Addressing modes in 8085 microprocessor

Prerequiste – Addressing modes
The way of specifying data to be operated by an instruction is called addressing mode.

Types of 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 01)

  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 b 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 contains 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 contains of accumultor A in A)
    RRC (rotate accumulator A right by one bit)
    RLC (rotate accumulator A left by one bit)



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