8085 Addressing Modes Basic Tutorial-Computerstutorial

8085 Addressing Modes

Addressing modes are the manner of specifying effective address. The instructions MOV B, A or MVI A, 82H are to copy data from a source into a destination. In these instructions the source can be a register, an input port, or an 8-bit number (00H to FFH). Similarly, a destination can be a register or an output port. The sources and destination are operands. The various formats for specifying operands are called the ADDRESSING MODES.8085 Addressing mode are can be classified into:

Immediate addressing.

Register addressing.

Direct addressing.

Register Indirect addressing.

Immediate addressing 

In immediate addressing mode, the data is specified in the instruction itself. The data will be a part of the program instruction. Data is present in the instruction. Load the immediate data to the destination provided.

Example: MVI A  06 // in this example move 06 in register A.

Direct addressing:

In direct addressing mode, the address of the operand  (data) is specified in the instruction. The data will be in memory. In this addressing mode, the program instructions and data can be stored in different memory. Used to accept data from outside devices to store in the accumulator or send the data.

Example:

STA 2000H // Store the contain of the accumulator in the memory location 2000H .

Difference between the direct addressing modes and immediate addressing modes

Direct addressing

Register Addressing:

in register addressing mode the operand(data) are in the  general purpose register. the opcode specifies the address of the register in addition to the operation to be performed.

Example:

MOV A, B // Move the content of register B to register A .

ADD B // Add the contain of register B to the contain of Register A.

Register Indirect addressing:

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

Example:

MOV M , A// Here the HL register pair is used as a pointer to memory location. The content of Accumulator is copied to that location

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