Addressing Modes

A microprocessor only understands binary code, not assembly language instructions. Assembly instructions are converted into binary code, known as machine code. Instructions can be 1, 2, or 3 bytes long. The first byte specifies the operation, while the second and third bytes indicate the operand or its address.        

Direct Addressing 

The direct addressing mode, the address of the operand is specified within the instruction itself. For example, LDA 06C2_H. This means Load accumulator with the contents of memory location 06C2_H. Here all instructions are three-byte instructions. 

Register Addressing Mode 

In this mode the register name is specified in the instruction. Address is not required for this type. These are single byte instructions. 

Register Indirect Addressing 

In register indirect addressing, the contents of register pair point to the address of the operand. Some of the instructions of 8085 use combined addressing modes from the ones mentioned above. 

Immediate Addressing 

When data (operand) is directly transferred to register then it is known as immediate Addressing. One or two byte instructions are used for this type  of addressing. In this mode, operand is specified within the instruction itself. Data is specified after immediate Mnemonic 

Implied Addressing

The addressing mode of certain 8085 instructions is implied by  the instruction's functions. For example, the STC (set carry flag) instruction deals with the carry flag only. Here there is no need to specify the address as it is inherent.