What is mean by addressing mode? Explain all the addressing mode available in 8085 microprocessor.

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The different ways in which a source operand is denoted in an instruction is known as addressing modes.

In 8085 microprocessor there are 5 types of addressing modes:

1. Immediate Addressing Mode –

In immediate addressing mode the source operand is always data. If the data is 8-bit, then the instruction will be of 2 bytes, if the data is of 16-bit then the instruction will be of 3 bytes.

Examples:

  • MVI B 45 (move the data 45H immediately to register B)
  • LXI H 3050 (load the H-L pair with the operand 3050H immediately)
  • JMP address (jump to the operand address immediately)

2. Register Addressing Mode –

In register addressing mode, the data to be operated is available inside the register(s) and register(s) is(are) operands. Therefore the operation is performed within various registers of the microprocessor.

Examples:

  • MOV A, B (move the contents of register B to register A)
  • ADD B (add contents of registers A and B and store the result in register A)
  • INR A (increment the contents of register A by one)

3. Direct Addressing Mode –

In direct addressing mode, the data to be operated is available inside a memory location and that memory location is directly specified as an operand. The operand is directly available in the instruction itself.

Examples:

  • LDA 2050 (load the contents of memory location into accumulator A)
  • LHLD address (load contents of 16-bit memory location into H-L register pair)
  • IN 35 (read the data from port whose address is 35)

4. Register Indirect Addressing Mode –

In register indirect addressing mode, the data to be operated is available inside a memory location and that memory location is indirectly specified by a register pair.

Examples:

  • MOV A, M (move the contents of the memory location pointed by the H-L pair to the accumulator)
  • LDAX B (move contents of B-C register to the accumulator)
  • LXIH 9570 (load immediate the H-L pair with the address of the location 9570)

5. Implied/Implicit Addressing Mode –

In implied/implicit addressing mode the operand is hidden and the data to be operated is available in the instruction itself.

Examples:

  • CMA (finds and stores the 1’s complement of the contents of accumulator A in A)
  • RRC (rotate accumulator A right by one bit)
  • RLC (rotate accumulator A left by one bit)
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