ADDRESSING MODES OF 8051

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-SHARIQUE MULLA

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WHAT IS AN ADDRESSING MODE?

• An Addressing mode is a way to address an operand.

• Operand means the data we are operating upon (in most cases source data).

• It can be a direct address of memory, it can be any numerical data, etc.

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ADDRESSING MODES

1. Immediate addressing mode

2. Direct addressing mode

3. Register direct addressing mode

4. Register indirect addressing mode

5. Indexed addressing mode

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1) IMMEDIATE ADDRESSING MODE

• This type of addressing mode is named as “immediate addressing”, because it transfers an 8-bit data immediately to the accumulator (destination register).

• This instruction has an 8-bit immediate data at the operand.

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• Example- MOV A,#6AH

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2) DIRECT ADDRESSING MODE

• This is an another way of addressing an operand.

• In this type of addressing mode, the address of the data (source data) is given as operand instead of immediate data .

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• Example- MOV A,04H

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3) REGISTER DIRECT ADDRESSING MODE

• In this type of addressing mode, we use the register name directly as source operand.

• In 8051,there are 4 register banks, containing 8 registers (R0-R7) each.

• Hence, the selection of a register bank is done by a special function register (SFR) called Processor Status Word (PSW).

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• Example- MOV A,R4

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4) REGISTER INDIRECT ADDRESSING MODE

• In this type of addressing mode, the address of the data (source data) is given in the register operand.

• Here also, the register bank is required to be selected by PSW (Processor Status Word).

• Here, the selected register is first loaded with a value which acts as the address of the data.

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• Example- MOV A,@R0

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5) INDEXED ADDRESSING MODE

• In this type of addressing, DPTR (Data Pointer) or PC (Program Counter), i.e. 16-bit registers, are used in the instruction.

• Here, the content of DPTR or PC is added to the current content of accumulator.

• The result acts as the address of the source data.

• After execution the source data is stored in accumulator.

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• Example- MOV A,@A+DPTR

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PROCESSOR STATUS WORD (PSW)

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THANK YOU

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