The 8085 Addressing Modes

The 8085 Addressing Modes

The instructions MOV B, A or MVI A, 82H are to copy data from a source into a destination. In these instructions the source can be a register, an input port, or an 8-bit number (00H to FFH). Similarly, a destination can be a register or an output port. The sources and destination are operands. The various formats for specifying operands are called the ADDRESSING MODES. For 8085, they are:

ü Immediate addressing.

ü Register addressing.

ü Direct addressing.

ü Indirect addressing.

Immediate addressing:

Data is present in the instruction. Load the immediate data to the destination provided.

Example: MVI R,data

Register addressing:

Data is provided through the registers.

Example: MOV Rd, Rs

Direct addressing:

Used to accept data from outside devices to store in the accumulator or send the data stored in the accumulator to the outside device. Accept the data from the port 00H and store them into the accumulator or Send the data from the accumulator to the port 01H.

Example: IN 00H or OUT 01H

Indirect Addressing:

This means that the Effective Address is calculated by the processor. And the contents of the address (and the one following) is used to form a second address. The second address is where the data is stored. Note that this requires several memory accesses; two accesses to retrieve the 16-bit address and a further access (or accesses) to retrieve the data which is to be loaded into the register.