Introductions are commands to perform a task in the microprocessor. The instructions consist of opcode and data called an operand. The operand may be the source only, destination only or both of them. Similarly, the destination can be a register, a memory location, or an output port. The various format of specifying the operands are called Addressing mode. The 8085 has five addressing modes.they are given below:
- Direct Addressing Mode
- Register Direct Addressing Mode
- Register Indirect Addressing mode
- Immediate Addressing Mode
- Implied/Implicit Addressing mode
Direct Addressing Mode:
The instructions using this mode specifies an effective address as a part of the introduction. The instruction size either 2-bytes or 3-bytes with first-byte op-code followed by 1 or 2 bytes of address of data.
E.g: LDA 9500H
IN 80H
This type of addressing is called absolute addressing.
Register Direct Addressing Mode
This mode specifies the register or register pair that contains the data.
E.g MOV A, B
Here, register B contains data rather than the address of the data. Other examples are ADD, XCHG, etc.
Register Indirect Addressing mode
In this mode, the address part of the instruction specifies the memory whose contents are the address of the operand. So in this type of addressing mode, it is the address of the address rather than address itself. (One operand is register)
E.g MOV R, M MOV M, R STAX,LDAX etc.
Immediate Addressing Mode
In this mode, the operand position is the immediate data. For 8-bit data, instruction size is 2 bytes and for 16-bit data, instruction size is 3 bytes.
E.g. MVI A, 32H
LXI B,4567H
Implied/Implicit Addressing mode
The instructions of this mode do not have operands.
E.g. NOP: No operation
HLT: Halt
EI: Enable interrupt
DI: Disable interrupt
