Addressing mode is a way to specify the operand of an instruction. The operand can be a register, a memory location, or an immediate data. The 8085 microprocessor has 7 addressing modes. They are:

1. Immediate Addressing Mode

In this mode, the operand is a data byte. The data byte is specified in the instruction itself. The data byte is written immediately after the opcode. For example, the instruction MVI A, 32H is an example of immediate addressing mode. Here, the operand is 32H.

2. Register Addressing Mode

In this mode, the operand is in one of the registers of the microprocessor. The register is specified in the instruction itself. For example, the instruction MOV A, B is an example of register addressing mode. Here, the operand is in register B.

3. Direct Addressing Mode

In this mode, the operand is in a memory location. The memory location is specified in the instruction itself. For example, the instruction MOV A, 2050H is an example of direct addressing mode. Here, the operand is in memory location 2050H.

4. Register Indirect Addressing Mode

In this mode, the operand is in a memory location whose address is in one of the registers of the microprocessor. The register is specified in the instruction itself. For example, the instruction MOV A, M is an example of register indirect addressing mode. Here, the operand is in the memory location whose address is in register L and H.

5. Implicit Addressing Mode

In this mode, the operand is implicit in the instruction. The operand is not specified in the instruction itself. For example, the instruction HLT is an example of implicit addressing mode. Here, the operand is implicit in the instruction.

6. Register Relative Addressing Mode

In this mode, the operand is in a memory location whose address is obtained by adding a constant to the contents of a register. The register and the constant are specified in the instruction itself. For example, the instruction MVI A, B is an example of register relative addressing mode. Here, the operand is in the memory location whose address is obtained by adding the contents of register B to a constant.

7. Base Register Addressing Mode

In this mode, the operand is in a memory location whose address is obtained by adding the contents of a base register to a constant. The base register and the constant are specified in the instruction itself. For example, the instruction MOV A, B is an example of base register addressing mode. Here, the operand is in the memory location whose address is obtained by adding the contents of register B to a constant.