Addressing modes are various

technique to specify data for instructions.

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Types of Addressing Modes

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1. Direct Addressing Mode

2. Register Addressing Mode

3. Register Indirect Addressing Mode

4. Immediate Addressing Mode

5. Implicit Addressing Mode

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Direct Addressing Mode

In this mode, the address of theoperand is given in the instructionitself.[Memory address is directly

given]

STA is the operation.

2500 H is memory address where data is to be stored It is to be understood that source of data is accumulator

Accumulator is a register for short-term, intermediate storage

of arithmetic and logic data in a computer's CPU (central

processing unit).

STA 2500 H

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Store content of accumulator

in the memory location 2400H.

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http://whatis.techtarget.com/definition/registerhttp://searchcio-midmarket.techtarget.com/definition/CPUhttp://searchcio-midmarket.techtarget.com/definition/CPUhttp://whatis.techtarget.com/definition/register

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Register Addressing Mode

In this mode, the operand is in generalpurpose register.

MOV is the operation.

B is the source of data.A is the destination.

MOV A, B

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Move the contents of register B toA.

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Register Indirect Addressing

Mode In this mode, the address of operand is specified by a register pair.

L11 H,2500 H LOAD H-L PAIR WITH 2500 H.

now next instruction after this is register indirect addressing technique.

MOV is the operation.

M is the memory location specified byH-Lregister pair.

Ais the destination.

The address of memory is not directly given in to instruction. The

address resides in H-L pair. And this has already been given in

earlier instruction.

MOV A, M

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Move data from memory location

whose address in H-L pair to

accumulator accumulator.

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Immediate Addressing Mode

In this mode, the operand is specifiedwithin the instruction itself.

MVI is the operation.

05 is the immediate data (source).A is the destination.

MVI A, 05

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Move 05 in register A.

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Implicit Addressing Mode

If address of source of data as well asaddress of destination of result is fixed,then there is no need to give anyoperand along with the instruction.

RAL Rotate the content of the accumulator

left by one bit.

RAL is the operation.

A is the source.

A is the destination.

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